Merge commit 'd1f24cf6' into remed/lane-K

2026-10-22 17:13:56 -04:00
parent abbaac3615 d1f24cf6a7
commit 31605e547d
105 changed files with 9559 additions and 831 deletions
@@ -57,6 +57,14 @@ public sealed class ReadCommand : ModbusCommandBase
        ValidateEndpoint();
        var ct = console.RegisterCancellationHandler();

+        // The driver's tag factory refuses an incompatible region/type pair (the tag would read
+        // BadNodeIdUnknown) — say why up front instead.
+        if (!ModbusTagDefinitionFactory.IsRegionTypeCompatible(Region, DataType))
+            throw new CliFx.Exceptions.CommandException(
+                Region is ModbusRegion.Coils or ModbusRegion.DiscreteInputs
+                    ? $"Region '{Region}' only carries Bool values (--type Bool); got '{DataType}'."
+                    : $"Region '{Region}' carries register types; use --type BitInRegister for a bit of a register, not '{DataType}'.");
+
        var tagName = SynthesiseTagName(Region, Address, DataType);
        var tag = new ModbusTagDefinition(
            Name: tagName,
@@ -74,6 +74,9 @@ public sealed class WriteCommand : ModbusCommandBase
            throw new CliFx.Exceptions.CommandException(
                $"Region 'Coils' only supports boolean values (--type Bool). " +
                $"Type '{DataType}' cannot represent a single-bit coil write.");
+        if (!ModbusTagDefinitionFactory.IsRegionTypeCompatible(Region, DataType))
+            throw new CliFx.Exceptions.CommandException(
+                $"Region '{Region}' carries register types; use --type BitInRegister for a bit of a register, not '{DataType}'.");

        var tagName = ReadCommand.SynthesiseTagName(Region, Address, DataType);
        var tag = new ModbusTagDefinition(
@@ -89,13 +89,24 @@ public sealed class ModbusDriverOptions
    public bool UseFC16ForSingleRegisterWrites { get; init; } = false;

    /// <summary>
-    ///     <b>Reserved / no-op</b> kill-switch for FC23 (Read/Write Multiple Registers). The
-    ///     driver does not currently emit FC23 — toggling this option has no observable effect
-    ///     today. The slot exists so a future block-read-coalescing enhancement that opts into
-    ///     FC23 can be disabled per-deployment without a code change. Default <c>false</c>.
+    ///     Hard kill-switch for FC23 (Read/Write Multiple Registers): when <c>true</c> the driver never
+    ///     emits FC23, even with <see cref="UseFC23ForMultiRegisterWrites"/> set. Default <c>false</c>.
+    ///     FC23 is OPT-IN — a config without <see cref="UseFC23ForMultiRegisterWrites"/> keeps the FC16 wire
+    ///     behaviour, so the persisted <c>"disableFC23": false</c> every form-saved config carries changes
+    ///     nothing on the wire.
    /// </summary>
    public bool DisableFC23 { get; init; } = false;

+    /// <summary>
+    ///     Opt-in: send a multi-register holding write (2–121 registers: 32/64-bit values, arrays, strings)
+    ///     as ONE FC23 that writes the block and reads the same block back, so the device confirms what it
+    ///     now holds. A unit that answers FC23 with exception 01 (MELSEC QJ71MT91, S7 Modbus servers) moves
+    ///     to FC16 for that write and every later one until the next initialize; one that fails FC23 at the
+    ///     transport moves too (that one write is reported as a comms failure). Ignored when
+    ///     <see cref="DisableFC23"/> is set. Default <c>false</c> = FC16, the historical behaviour.
+    /// </summary>
+    public bool UseFC23ForMultiRegisterWrites { get; init; } = false;
+
    /// <summary>
    ///     Interval for the background re-probe loop that retries auto-prohibited
    ///     coalesced ranges. When non-null, every <c>AutoProhibitReprobeInterval</c>
@@ -107,20 +118,32 @@ public sealed class ModbusDriverOptions
    public TimeSpan? AutoProhibitReprobeInterval { get; init; } = null;

    /// <summary>
-    ///     Block-read coalescing budget. When non-zero, the read planner combines tags
-    ///     in the same (UnitId, Region) group whose addresses are at most this many registers
-    ///     apart into a single FC03/FC04/FC01/FC02 read. The sliced response is then dispatched
-    ///     back to per-tag values. Default <c>0</c> = no coalescing — every tag gets its own
-    ///     PDU (preserves the previous behaviour). Typical opt-in values are 5..32 — large enough
-    ///     to bridge a few unused registers, small enough to avoid trampling protected holes.
+    ///     Block-read coalescing budget. When non-zero, the read planner combines tags in the same
+    ///     (UnitId, Region) group whose addresses are at most this many registers (Coils / DiscreteInputs:
+    ///     bits) apart into a single FC03/FC04/FC01/FC02 read, then slices the response back into per-tag
+    ///     values (several <c>BitInRegister</c> tags on one status word fold into one read). <c>0</c> = no
+    ///     coalescing — an explicitly authored 0 keeps that historical meaning. Default <c>8</c> applies
+    ///     only when the key is ABSENT. A range the device refuses is auto-prohibited and read per tag.
+    ///     <see cref="DisableReadCoalescing"/> also turns it off; <c>coalesceProhibited</c> exempts one tag.
    /// </summary>
-    public ushort MaxReadGap { get; init; } = 0;
+    public ushort MaxReadGap { get; init; } = DefaultMaxReadGap;
+
+    /// <summary>The default <see cref="MaxReadGap"/> (shared by the factory DTO and the AdminUI form).</summary>
+    public const ushort DefaultMaxReadGap = 8;

    /// <summary>
-    ///     PLC family hint that drives the parser's family-native branch. When set to a
-    ///     non-Generic value, address strings using that family's native syntax (DL205 V2000 /
-    ///     MELSEC D100) parse to the right region + offset directly. Defaults to
-    ///     <see cref="ModbusFamily.Generic"/> = Modicon-only behaviour preserved by default.
+    ///     When <c>true</c>, every tag is read with its own PDU (no block coalescing at all) — for a device
+    ///     that mis-answers merged reads in a way the auto-prohibition cannot catch. Default <c>false</c>.
+    /// </summary>
+    public bool DisableReadCoalescing { get; init; } = false;
+
+    /// <summary>
+    ///     PLC family hint that drives the parser's family-native branch. A STRING-ONLY tag (an
+    ///     <c>addressString</c> with no region/address keys — see <see cref="ModbusTagAddressResolution"/>) is
+    ///     resolved with this family at every initialize, so with a non-Generic
+    ///     value that family's native syntax (DL205 V2000 octal / MELSEC D100) parses to the right
+    ///     region + offset. Defaults to <see cref="ModbusFamily.Generic"/> (Modicon / mnemonic grammar).
+    ///     Tags authored by region + numeric address are unaffected.
    /// </summary>
    public ModbusFamily Family { get; init; } = ModbusFamily.Generic;

@@ -0,0 +1,251 @@
+using System.Text.Json;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus;
+
+/// <summary>
+///     Which part of a Modbus <c>TagConfig</c> blob names the tag's address — the output of
+///     <see cref="ModbusTagAddressResolution.Classify(JsonElement)"/>.
+/// </summary>
+public enum ModbusAddressShape
+{
+    /// <summary>
+    ///     Both <c>region</c> and <c>address</c> are present: those keys are the address, whatever
+    ///     <c>addressString</c> / <c>addressResolved</c> sit beside them (classic, editor-pinned, or a pre-#741 row
+    ///     whose string the old driver never read).
+    /// </summary>
+    Keys,
+
+    /// <summary>
+    ///     The keys are not both present and <c>addressString</c> is a non-blank string: the string is the address,
+    ///     resolved with the DRIVER's family. A family that cannot parse it refuses the tag.
+    /// </summary>
+    StringOnly,
+
+    /// <summary>The keys are not both present and <c>addressString</c> is present but not a string: refused.</summary>
+    InvalidAddressString,
+
+    /// <summary>Neither the keys nor a usable <c>addressString</c>: refused (the tag names no address).</summary>
+    NoAddress,
+}
+
+/// <summary>The address part of a Modbus tag, as the driver will poll it.</summary>
+/// <param name="Shape">Which part of the blob named it (<see cref="ModbusAddressShape.Keys"/> or <see cref="ModbusAddressShape.StringOnly"/>).</param>
+/// <param name="Region">The register region.</param>
+/// <param name="Address">The zero-based offset.</param>
+/// <param name="DataType">The data type (already coerced to <c>Bool</c> for a bit region).</param>
+/// <param name="ByteOrder">The word/byte order.</param>
+/// <param name="BitIndex">The bit index (BitInRegister).</param>
+/// <param name="StringLength">The string length (String).</param>
+/// <param name="ArrayCount">The element count, or <c>null</c> for a scalar.</param>
+public sealed record ModbusResolvedAddress(
+    ModbusAddressShape Shape,
+    ModbusRegion Region,
+    ushort Address,
+    ModbusDataType DataType,
+    ModbusByteOrder ByteOrder,
+    byte BitIndex,
+    ushort StringLength,
+    int? ArrayCount);
+
+/// <summary>The outcome of <see cref="ModbusTagAddressResolution.Resolve(JsonElement, ModbusFamily, MelsecFamily)"/>.</summary>
+/// <param name="Shape">The blob's address shape (always set, also on a refusal).</param>
+/// <param name="Address">The resolved address, or <c>null</c> when the tag is refused.</param>
+/// <param name="Refusal">Why the tag is refused, or <c>null</c> when it resolved.</param>
+public readonly record struct ModbusAddressResolution(ModbusAddressShape Shape, ModbusResolvedAddress? Address, string? Refusal)
+{
+    /// <summary>Whether the driver serves the tag at <see cref="Address"/>.</summary>
+    public bool IsResolved => Address is not null;
+}
+
+/// <summary>
+///     <b>The one authority for which address a Modbus <c>TagConfig</c> names</b> (#741, review r3 N3). The driver's
+///     tag reader, the deploy gate, the AdminUI editor model (load / save / Validate / display) and the CSV
+///     import/export all ask this class; none of them restates the precedence.
+///     <para>The rule:</para>
+///     <list type="number">
+///         <item>When <c>region</c> AND <c>address</c> are both present they are the address
+///         (<see cref="ModbusAddressShape.Keys"/>). No pre-#741 shape changes the address it resolves to: the old
+///         driver read the keys only and ignored any <c>addressString</c>.</item>
+///         <item>Otherwise a non-blank string <c>addressString</c> is the address
+///         (<see cref="ModbusAddressShape.StringOnly"/>), parsed by <see cref="ModbusAddressParser"/> with the
+///         DRIVER's family. If that family cannot parse it the tag is REFUSED — never served as HR[0].</item>
+///         <item>Anything else is refused.</item>
+///     </list>
+///     <c>addressResolved</c> is editor display / CSV state only and never changes the shape.
+/// </summary>
+public static class ModbusTagAddressResolution
+{
+    /// <summary>The TagConfig key carrying the parser-grammar address (<c>40001:F:CDAB</c>, <c>V2000</c>, <c>D100</c>).</summary>
+    public const string AddressStringKey = "addressString";
+
+    /// <summary>
+    ///     The key the editor writes beside the keys it resolved from an <c>addressString</c>
+    ///     (<c>"addressResolved": true</c>). Display / CSV state only: it never decides the address.
+    /// </summary>
+    public const string AddressResolvedKey = "addressResolved";
+
+    /// <summary>Every (family, MELSEC sub-family) a driver can be configured with — the family-unaware gates' search space.</summary>
+    public static IReadOnlyList<(ModbusFamily Family, MelsecFamily Sub)> AllFamilies { get; } =
+    [
+        (ModbusFamily.Generic, MelsecFamily.Q_L_iQR),
+        (ModbusFamily.DL205, MelsecFamily.Q_L_iQR),
+        (ModbusFamily.MELSEC, MelsecFamily.Q_L_iQR),
+        (ModbusFamily.MELSEC, MelsecFamily.F_iQF),
+    ];
+
+    /// <summary>Classifies an object-rooted TagConfig by which part of it names the address.</summary>
+    /// <param name="root">The TagConfig root (a non-object is <see cref="ModbusAddressShape.NoAddress"/>).</param>
+    /// <returns>The address shape.</returns>
+    public static ModbusAddressShape Classify(JsonElement root)
+    {
+        if (root.ValueKind != JsonValueKind.Object) return ModbusAddressShape.NoAddress;
+        if (root.TryGetProperty("region", out _) && root.TryGetProperty("address", out _)) return ModbusAddressShape.Keys;
+        if (!root.TryGetProperty(AddressStringKey, out var s) || s.ValueKind == JsonValueKind.Null) return ModbusAddressShape.NoAddress;
+        if (s.ValueKind != JsonValueKind.String) return ModbusAddressShape.InvalidAddressString;
+        return string.IsNullOrWhiteSpace(s.GetString()) ? ModbusAddressShape.NoAddress : ModbusAddressShape.StringOnly;
+    }
+
+    /// <summary>Classifies a TagConfig JSON string (blank / malformed / non-object ⇒ <see cref="ModbusAddressShape.NoAddress"/>).</summary>
+    /// <param name="tagConfig">The TagConfig JSON.</param>
+    /// <returns>The address shape.</returns>
+    public static ModbusAddressShape Classify(string? tagConfig)
+    {
+        if (string.IsNullOrWhiteSpace(tagConfig)) return ModbusAddressShape.NoAddress;
+        try
+        {
+            using var doc = JsonDocument.Parse(tagConfig);
+            return Classify(doc.RootElement);
+        }
+        catch (JsonException) { return ModbusAddressShape.NoAddress; }
+    }
+
+    /// <summary>Resolves a TagConfig JSON string's address under one family.</summary>
+    /// <param name="tagConfig">The TagConfig JSON.</param>
+    /// <param name="family">The driver's PLC family.</param>
+    /// <param name="melsecSubFamily">The driver's MELSEC sub-family.</param>
+    /// <returns>The resolution.</returns>
+    public static ModbusAddressResolution Resolve(string? tagConfig, ModbusFamily family, MelsecFamily melsecSubFamily)
+    {
+        if (string.IsNullOrWhiteSpace(tagConfig))
+            return Refused(ModbusAddressShape.NoAddress, "Modbus TagConfig is blank — the tag names no address.");
+        try
+        {
+            using var doc = JsonDocument.Parse(tagConfig);
+            return Resolve(doc.RootElement, family, melsecSubFamily);
+        }
+        catch (JsonException)
+        {
+            return Refused(ModbusAddressShape.NoAddress, "Modbus TagConfig is not valid JSON — the tag will not resolve (BadNodeIdUnknown).");
+        }
+    }
+
+    /// <summary>
+    ///     Resolves the address of an object-rooted TagConfig under one family — the rule in the class remarks.
+    ///     Key reads are STRICT (a present-but-invalid <c>region</c> / <c>dataType</c> / <c>byteOrder</c>, or an
+    ///     <c>address</c> that is not an integer 0–65535, refuses the tag); a bit region's data type is coerced to
+    ///     <c>Bool</c> (pre-#741 editor blobs persisted <c>Int16</c> there and the old driver ignored it).
+    /// </summary>
+    /// <param name="root">The TagConfig root.</param>
+    /// <param name="family">The driver's PLC family.</param>
+    /// <param name="melsecSubFamily">The driver's MELSEC sub-family.</param>
+    /// <returns>The resolution.</returns>
+    public static ModbusAddressResolution Resolve(JsonElement root, ModbusFamily family, MelsecFamily melsecSubFamily)
+    {
+        var shape = Classify(root);
+        try
+        {
+            switch (shape)
+            {
+                case ModbusAddressShape.Keys:
+                    return ResolveKeys(root);
+                case ModbusAddressShape.StringOnly:
+                {
+                    var text = root.GetProperty(AddressStringKey).GetString()!.Trim();
+                    if (!ModbusAddressParser.TryParse(text, family, melsecSubFamily, out var parsed, out var error) || parsed is null)
+                        return Refused(shape, $"Modbus 'addressString' '{text}' does not parse under the {Describe(family, melsecSubFamily)} family ({error}) — the tag will not resolve (BadNodeIdUnknown).");
+                    return Resolved(shape, parsed.Region, parsed.Offset, parsed.DataType, parsed.ByteOrder,
+                        parsed.Bit ?? 0, parsed.StringLength, parsed.ArrayCount);
+                }
+                case ModbusAddressShape.InvalidAddressString:
+                    return Refused(shape, "Modbus TagConfig 'addressString' is not a string — the tag will not resolve (BadNodeIdUnknown).");
+                default:
+                    return Refused(shape, "Modbus TagConfig names no address: it needs 'region' + 'address' or an 'addressString' — the tag will not resolve (BadNodeIdUnknown).");
+            }
+        }
+        catch (FormatException) { return Refused(shape, "Modbus TagConfig address could not be read — the tag will not resolve (BadNodeIdUnknown)."); }
+        catch (InvalidOperationException) { return Refused(shape, "Modbus TagConfig address could not be read — the tag will not resolve (BadNodeIdUnknown)."); }
+    }
+
+    /// <summary>Whether the driver serves the blob's address under at least one family (the family-unaware gates' accept rule).</summary>
+    /// <param name="tagConfig">The TagConfig JSON.</param>
+    /// <returns><see langword="true"/> when some family resolves it.</returns>
+    public static bool ResolvesUnderAnyFamily(string? tagConfig)
+        => AllFamilies.Any(f => Resolve(tagConfig, f.Family, f.Sub).IsResolved);
+
+    /// <summary>
+    ///     Whether <paramref name="addressString"/> parses, under SOME family, to exactly the given address fields —
+    ///     i.e. the string still describes the keys beside it. Used by the CSV import to keep an exported pinned
+    ///     row's string through an unchanged round trip while dropping one a typed cell contradicts. It never
+    ///     decides the address (the keys do, by the rule above).
+    /// </summary>
+    /// <param name="addressString">The address string.</param>
+    /// <param name="region">The keys' region.</param>
+    /// <param name="address">The keys' offset.</param>
+    /// <param name="dataType">The keys' data type.</param>
+    /// <param name="byteOrder">The keys' byte order.</param>
+    /// <param name="bitIndex">The keys' bit index.</param>
+    /// <param name="stringLength">The keys' string length.</param>
+    /// <returns><see langword="true"/> when some family parses the string to those fields.</returns>
+    public static bool AddressStringDescribes(string? addressString, ModbusRegion region, int address, ModbusDataType dataType,
+        ModbusByteOrder byteOrder, int bitIndex, int stringLength)
+    {
+        if (string.IsNullOrWhiteSpace(addressString)) return false;
+        foreach (var (family, sub) in AllFamilies)
+        {
+            if (!ModbusAddressParser.TryParse(addressString.Trim(), family, sub, out var p, out _) || p is null) continue;
+            var parsedType = p.Region is ModbusRegion.Coils or ModbusRegion.DiscreteInputs ? ModbusDataType.Bool : p.DataType;
+            if (p.Region == region && p.Offset == address && parsedType == dataType && p.ByteOrder == byteOrder
+                && (p.Bit ?? 0) == bitIndex && p.StringLength == stringLength)
+                return true;
+        }
+        return false;
+    }
+
+    private static ModbusAddressResolution ResolveKeys(JsonElement root)
+    {
+        var addr = root.GetProperty("address");
+        if (addr.ValueKind != JsonValueKind.Number || !addr.TryGetInt32(out var address) || address < 0 || address > ushort.MaxValue)
+            return Refused(ModbusAddressShape.Keys,
+                $"value '{addr.GetRawText()}' for 'address' is not a Modbus register address (an integer 0–{ushort.MaxValue}); the tag will not resolve (BadNodeIdUnknown).");
+        if (!TagConfigJson.TryReadEnumStrict(root, "region", ModbusRegion.HoldingRegisters, out ModbusRegion region))
+            return Refused(ModbusAddressShape.Keys, TagConfigJson.DescribeInvalidEnum<ModbusRegion>(root, "region") ?? "invalid 'region'");
+        if (!TagConfigJson.TryReadEnumStrict(root, "dataType", ModbusTagDefinitionFactory.DefaultDataType(region), out ModbusDataType dataType))
+            return Refused(ModbusAddressShape.Keys, TagConfigJson.DescribeInvalidEnum<ModbusDataType>(root, "dataType") ?? "invalid 'dataType'");
+        if (!TagConfigJson.TryReadEnumStrict(root, "byteOrder", ModbusByteOrder.BigEndian, out ModbusByteOrder byteOrder))
+            return Refused(ModbusAddressShape.Keys, TagConfigJson.DescribeInvalidEnum<ModbusByteOrder>(root, "byteOrder") ?? "invalid 'byteOrder'");
+        // isArray / arrayLength: an array iff isArray:true AND arrayLength >= 1 (a 1-element array is valid).
+        var isArray = root.TryGetProperty("isArray", out var ia) && ia.ValueKind == JsonValueKind.True;
+        var arrayLength = ReadInt(root, "arrayLength");
+        return Resolved(ModbusAddressShape.Keys, region, address, dataType, byteOrder,
+            (byte)ReadInt(root, "bitIndex"), (ushort)ReadInt(root, "stringLength"), isArray && arrayLength >= 1 ? arrayLength : null);
+    }
+
+    private static ModbusAddressResolution Resolved(ModbusAddressShape shape, ModbusRegion region, int address, ModbusDataType dataType,
+        ModbusByteOrder byteOrder, int bitIndex, int stringLength, int? arrayCount)
+    {
+        // A bit region carries only Bool: coerce, never refuse (pre-#741 coil blobs persisted Int16).
+        if (region is ModbusRegion.Coils or ModbusRegion.DiscreteInputs) dataType = ModbusDataType.Bool;
+        return new ModbusAddressResolution(shape,
+            new ModbusResolvedAddress(shape, region, (ushort)address, dataType, byteOrder, (byte)bitIndex, (ushort)stringLength, arrayCount),
+            null);
+    }
+
+    private static ModbusAddressResolution Refused(ModbusAddressShape shape, string reason) => new(shape, null, reason);
+
+    private static string Describe(ModbusFamily family, MelsecFamily sub)
+        => family == ModbusFamily.MELSEC ? $"MELSEC {sub}" : family.ToString();
+
+    private static int ReadInt(JsonElement o, string name)
+        => o.TryGetProperty(name, out var e) && e.ValueKind == JsonValueKind.Number && e.TryGetInt32(out var v) ? v : 0;
+}
@@ -32,6 +32,25 @@ public static class ModbusTagDefinitionFactory
    /// <param name="def">The mapped definition when this returns <see langword="true"/>.</param>
    /// <returns><see langword="true"/> when <paramref name="tagConfig"/> is a valid Modbus address object.</returns>
    public static bool FromTagConfig(string tagConfig, string rawPath, out ModbusTagDefinition def)
+        => FromTagConfig(tagConfig, rawPath, ModbusFamily.Generic, MelsecFamily.Q_L_iQR, out def);
+
+    /// <summary>
+    ///     Family-aware overload — the call <c>ModbusDriver</c> makes with its own Family / MelsecSubFamily. WHICH
+    ///     address the blob names is decided by <see cref="ModbusTagAddressResolution"/> (the one authority shared
+    ///     with the deploy gate, the AdminUI editor model and the CSV import/export): <c>region</c> + <c>address</c>
+    ///     when both are present, else a string-only <c>addressString</c> resolved with the DRIVER's
+    ///     <paramref name="family"/> / <paramref name="melsecSubFamily"/> (refused when that family cannot parse it).
+    ///     This method adds only the non-address reads and guards (region/type compatibility, String length,
+    ///     BitInRegister index, writable, unitId, deadband, coalesceProhibited).
+    /// </summary>
+    /// <param name="tagConfig">The authored equipment-tag TagConfig JSON.</param>
+    /// <param name="rawPath">The tag's RawPath — becomes the definition's identity (<c>Name</c>).</param>
+    /// <param name="family">The driver's PLC family (from its <c>DriverConfig</c>).</param>
+    /// <param name="melsecSubFamily">The driver's MELSEC sub-family; consulted only for MELSEC.</param>
+    /// <param name="def">The mapped definition when this returns <see langword="true"/>.</param>
+    /// <returns><see langword="true"/> when <paramref name="tagConfig"/> is a valid Modbus address object.</returns>
+    public static bool FromTagConfig(string tagConfig, string rawPath, ModbusFamily family, MelsecFamily melsecSubFamily,
+        out ModbusTagDefinition def)
    {
        def = null!;
        if (string.IsNullOrWhiteSpace(tagConfig)) return false;
@@ -39,22 +58,24 @@ public static class ModbusTagDefinitionFactory
        {
            using var doc = JsonDocument.Parse(tagConfig);
            var root = doc.RootElement;
-            if (root.ValueKind != JsonValueKind.Object
-                || !root.TryGetProperty("region", out _)
-                || !root.TryGetProperty("address", out var addr))
-                return false;
-            if (addr.ValueKind != JsonValueKind.Number
-                || !addr.TryGetInt32(out var address)
-                || address < 0 || address > ushort.MaxValue)
-                return false;
-            // Strict enum reads: a present-but-invalid (typo'd) enum rejects the tag
-            // (→ BadNodeIdUnknown) instead of silently defaulting to a wrong-width Good.
-            if (!TagConfigJson.TryReadEnumStrict(root, "region", ModbusRegion.HoldingRegisters, out var region)) return false;
-            if (!TagConfigJson.TryReadEnumStrict(root, "dataType", ModbusDataType.Int16, out var dataType)) return false;
-            if (!TagConfigJson.TryReadEnumStrict(root, "byteOrder", ModbusByteOrder.BigEndian, out var byteOrder)) return false;
+            if (root.ValueKind != JsonValueKind.Object) return false;
+
+            // The address — region, offset, type, order, bit, length, count — comes from the ONE authority
+            // (ModbusTagAddressResolution: keys when both are present, else the addressString with this family).
+            var resolution = ModbusTagAddressResolution.Resolve(root, family, melsecSubFamily);
+            if (resolution.Address is not { } a) return false;
+            var region = a.Region;
+            var address = a.Address;
+            var dataType = a.DataType;
+            var byteOrder = a.ByteOrder;
+            var bitIndex = a.BitIndex;
+            var stringLength = a.StringLength;
+            var arrayCount = a.ArrayCount;
+            // Region/type compatibility. A bit region's dataType was already COERCED to Bool by the resolver
+            // (the pre-#741 editor persisted Int16 for coil tags and the old driver ignored it). A register
+            // region with Bool is refused: that pair never read (it threw out of the planner).
+            if (!IsRegionTypeCompatible(region, dataType)) return false;
            if (!TagConfigJson.TryReadEnumStrict(root, "stringByteOrder", ModbusStringByteOrder.HighByteFirst, out var stringByteOrder)) return false;
-            var bitIndex = (byte)ReadInt(root, "bitIndex");
-            var stringLength = (ushort)ReadInt(root, "stringLength");
            // Guard: String tags require StringLength >= 1. RegisterCount = (StringLength+1)/2,
            // so StringLength=0 → 0 registers → spec-illegal FC03/FC04 with quantity=0 → PLC
            // returns exception 03. Reject here so the driver surfaces BadNodeIdUnknown rather
@@ -63,14 +84,6 @@ public static class ModbusTagDefinitionFactory
            // Guard: BitInRegister tags require BitIndex 0–15. Shift by ≥ 16 on an int overflows
            // a ushort mask silently — reads always return false, writes have no effect.
            if (dataType == ModbusDataType.BitInRegister && bitIndex > 15) return false;
-            // isArray / arrayLength — optional keys authored by the typed Modbus tag editor.
-            // Canonical rule: a tag is an array iff isArray:true AND arrayLength >= 1.
-            // isArray:false (with any arrayLength) is scalar — the foundation materialises a
-            // scalar OPC UA node, so returning an array value would cause a shape mismatch.
-            // A 1-element array (isArray:true, arrayLength:1) IS valid and reads as short[1].
-            var isArray = ReadBool(root, "isArray");
-            var arrayLength = ReadInt(root, "arrayLength");
-            int? arrayCount = (isArray && arrayLength >= 1) ? arrayLength : null;
            // "writable" defaults to true when absent (today's value) — makes read-only equipment tags
            // authorable. Node-level authz remains the effective write gate.
            var writable = TagConfigJson.ReadWritable(root);
@@ -82,7 +95,7 @@ public static class ModbusTagDefinitionFactory
            var deadband = ReadOptionalDouble(root, "deadband");
            var coalesceProhibited = ReadBool(root, "coalesceProhibited");
            def = new ModbusTagDefinition(
-                Name: rawPath, Region: region, Address: (ushort)address, DataType: dataType,
+                Name: rawPath, Region: region, Address: address, DataType: dataType,
                Writable: writable, ByteOrder: byteOrder, BitIndex: bitIndex, StringLength: stringLength,
                StringByteOrder: stringByteOrder, WriteIdempotent: false,
                ArrayCount: arrayCount, Deadband: deadband, UnitId: unitId,
@@ -94,6 +107,49 @@ public static class ModbusTagDefinitionFactory
        catch (InvalidOperationException) { return false; }
    }

+    /// <summary>
+    ///     Family-unaware acceptance, for the gates that do not know the owning driver's family (the deploy
+    ///     gate's <see cref="Inspect"/>, CSV import, the AdminUI parse consult): accepts a blob SOME family
+    ///     resolves, so the gate is never stricter than the driver it guards. Blobs without an
+    ///     <c>addressString</c> behave exactly like <see cref="FromTagConfig(string,string,out ModbusTagDefinition)"/>.
+    /// </summary>
+    /// <param name="tagConfig">The authored equipment-tag TagConfig JSON.</param>
+    /// <param name="rawPath">The tag's RawPath.</param>
+    /// <param name="def">The definition under the first family that resolves it.</param>
+    /// <returns><see langword="true"/> when any family's driver would serve the tag.</returns>
+    public static bool FromTagConfigAnyFamily(string tagConfig, string rawPath, out ModbusTagDefinition def)
+    {
+        foreach (var (family, sub) in ModbusTagAddressResolution.AllFamilies)
+            if (FromTagConfig(tagConfig, rawPath, family, sub, out def)) return true;
+        def = null!;
+        return false;
+    }
+
+    /// <summary>
+    ///     The key the tag editor writes beside the resolved <c>region</c> / <c>address</c> (<c>"addressResolved": true</c>).
+    ///     Display / CSV state only — see <see cref="ModbusTagAddressResolution.AddressResolvedKey"/>.
+    /// </summary>
+    public const string AddressResolvedKey = ModbusTagAddressResolution.AddressResolvedKey;
+
+    /// <summary>The data type an authored tag gets when its <c>dataType</c> key is absent.</summary>
+    /// <param name="region">The tag's region.</param>
+    /// <returns><c>Bool</c> for Coils / DiscreteInputs, <c>Int16</c> for the register regions.</returns>
+    public static ModbusDataType DefaultDataType(ModbusRegion region)
+        => region is ModbusRegion.Coils or ModbusRegion.DiscreteInputs ? ModbusDataType.Bool : ModbusDataType.Int16;
+
+    /// <summary>
+    ///     Region/type compatibility, the one rule every authoring path and the driver share: Coils and
+    ///     DiscreteInputs carry only <c>Bool</c>; HoldingRegisters and InputRegisters carry every register
+    ///     type (including <c>BitInRegister</c>) but never <c>Bool</c>.
+    /// </summary>
+    /// <param name="region">The tag's region.</param>
+    /// <param name="dataType">The tag's data type.</param>
+    /// <returns><see langword="true"/> when the driver can read the pair.</returns>
+    public static bool IsRegionTypeCompatible(ModbusRegion region, ModbusDataType dataType)
+        => region is ModbusRegion.Coils or ModbusRegion.DiscreteInputs
+            ? dataType == ModbusDataType.Bool
+            : dataType != ModbusDataType.Bool;
+
    /// <summary>
    ///     Inverse of <see cref="FromTagConfig"/>: serialises a typed definition back to the camelCase
    ///     <c>TagConfig</c> JSON the mapper reads. Used by authoring paths (the Client CLI) that construct a
@@ -169,7 +225,7 @@ public static class ModbusTagDefinitionFactory

        // The accept gate: whatever the driver reads draws nothing. See the remarks. The RAW reference is
        // handed to the mapper — the driver reads the stored blob, not a trimmed copy of it.
-        if (FromTagConfig(reference, InspectionRawPath, out _)) return warnings;
+        if (FromTagConfigAnyFamily(reference, InspectionRawPath, out _)) return warnings;

        try
        {
@@ -210,6 +266,26 @@ public static class ModbusTagDefinitionFactory
    /// <param name="warnings">The list to append warnings to.</param>
    private static void DescribeRejection(JsonElement root, List<string> warnings)
    {
+        // Which part of the blob names the address is the resolver's call, never restated here.
+        switch (ModbusTagAddressResolution.Classify(root))
+        {
+            case ModbusAddressShape.InvalidAddressString:
+                warnings.Add("Modbus TagConfig 'addressString' is not a string — the tag will not resolve (BadNodeIdUnknown).");
+                return;
+            case ModbusAddressShape.StringOnly:
+            {
+                // String-only blob: the addressString is what the driver resolves (with its own family).
+                var addressText = root.GetProperty(ModbusTagAddressResolution.AddressStringKey).GetString()!.Trim();
+                if (!ModbusAddressParser.TryParse(addressText, out _, out var error))
+                    warnings.Add($"Modbus 'addressString' '{addressText}' does not parse under any PLC family ({error}) — "
+                                 + "the tag will not resolve (BadNodeIdUnknown).");
+                else
+                    warnings.Add($"Modbus 'addressString' '{addressText}' resolves to an unusable tag (check its type against "
+                                 + "the region) — the tag will not resolve (BadNodeIdUnknown).");
+                return;
+            }
+        }
+
        if (!root.TryGetProperty("region", out _))
        {
            warnings.Add(
@@ -247,7 +323,17 @@ public static class ModbusTagDefinitionFactory
        // Type-dependent guards. The byte/ushort NARROWING is part of the rule, not an accident of the
        // mapper: it reads `(byte)bitIndex` / `(ushort)stringLength`, so 256 is bit 0 and is ACCEPTED.
        // Describing the un-narrowed value here would call a blob invalid that the driver serves.
-        if (!TagConfigJson.TryReadEnumStrict(root, "dataType", ModbusDataType.Int16, out var dataType)) return;
+        var region = TagConfigJson.TryReadEnumStrict(root, "region", ModbusRegion.HoldingRegisters, out var r)
+            ? r : ModbusRegion.HoldingRegisters;
+        if (!TagConfigJson.TryReadEnumStrict(root, "dataType", DefaultDataType(region), out var dataType)) return;
+
+        // Only a register region with Bool is refused (a bit region with any type is coerced to Bool).
+        if (root.TryGetProperty("region", out _) && region is not (ModbusRegion.Coils or ModbusRegion.DiscreteInputs)
+            && !IsRegionTypeCompatible(region, dataType))
+        {
+            warnings.Add($"Modbus Bool tags only live in Coils / DiscreteInputs; a {region} tag must use a register type "
+                         + "(use BitInRegister for a bit of a register) — the tag is rejected (BadNodeIdUnknown).");
+        }

        if (dataType == ModbusDataType.String && (ushort)ReadInt(root, "stringLength") < 1)
        {
@@ -0,0 +1,17 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus;
+
+/// <summary>
+///     The device answered with well-framed data the tag's codec cannot represent (a non-BCD nibble in a
+///     BCD register, for example). The device is reachable, so this is a per-tag
+///     <c>BadDecodingError</c> with a once-per-tag Warning — never a comms fault, never a health write.
+/// </summary>
+public sealed class ModbusDecodeException : Exception
+{
+    /// <summary>Initializes a new instance of the <see cref="ModbusDecodeException"/> class.</summary>
+    /// <param name="message">A human-readable description.</param>
+    /// <param name="inner">The codec's own exception.</param>
+    public ModbusDecodeException(string message, Exception? inner = null)
+        : base(message, inner)
+    {
+    }
+}
@@ -78,22 +78,24 @@ public static class ModbusDriverFactoryExtensions
            Host = dto.Host!,
            Port = dto.Port ?? 502,
            UnitId = dto.UnitId ?? 1,
-            Timeout = TimeSpan.FromMilliseconds(dto.TimeoutMs ?? 2_000),
+            Timeout = Span(dto.TimeoutMs, dto.Timeout) ?? TimeSpan.FromSeconds(2),
            MaxRegistersPerRead = dto.MaxRegistersPerRead ?? 125,
            MaxRegistersPerWrite = dto.MaxRegistersPerWrite ?? 123,
            MaxCoilsPerRead = dto.MaxCoilsPerRead ?? 2000,
            UseFC15ForSingleCoilWrites = dto.UseFC15ForSingleCoilWrites ?? false,
            UseFC16ForSingleRegisterWrites = dto.UseFC16ForSingleRegisterWrites ?? false,
            DisableFC23 = dto.DisableFC23 ?? false,
+            UseFC23ForMultiRegisterWrites = dto.UseFC23ForMultiRegisterWrites ?? false,
            WriteOnChangeOnly = dto.WriteOnChangeOnly ?? false,
-            MaxReadGap = dto.MaxReadGap ?? 0,
+            MaxReadGap = dto.MaxReadGap ?? ModbusDriverOptions.DefaultMaxReadGap,
+            DisableReadCoalescing = dto.DisableReadCoalescing ?? false,
            Family = dto.Family is null ? ModbusFamily.Generic
                : ParseEnum<ModbusFamily>(dto.Family, "<driver-level>", driverInstanceId, "Family"),
            MelsecSubFamily = dto.MelsecSubFamily is null ? MelsecFamily.Q_L_iQR
                : ParseEnum<MelsecFamily>(dto.MelsecSubFamily, "<driver-level>", driverInstanceId, "MelsecSubFamily"),
            Transport = dto.Transport is null ? ModbusTransportMode.Tcp
                : ParseEnum<ModbusTransportMode>(dto.Transport, "<driver-level>", driverInstanceId, "Transport"),
-            AutoProhibitReprobeInterval = dto.AutoProhibitReprobeMs is { } reprobeMs ? TimeSpan.FromMilliseconds(reprobeMs) : null,
+            AutoProhibitReprobeInterval = Span(dto.AutoProhibitReprobeMs, dto.AutoProhibitReprobeInterval),
            AutoReconnect = dto.AutoReconnect ?? true,
            // v3: the deploy artifact (Wave C) populates rawTags with the cluster's authored raw Modbus
            // tags. The driver maps each RawTagEntry's TagConfig blob through ModbusTagDefinitionFactory
@@ -103,22 +105,22 @@ public static class ModbusDriverFactoryExtensions
            Probe = new ModbusProbeOptions
            {
                Enabled = dto.Probe?.Enabled ?? true,
-                Interval = TimeSpan.FromMilliseconds(dto.Probe?.IntervalMs ?? 5_000),
-                Timeout = TimeSpan.FromMilliseconds(dto.Probe?.TimeoutMs ?? 2_000),
+                Interval = Span(dto.Probe?.IntervalMs, dto.Probe?.Interval) ?? TimeSpan.FromSeconds(5),
+                Timeout = Span(dto.Probe?.TimeoutMs, dto.Probe?.Timeout) ?? TimeSpan.FromSeconds(2),
                ProbeAddress = dto.Probe?.ProbeAddress ?? 0,
            },
            KeepAlive = dto.KeepAlive is null ? new ModbusKeepAliveOptions() : new ModbusKeepAliveOptions
            {
                Enabled = dto.KeepAlive.Enabled ?? true,
-                Time = TimeSpan.FromMilliseconds(dto.KeepAlive.TimeMs ?? 30_000),
-                Interval = TimeSpan.FromMilliseconds(dto.KeepAlive.IntervalMs ?? 10_000),
+                Time = Span(dto.KeepAlive.TimeMs, dto.KeepAlive.Time) ?? TimeSpan.FromSeconds(30),
+                Interval = Span(dto.KeepAlive.IntervalMs, dto.KeepAlive.Interval) ?? TimeSpan.FromSeconds(10),
                RetryCount = dto.KeepAlive.RetryCount ?? 3,
            },
-            IdleDisconnectTimeout = dto.IdleDisconnectMs is { } ms ? TimeSpan.FromMilliseconds(ms) : null,
+            IdleDisconnectTimeout = Span(dto.IdleDisconnectMs, dto.IdleDisconnectTimeout),
            Reconnect = dto.Reconnect is null ? new ModbusReconnectOptions() : new ModbusReconnectOptions
            {
-                InitialDelay = TimeSpan.FromMilliseconds(dto.Reconnect.InitialDelayMs ?? 0),
-                MaxDelay = TimeSpan.FromMilliseconds(dto.Reconnect.MaxDelayMs ?? 30_000),
+                InitialDelay = Span(dto.Reconnect.InitialDelayMs, dto.Reconnect.InitialDelay) ?? TimeSpan.Zero,
+                MaxDelay = Span(dto.Reconnect.MaxDelayMs, dto.Reconnect.MaxDelay) ?? TimeSpan.FromSeconds(30),
                BackoffMultiplier = dto.Reconnect.BackoffMultiplier ?? 2.0,
            },
        };
@@ -126,6 +128,23 @@ public static class ModbusDriverFactoryExtensions
        return options;
    }

+    /// <summary>
+    ///     One timing knob, accepted in BOTH shapes the config can carry: the <c>*Ms</c> integer keys (CLI,
+    ///     seed data, hand-authored JSON) and the TimeSpan-string keys the AdminUI driver form emits — it
+    ///     serialises <see cref="ModbusDriverOptions"/> itself, so it writes <c>"timeout":"00:00:07"</c>, not
+    ///     <c>timeoutMs</c>. Before this every timing field on that form was silently ignored. The
+    ///     millisecond key wins when both are present; an unparseable TimeSpan string is ignored (the
+    ///     previous behaviour for these keys), never a reason to fail the driver.
+    /// </summary>
+    private static TimeSpan? Span(int? milliseconds, JsonElement? timeSpan)
+    {
+        if (milliseconds is { } ms) return TimeSpan.FromMilliseconds(ms);
+        if (timeSpan is { ValueKind: JsonValueKind.String } e
+            && TimeSpan.TryParse(e.GetString(), System.Globalization.CultureInfo.InvariantCulture, out var parsed))
+            return parsed;
+        return null;
+    }
+
    private static T ParseEnum<T>(string? raw, string? tagName, string driverInstanceId, string field) where T : struct, Enum
    {
        if (string.IsNullOrWhiteSpace(raw))
@@ -155,6 +174,8 @@ public static class ModbusDriverFactoryExtensions
        public byte? UnitId { get; init; }
        /// <summary>Gets or sets the timeout in milliseconds.</summary>
        public int? TimeoutMs { get; init; }
+        /// <summary>Gets or sets the timeout as a TimeSpan string (the AdminUI form's shape).</summary>
+        public JsonElement? Timeout { get; init; }
        /// <summary>Gets or sets the maximum number of registers per read operation.</summary>
        public ushort? MaxRegistersPerRead { get; init; }
        /// <summary>Gets or sets the maximum number of registers per write operation.</summary>
@@ -167,10 +188,14 @@ public static class ModbusDriverFactoryExtensions
        public bool? UseFC16ForSingleRegisterWrites { get; init; }
        /// <summary>Gets or sets a value indicating whether to disable function code 23.</summary>
        public bool? DisableFC23 { get; init; }
+        /// <summary>Gets or sets a value indicating whether multi-register writes opt in to FC23 write + read-back.</summary>
+        public bool? UseFC23ForMultiRegisterWrites { get; init; }
        /// <summary>Gets or sets a value indicating whether to write only on change.</summary>
        public bool? WriteOnChangeOnly { get; init; }
        /// <summary>Gets or sets the maximum gap between register addresses for coalescing.</summary>
        public ushort? MaxReadGap { get; init; }
+        /// <summary>Gets or sets a value indicating whether block-read coalescing is turned off entirely.</summary>
+        public bool? DisableReadCoalescing { get; init; }
        /// <summary>Gets or sets the Modbus family type.</summary>
        public string? Family { get; init; }
        /// <summary>Gets or sets the Melsec subfamily.</summary>
@@ -179,6 +204,8 @@ public static class ModbusDriverFactoryExtensions
        public string? Transport { get; init; }
        /// <summary>Gets or sets the automatic prohibition reprobei interval in milliseconds.</summary>
        public int? AutoProhibitReprobeMs { get; init; }
+        /// <summary>Gets or sets the re-probe interval as a TimeSpan string (the AdminUI form's shape).</summary>
+        public JsonElement? AutoProhibitReprobeInterval { get; init; }
        /// <summary>Gets or sets a value indicating whether automatic reconnection is enabled.</summary>
        public bool? AutoReconnect { get; init; }
        /// <summary>Gets or sets the authored raw tags (RawPath + TagConfig blob + WriteIdempotent) the
@@ -191,6 +218,8 @@ public static class ModbusDriverFactoryExtensions
        public ModbusKeepAliveDto? KeepAlive { get; init; }
        /// <summary>Gets or sets the idle disconnect timeout in milliseconds.</summary>
        public int? IdleDisconnectMs { get; init; }
+        /// <summary>Gets or sets the idle disconnect timeout as a TimeSpan string (the AdminUI form's shape).</summary>
+        public JsonElement? IdleDisconnectTimeout { get; init; }
        /// <summary>Gets or sets the reconnect configuration.</summary>
        public ModbusReconnectDto? Reconnect { get; init; }
    }
@@ -203,6 +232,10 @@ public static class ModbusDriverFactoryExtensions
        public int? TimeMs { get; init; }
        /// <summary>Gets or sets the keep-alive interval in milliseconds.</summary>
        public int? IntervalMs { get; init; }
+        /// <summary>Gets or sets the keep-alive time as a TimeSpan string (the AdminUI form's shape).</summary>
+        public JsonElement? Time { get; init; }
+        /// <summary>Gets or sets the keep-alive interval as a TimeSpan string (the AdminUI form's shape).</summary>
+        public JsonElement? Interval { get; init; }
        /// <summary>Gets or sets the retry count.</summary>
        public int? RetryCount { get; init; }
    }
@@ -213,6 +246,10 @@ public static class ModbusDriverFactoryExtensions
        public int? InitialDelayMs { get; init; }
        /// <summary>Gets or sets the maximum reconnect delay in milliseconds.</summary>
        public int? MaxDelayMs { get; init; }
+        /// <summary>Gets or sets the initial reconnect delay as a TimeSpan string (the AdminUI form's shape).</summary>
+        public JsonElement? InitialDelay { get; init; }
+        /// <summary>Gets or sets the maximum reconnect delay as a TimeSpan string (the AdminUI form's shape).</summary>
+        public JsonElement? MaxDelay { get; init; }
        /// <summary>Gets or sets the backoff multiplier for exponential reconnect delays.</summary>
        public double? BackoffMultiplier { get; init; }
    }
@@ -225,6 +262,10 @@ public static class ModbusDriverFactoryExtensions
        public int? IntervalMs { get; init; }
        /// <summary>Gets or sets the probe timeout in milliseconds.</summary>
        public int? TimeoutMs { get; init; }
+        /// <summary>Gets or sets the probe interval as a TimeSpan string (the AdminUI form's shape).</summary>
+        public JsonElement? Interval { get; init; }
+        /// <summary>Gets or sets the probe timeout as a TimeSpan string (the AdminUI form's shape).</summary>
+        public JsonElement? Timeout { get; init; }
        /// <summary>Gets or sets the probe register address.</summary>
        public ushort? ProbeAddress { get; init; }
    }
@@ -93,9 +93,10 @@ public static class ModbusRtuFraming
            // Exception frame: excCode(1) + CRC(2).
            trailing = 1 + 2;
        }
-        else if (fc is 0x01 or 0x02 or 0x03 or 0x04)
+        else if (fc is 0x01 or 0x02 or 0x03 or 0x04 or 0x17)
        {
-            // Read response: byteCount(1) then byteCount data bytes + CRC(2).
+            // Read response (and FC23 Read/Write Multiple, whose reply is a read): byteCount(1) then
+            // byteCount data bytes + CRC(2).
            var bc = new byte[1];
            await ReadExactlyAsync(stream, bc, ct).ConfigureAwait(false);
            var byteCount = bc[0];
@@ -105,9 +106,9 @@ public static class ModbusRtuFraming
        }
        else
        {
-            // Fixed 4-byte echo: correct for the write FCs this driver emits (05/06/0F/10). A future
-            // variable-length response FC outside 01-04 (e.g. FC23) would be mis-sized here and
-            // surface as a desync — revisit the FC-shape table if the driver starts emitting one.
+            // Fixed 4-byte echo: correct for the write FCs this driver emits (05/06/0F/10). FC23 is
+            // variable-length and handled above; any NEW variable-length response FC must be added there
+            // or it is mis-sized here and surfaces as a desync.
            trailing = 4 + 2;
        }

@@ -46,7 +46,7 @@ public sealed class ModbusRtuOverTcpTransport : IModbusTransport
    private readonly Stream? _testStream;
    private readonly TimeSpan _timeout;
    private readonly SemaphoreSlim _gate = new(1, 1);
-    private bool _disposed;
+    private int _disposed;

    /// <summary>Initializes a new instance of the <see cref="ModbusRtuOverTcpTransport"/> class.</summary>
    /// <param name="host">The host address or hostname of the Modbus gateway.</param>
@@ -90,8 +90,8 @@ public sealed class ModbusRtuOverTcpTransport : IModbusTransport
    /// <inheritdoc />
    public async Task<byte[]> SendAsync(byte unitId, byte[] pdu, CancellationToken ct)
    {
-        if (_disposed) throw new ObjectDisposedException(nameof(ModbusRtuOverTcpTransport));
-        if (CurrentStream is null) throw new InvalidOperationException("Transport not connected");
+        if (Volatile.Read(ref _disposed) != 0) throw new ObjectDisposedException(nameof(ModbusRtuOverTcpTransport));
+        if (_life is null && _testStream is null) throw new InvalidOperationException("Transport not connected");

        // Single-flight: RTU carries no transaction id, so at most one transaction may be on the bus
        // at a time — serialise every send/receive under the gate.
@@ -101,11 +101,14 @@ public sealed class ModbusRtuOverTcpTransport : IModbusTransport
            // Proactive idle-disconnect (real socket only): if the socket has been quiet longer than
            // the configured threshold, tear it down + reconnect before this PDU lands. Defends
            // against silent NAT / firewall reaping.
-            if (_life is not null && _life.ShouldReconnectForIdle())
-            {
+            if (_life is not null && _life.Stream is not null && _life.ShouldReconnectForIdle())
                await _life.TearDownAsync().ConfigureAwait(false);
-                await _life.ConnectWithBackoffAsync(ct).ConfigureAwait(false);
-            }
+
+            // Self-heal (real socket only): a socket torn down by an earlier failure is re-dialled here,
+            // once, throttled by the backoff window — same contract as ModbusTcpTransport.
+            var freshlyConnected = _life is not null && _life.Stream is null;
+            if (freshlyConnected)
+                await _life!.EnsureConnectedAsync(ct).ConfigureAwait(false);

            try
            {
@@ -113,14 +116,16 @@ public sealed class ModbusRtuOverTcpTransport : IModbusTransport
                _life?.MarkSuccess();
                return result;
            }
-            catch (Exception ex) when (_life is not null && _life.AutoReconnect && ModbusSocketLifecycle.IsSocketLevelFailure(ex))
+            catch (Exception ex) when (!freshlyConnected && _life is not null && _life.AutoReconnect
+                                       && !ct.IsCancellationRequested
+                                       && ModbusSocketLifecycle.IsSocketLevelFailure(ex))
            {
-                // Mid-transaction drop: tear down the dead socket, reconnect (with backoff if
-                // configured), resend. Single retry — a second failure propagates so health/status
-                // reflect reality. Never reached in the ForTest seam (a raw injected stream has no
-                // lifecycle to reconnect).
+                // Mid-transaction drop: tear down the dead socket, make ONE throttled reconnect attempt
+                // (never a sleep inside the gate), resend. Single retry — a second failure propagates so
+                // health/status reflect reality. Never reached in the ForTest seam (a raw injected stream
+                // has no lifecycle to reconnect).
                await _life.TearDownAsync().ConfigureAwait(false);
-                await _life.ConnectWithBackoffAsync(ct).ConfigureAwait(false);
+                await _life.EnsureConnectedAsync(ct).ConfigureAwait(false);
                var result = await SendOnceAsync(unitId, pdu, ct).ConfigureAwait(false);
                _life.MarkSuccess();
                return result;
@@ -182,9 +187,8 @@ public sealed class ModbusRtuOverTcpTransport : IModbusTransport
    /// <returns>A task that represents the asynchronous operation.</returns>
    public async ValueTask DisposeAsync()
    {
-        if (_disposed) return;
-        _disposed = true;
+        if (Interlocked.Exchange(ref _disposed, 1) != 0) return;
        if (_life is not null) await _life.DisposeAsync().ConfigureAwait(false);
-        _gate.Dispose();
+        // _gate is deliberately NOT disposed: a SendAsync still in flight at teardown releases it in its finally.
    }
 }
@@ -4,8 +4,8 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus;

 /// <summary>
 ///     Owns the raw TCP socket lifecycle shared by every Modbus-over-TCP transport (MBAP and
-///     RTU-over-TCP alike): the IPv4-preference connect, OS-level keep-alive, geometric-backoff
-///     reconnect, idle-disconnect tracking, and teardown. It exposes the current
+///     RTU-over-TCP alike): the IPv4-preference connect, OS-level keep-alive, throttled
+///     reconnect (one attempt per geometric-backoff window), idle-disconnect tracking, and teardown. It exposes the current
 ///     <see cref="NetworkStream"/> so the composing transport can drive its own framing on top —
 ///     the lifecycle knows nothing about MBAP / RTU wire layout.
 /// </summary>
@@ -14,7 +14,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus;
 ///         Extracted verbatim from <see cref="ModbusTcpTransport"/> so the connect / reconnect /
 ///         keep-alive / idle behaviour is written once and composed by both transports. The
 ///         constructor is connection-free — all socket I/O happens in <see cref="ConnectAsync"/> /
-///         <see cref="ConnectWithBackoffAsync"/>.
+///         <see cref="EnsureConnectedAsync"/> (one throttled attempt per call — never a sleep loop).
 ///     </para>
 ///     <para>
 ///         Why keep-alive matters for DL205/DL260: the AutomationDirect H2-ECOM100 does NOT send
@@ -37,6 +37,9 @@ public sealed class ModbusSocketLifecycle : IAsyncDisposable
    private NetworkStream? _stream;
    private DateTime _lastSuccessUtc = DateTime.UtcNow;

+    /// <summary>Monotonic millisecond clock for the reconnect throttle (test seam).</summary>
+    internal Func<long> NowMs { get; set; } = () => Environment.TickCount64;
+
    /// <summary>Initializes a new instance of the <see cref="ModbusSocketLifecycle"/> class.</summary>
    /// <param name="host">The host address or hostname of the Modbus server.</param>
    /// <param name="port">The TCP port of the Modbus server.</param>
@@ -71,63 +74,116 @@ public sealed class ModbusSocketLifecycle : IAsyncDisposable
    /// <returns>A task representing the asynchronous connection operation.</returns>
    public async Task ConnectAsync(CancellationToken ct)
    {
-        // Resolve the host explicitly + prefer IPv4. .NET's TcpClient default-constructor is
-        // dual-stack (IPv6 first, fallback to IPv4) — but most Modbus TCP devices (PLCs and
-        // simulators like pymodbus) bind 0.0.0.0 only, so the IPv6 attempt times out and we
-        // burn the entire ConnectAsync budget before even trying IPv4. Resolving first +
-        // dialing the IPv4 address directly sidesteps that.
-        var addresses = await System.Net.Dns.GetHostAddressesAsync(_host, ct).ConfigureAwait(false);
-        var ipv4 = System.Linq.Enumerable.FirstOrDefault(addresses,
-            a => a.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork);
-        var target = ipv4 ?? (addresses.Length > 0 ? addresses[0] : System.Net.IPAddress.Loopback);
-
-        _client = new TcpClient(target.AddressFamily);
-        EnableKeepAlive(_client, _keepAlive);
+        // A previous socket (failed, torn down or idle-reaped) is released FIRST: overwriting _client
+        // used to strand the old TcpClient for the finalizer — up to nine per backoff loop.
+        ThrowIfDisposed();
+        await TearDownAsync().ConfigureAwait(false);

+        // DNS resolution runs under the same per-op deadline as the TCP connect: an unresolvable or
+        // slow resolver must not hold the transport gate for the OS resolver's own (much longer) timeout.
        using var cts = CancellationTokenSource.CreateLinkedTokenSource(ct);
        cts.CancelAfter(_timeout);
-        await _client.ConnectAsync(target, _port, cts.Token).ConfigureAwait(false);
-        _stream = _client.GetStream();
-        _lastSuccessUtc = DateTime.UtcNow;
+        TcpClient? client = null;
+        try
+        {
+            // Resolve the host explicitly + prefer IPv4. .NET's TcpClient default-constructor is
+            // dual-stack (IPv6 first, fallback to IPv4) — but most Modbus TCP devices (PLCs and
+            // simulators like pymodbus) bind 0.0.0.0 only, so the IPv6 attempt times out and we
+            // burn the entire ConnectAsync budget before even trying IPv4. Resolving first +
+            // dialing the IPv4 address directly sidesteps that.
+            var addresses = await System.Net.Dns.GetHostAddressesAsync(_host, cts.Token).ConfigureAwait(false);
+            var ipv4 = System.Linq.Enumerable.FirstOrDefault(addresses,
+                a => a.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork);
+            var target = ipv4 ?? (addresses.Length > 0 ? addresses[0] : System.Net.IPAddress.Loopback);
+
+            client = new TcpClient(target.AddressFamily);
+            EnableKeepAlive(client, _keepAlive);
+            await client.ConnectAsync(target, _port, cts.Token).ConfigureAwait(false);
+            ThrowIfDisposed(); // disposed while dialling — the finally releases the fresh client
+            _stream = client.GetStream();
+            _client = client;
+            client = null; // ownership transferred
+            if (Volatile.Read(ref _disposed) != 0)
+            {
+                // A DisposeAsync that ran between the check above and the publish has already torn down;
+                // tear the fresh socket down ourselves so it is never stranded for the finalizer.
+                await TearDownAsync().ConfigureAwait(false);
+                throw new ObjectDisposedException(nameof(ModbusSocketLifecycle));
+            }
+            _lastSuccessUtc = DateTime.UtcNow;
+        }
+        catch (OperationCanceledException) when (!ct.IsCancellationRequested)
+        {
+            // The per-op deadline, not the caller: normalise to a socket-level failure so every
+            // classifier treats a connect timeout as a comms fault.
+            throw new ModbusTransportUnavailableException(
+                $"Modbus connect to {_host}:{_port} timed out after {_timeout.TotalMilliseconds:0}ms");
+        }
+        finally
+        {
+            // A failed attempt disposes its own client — never leave it for the finalizer.
+            client?.Dispose();
+        }
    }

+    // Reconnect throttle state. Guarded by the composing transport's single-flight gate (every caller of
+    // EnsureConnectedAsync holds it), so no extra lock is needed.
+    private long _connectNotBeforeMs;
+    private TimeSpan _failureDelay = TimeSpan.Zero;
+
    /// <summary>
-    ///     Connect attempt with the configured geometric backoff. The first attempt fires after
-    ///     <see cref="ModbusReconnectOptions.InitialDelay"/> (default zero — immediate); each
-    ///     subsequent attempt sleeps for the previous delay times <c>BackoffMultiplier</c>,
-    ///     capped at <c>MaxDelay</c>. Caller's cancellation token aborts the loop.
+    ///     Ensures a live socket for the next transaction with AT MOST ONE connect attempt, throttled by the
+    ///     configured geometric backoff: after a failed attempt, calls inside the backoff window fail fast
+    ///     with <see cref="ModbusTransportUnavailableException"/> and never dial. The window starts at
+    ///     <see cref="ModbusReconnectOptions.InitialDelay"/> (floored at 1 s) and grows by
+    ///     <c>BackoffMultiplier</c> per consecutive failure up to <c>MaxDelay</c>; a successful connect
+    ///     resets it. Never sleeps — the composing transport calls it inside its gate, and a sleep there
+    ///     used to queue every read, write and probe behind one dead socket for up to ~81 s.
    /// </summary>
    /// <param name="ct">A cancellation token to observe for cancellation.</param>
-    /// <returns>A task representing the asynchronous reconnect operation.</returns>
-    public async Task ConnectWithBackoffAsync(CancellationToken ct)
+    /// <returns>A task that completes when a socket is live.</returns>
+    /// <exception cref="ModbusTransportUnavailableException">Auto-reconnect is off, or the call is inside the backoff window.</exception>
+    public async Task EnsureConnectedAsync(CancellationToken ct)
    {
-        var delay = _reconnect.InitialDelay;
-        var attempt = 0;
-        while (true)
+        if (_stream is not null) return;
+        if (!_autoReconnect)
+            throw new ModbusTransportUnavailableException(
+                $"Modbus transport to {_host}:{_port} is not connected and auto-reconnect is disabled");
+
+        var now = NowMs();
+        if (now < _connectNotBeforeMs)
+            throw new ModbusTransportUnavailableException(
+                $"Modbus reconnect to {_host}:{_port} throttled for another {_connectNotBeforeMs - now}ms after a failed connect");
+
+        try
        {
-            if (delay > TimeSpan.Zero)
-                await Task.Delay(delay, ct).ConfigureAwait(false);
-            try
-            {
-                await ConnectAsync(ct).ConfigureAwait(false);
-                return;
-            }
-            catch (Exception ex) when (IsSocketLevelFailure(ex) && _autoReconnect)
-            {
-                attempt++;
-                // Geometric growth, capped. Use Math.Min on ticks so we don't overflow with
-                // pathological multipliers / long deployments.
-                var nextTicks = (long)(Math.Max(delay.Ticks, TimeSpan.FromMilliseconds(100).Ticks) * _reconnect.BackoffMultiplier);
-                delay = TimeSpan.FromTicks(Math.Min(nextTicks, _reconnect.MaxDelay.Ticks));
-                if (attempt >= 10)
-                {
-                    // Bail after 10 attempts to surface persistent failure to the caller. With
-                    // the default backoff (1s base, 2.0x mult, 30s cap) this is roughly 4 minutes
-                    // of attempts; with InitialDelay=0 it's immediate up to the same cap.
-                    throw;
-                }
-            }
+            await ConnectAsync(ct).ConfigureAwait(false);
+            _failureDelay = TimeSpan.Zero;
+            _connectNotBeforeMs = 0;
        }
+        catch (Exception) when (!ct.IsCancellationRequested)
+        {
+            _failureDelay = NextDelay(_failureDelay);
+            _connectNotBeforeMs = NowMs() + (long)_failureDelay.TotalMilliseconds;
+            throw;
+        }
+    }
+
+    /// <summary>Minimum reconnect window after a failed connect — a dead device is dialled at most once per second.</summary>
+    private static readonly TimeSpan MinReconnectWindow = TimeSpan.FromSeconds(1);
+
+    private TimeSpan NextDelay(TimeSpan previous)
+    {
+        if (previous <= TimeSpan.Zero)
+        {
+            var first = _reconnect.InitialDelay > MinReconnectWindow ? _reconnect.InitialDelay : MinReconnectWindow;
+            return first < _reconnect.MaxDelay ? first : _reconnect.MaxDelay > TimeSpan.Zero ? _reconnect.MaxDelay : first;
+        }
+        // Geometric growth, capped. Math.Min on ticks so a pathological multiplier cannot overflow.
+        var multiplier = _reconnect.BackoffMultiplier >= 1.0 ? _reconnect.BackoffMultiplier : 1.0;
+        var nextTicks = previous.Ticks * multiplier;
+        var cap = _reconnect.MaxDelay > TimeSpan.Zero ? _reconnect.MaxDelay.Ticks : long.MaxValue;
+        return TimeSpan.FromTicks(nextTicks >= cap ? cap : (long)nextTicks);
    }

    /// <summary>
@@ -211,11 +267,16 @@ public sealed class ModbusSocketLifecycle : IAsyncDisposable
    /// <returns>A task that represents the asynchronous operation.</returns>
    public async ValueTask DisposeAsync()
    {
-        try
-        {
-            if (_stream is not null) await _stream.DisposeAsync().ConfigureAwait(false);
-        }
-        catch { /* best-effort */ }
-        _client?.Dispose();
+        // Latch first: a SendAsync still in flight (the driver tearing down under it) must not reconnect
+        // a fresh socket after this point — ConnectAsync checks the latch both before and after dialling.
+        Volatile.Write(ref _disposed, 1);
+        await TearDownAsync().ConfigureAwait(false);
+    }
+
+    private int _disposed;
+
+    private void ThrowIfDisposed()
+    {
+        if (Volatile.Read(ref _disposed) != 0) throw new ObjectDisposedException(nameof(ModbusSocketLifecycle));
    }
 }
@@ -36,7 +36,7 @@ public sealed class ModbusTcpTransport : IModbusTransport
    private readonly TimeSpan _timeout;
    private readonly SemaphoreSlim _gate = new(1, 1);
    private ushort _nextTx;
-    private bool _disposed;
+    private int _disposed;

    /// <summary>Initializes a new instance of the <see cref="ModbusTcpTransport"/> class.</summary>
    /// <param name="host">The host address or hostname of the Modbus server.</param>
@@ -56,14 +56,16 @@ public sealed class ModbusTcpTransport : IModbusTransport
        _life = new ModbusSocketLifecycle(host, port, timeout, autoReconnect, keepAlive, idleDisconnect, reconnect);
    }

+    /// <summary>The socket lifecycle this transport composes (test seam for its clock).</summary>
+    internal ModbusSocketLifecycle Lifecycle => _life;
+
    /// <inheritdoc />
    public Task ConnectAsync(CancellationToken ct) => _life.ConnectAsync(ct);

    /// <inheritdoc />
    public async Task<byte[]> SendAsync(byte unitId, byte[] pdu, CancellationToken ct)
    {
-        if (_disposed) throw new ObjectDisposedException(nameof(ModbusTcpTransport));
-        if (_life.Stream is null) throw new InvalidOperationException("Transport not connected");
+        if (Volatile.Read(ref _disposed) != 0) throw new ObjectDisposedException(nameof(ModbusTcpTransport));

        await _gate.WaitAsync(ct).ConfigureAwait(false);
        try
@@ -72,11 +74,16 @@ public sealed class ModbusTcpTransport : IModbusTransport
            // threshold, tear it down + reconnect before this PDU lands. Defends against silent
            // NAT / firewall reaping where the socket looks alive locally but the upstream side
            // dropped it minutes ago.
-            if (_life.ShouldReconnectForIdle())
-            {
+            if (_life.Stream is not null && _life.ShouldReconnectForIdle())
                await _life.TearDownAsync().ConfigureAwait(false);
-                await _life.ConnectWithBackoffAsync(ct).ConfigureAwait(false);
-            }
+
+            // Self-heal: a socket torn down by an earlier failure (two lost replies in a row, a refused
+            // reconnect) is re-dialled HERE, once, throttled by the backoff window. This used to throw
+            // "Transport not connected" before the gate, so the transport never recovered on its own and
+            // every call failed fast until the 90 s comms-loss watchdog re-initialised the whole driver.
+            var freshlyConnected = _life.Stream is null;
+            if (freshlyConnected)
+                await _life.EnsureConnectedAsync(ct).ConfigureAwait(false);

            try
            {
@@ -84,13 +91,16 @@ public sealed class ModbusTcpTransport : IModbusTransport
                _life.MarkSuccess();
                return result;
            }
-            catch (Exception ex) when (_life.AutoReconnect && ModbusSocketLifecycle.IsSocketLevelFailure(ex))
+            catch (Exception ex) when (!freshlyConnected && _life.AutoReconnect
+                                       && !ct.IsCancellationRequested
+                                       && ModbusSocketLifecycle.IsSocketLevelFailure(ex))
            {
-                // Mid-transaction drop: tear down the dead socket, reconnect (with backoff if
-                // configured), resend. Single retry — if it fails again, let it propagate so
-                // health/status reflect reality.
+                // Mid-transaction drop on a socket that had been live: tear down the dead socket, make ONE
+                // throttled reconnect attempt (never a sleep inside the gate), resend. Single retry — if it
+                // fails again, let it propagate so health/status reflect reality. A socket this call just
+                // dialled is not retried: it proved nothing about a stale connection.
                await _life.TearDownAsync().ConfigureAwait(false);
-                await _life.ConnectWithBackoffAsync(ct).ConfigureAwait(false);
+                await _life.EnsureConnectedAsync(ct).ConfigureAwait(false);
                var result = await SendOnceAsync(unitId, pdu, ct).ConfigureAwait(false);
                _life.MarkSuccess();
                return result;
@@ -162,10 +172,22 @@ public sealed class ModbusTcpTransport : IModbusTransport
            var respPdu = new byte[respLen - 1];
            await ReadExactlyAsync(stream, respPdu, cts.Token).ConfigureAwait(false);

+            // Length check before indexing: a PDU must carry at least its function code, and an exception
+            // PDU its exception code too. Indexing past the end used to throw IndexOutOfRangeException —
+            // not an IOException, so no teardown/retry, and a malformed reply read as a driver bug.
+            if (respPdu.Length < 1)
+                throw new ModbusTransportDesyncException(
+                    ModbusTransportDesyncException.DesyncReason.TruncatedFrame,
+                    "Modbus response carried no PDU (MBAP length 1)");
+
            // Exception PDU: function code has high bit set. This is a well-formed protocol-level
            // error — the socket is still coherent, so it MUST propagate without teardown.
            if ((respPdu[0] & 0x80) != 0)
            {
+                if (respPdu.Length < 2)
+                    throw new ModbusTransportDesyncException(
+                        ModbusTransportDesyncException.DesyncReason.TruncatedFrame,
+                        $"Modbus exception response fc=0x{respPdu[0]:X2} carried no exception code");
                var fc = (byte)(respPdu[0] & 0x7F);
                var ex = respPdu[1];
                throw new ModbusException(fc, ex, $"Modbus exception fc={fc} code={ex}");
@@ -206,9 +228,8 @@ public sealed class ModbusTcpTransport : IModbusTransport
    /// <returns>A task that represents the asynchronous operation.</returns>
    public async ValueTask DisposeAsync()
    {
-        if (_disposed) return;
-        _disposed = true;
+        if (Interlocked.Exchange(ref _disposed, 1) != 0) return;
        await _life.DisposeAsync().ConfigureAwait(false);
-        _gate.Dispose();
+        // _gate is deliberately NOT disposed: a SendAsync still in flight at teardown releases it in its finally.
    }
 }
@@ -0,0 +1,23 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus;
+
+/// <summary>
+///     Raised when a Modbus transport has no live socket and cannot get one for this call: the one
+///     in-gate connect attempt failed, the reconnect is inside its backoff window, or auto-reconnect is
+///     disabled. It says the ENDPOINT is unreachable, so the driver fails the rest of the batch fast
+///     instead of paying the same failure once per tag.
+/// </summary>
+/// <remarks>
+///     Derives from <see cref="IOException"/> so every existing socket-level classifier
+///     (<c>ModbusSocketLifecycle.IsSocketLevelFailure</c>, the driver's comms-fault mapping) treats it as
+///     a communication failure without extra plumbing.
+/// </remarks>
+public sealed class ModbusTransportUnavailableException : IOException
+{
+    /// <summary>Initializes a new instance of the <see cref="ModbusTransportUnavailableException"/> class.</summary>
+    /// <param name="message">A human-readable description.</param>
+    /// <param name="inner">The originating exception, if any.</param>
+    public ModbusTransportUnavailableException(string message, Exception? inner = null)
+        : base(message, inner)
+    {
+    }
+}
@@ -0,0 +1,21 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus;
+
+/// <summary>
+///     The driver refused a write BEFORE anything reached the wire (wrong array length, a payload over
+///     <c>MaxRegistersPerWrite</c>, an unsupported shape). Carries the OPC UA status the write returns;
+///     it never touches driver health — nothing was sent.
+/// </summary>
+public sealed class ModbusWriteRefusedException : Exception
+{
+    /// <summary>Initializes a new instance of the <see cref="ModbusWriteRefusedException"/> class.</summary>
+    /// <param name="statusCode">The OPC UA status the write returns.</param>
+    /// <param name="message">A human-readable description.</param>
+    public ModbusWriteRefusedException(uint statusCode, string message)
+        : base(message)
+    {
+        StatusCode = statusCode;
+    }
+
+    /// <summary>Gets the OPC UA status the write returns.</summary>
+    public uint StatusCode { get; }
+}
@@ -149,6 +149,16 @@ internal sealed class MqttBrowseSession : IRebirthCapableBrowseSession
    /// </summary>
    private static readonly UTF8Encoding Utf8Strict = new(encoderShouldEmitUTF8Identifier: false, throwOnInvalidBytes: true);

+    /// <summary>
+    ///     Ceiling on the rebirth request's wait, below the AdminUI's 20 s <c>BrowserSessionService.PerCallTimeout</c>
+    ///     (review minor 4): a configured window above it could never take effect there, and a rebirth aimed at an
+    ///     offline edge node must not hold the operator's button for the whole window.
+    /// </summary>
+    internal static readonly TimeSpan MaxRebirthWait = TimeSpan.FromSeconds(15);
+
+    /// <summary>The quiet spell that ends a rebirth request's wait once its births have started arriving.</summary>
+    private static readonly TimeSpan RebirthQuietInterval = TimeSpan.FromMilliseconds(500);
+
    /// <summary>Bound on the courtesy DISCONNECT issued at dispose — teardown never hangs on a dead broker.</summary>
    private static readonly TimeSpan DisconnectTimeout = TimeSpan.FromSeconds(5);

@@ -174,6 +184,7 @@ internal sealed class MqttBrowseSession : IRebirthCapableBrowseSession
    private readonly ConcurrentQueue<string> _publishedTopics = new();

    private int _disposed;
+    private long _birthCount;
    private long _lastUsedTicksUtc = DateTime.UtcNow.Ticks;
    private int _nodeCount;
    private int _oversized;
@@ -195,9 +206,16 @@ internal sealed class MqttBrowseSession : IRebirthCapableBrowseSession
    /// <param name="client">The connected MQTT client; disconnected and disposed by <see cref="DisposeAsync"/>.</param>
    /// <param name="logger">Optional logger; never receives credentials or payload bodies.</param>
    /// <param name="nodeCap">Cap on recorded nodes; defaults to <see cref="DefaultNodeCap"/>.</param>
-    internal MqttBrowseSession(MqttMode mode, IMqttClient? client, ILogger? logger, int nodeCap = DefaultNodeCap)
+    /// <param name="birthWindow">
+    ///     The Sparkplug birth-observation window: how long <see cref="RequestRebirthAsync"/> waits for the
+    ///     births it asked for. <see cref="TimeSpan.Zero"/> (the test default) returns as soon as the NCMDs
+    ///     are published.
+    /// </param>
+    internal MqttBrowseSession(
+        MqttMode mode, IMqttClient? client, ILogger? logger, int nodeCap = DefaultNodeCap, TimeSpan birthWindow = default)
    {
        Mode = mode;
+        BirthWindow = birthWindow;
        _client = client;
        _logger = logger;
        _nodeCap = nodeCap;
@@ -211,6 +229,59 @@ internal sealed class MqttBrowseSession : IRebirthCapableBrowseSession
    /// </summary>
    internal int PublishCountForTest => Volatile.Read(ref _publishCount);

+    /// <summary>The Sparkplug birth-observation window this session was opened with (R06:M-4).</summary>
+    internal TimeSpan BirthWindow { get; }
+
+    /// <summary>How long a rebirth request waits for its births: the window, capped at <see cref="MaxRebirthWait"/>.</summary>
+    internal TimeSpan RebirthWait => BirthWindow < MaxRebirthWait ? BirthWindow : MaxRebirthWait;
+
+    /// <summary>How many NBIRTH/DBIRTH messages this session has observed — the settle loop's signal.</summary>
+    internal long BirthCount => Interlocked.Read(ref _birthCount);
+
+    /// <summary>
+    ///     Waits until birth traffic has gone quiet for one <paramref name="quiet"/> interval, bounded by
+    ///     <paramref name="window"/> — the <c>UntilStable</c> cadence of the birth-observation window.
+    /// </summary>
+    /// <param name="birthCount">Reads the running birth count.</param>
+    /// <param name="baseline">The count before the wait began.</param>
+    /// <param name="awaitFirstBirth">
+    ///     When true, quiet only counts once at least one birth has arrived past <paramref name="baseline"/>
+    ///     — the shape a rebirth request needs, since its answer takes a broker round-trip to arrive.
+    /// </param>
+    /// <param name="quiet">The quiet spell that ends the wait.</param>
+    /// <param name="window">The hard ceiling; non-positive returns at once.</param>
+    /// <param name="cancellationToken">Cancels the wait.</param>
+    /// <returns>A task that completes when the births have settled or the window has elapsed.</returns>
+    internal static async Task SettleBirthsAsync(
+        Func<long> birthCount,
+        long baseline,
+        bool awaitFirstBirth,
+        TimeSpan quiet,
+        TimeSpan window,
+        CancellationToken cancellationToken)
+    {
+        if (window <= TimeSpan.Zero) return;
+
+        var clock = System.Diagnostics.Stopwatch.StartNew();
+        var last = baseline;
+        var sawBirth = !awaitFirstBirth;
+        while (clock.Elapsed < window)
+        {
+            var step = window - clock.Elapsed;
+            await Task.Delay(step < quiet ? step : quiet, cancellationToken).ConfigureAwait(false);
+
+            var now = birthCount();
+            if (now != last)
+            {
+                last = now;
+                sawBirth = true;
+                continue;
+            }
+
+            if (sawBirth) return;
+        }
+    }
+
    /// <summary>The topics this session published, in order — the discriminating view of the above.</summary>
    internal IReadOnlyList<string> PublishedTopicsForTest => [.. _publishedTopics];

@@ -380,16 +451,25 @@ internal sealed class MqttBrowseSession : IRebirthCapableBrowseSession
        var mapped = metric.DataType?.ToDriverDataType();
        var sparkplugName = metric.DataType?.ToString() ?? nameof(SparkplugDataType.Unknown);

+        var isArray = metric.DataType?.IsSparkplugArray() ?? false;
+
        var descriptor = new StringBuilder(metric.BirthType.ToString()).Append(" · ").Append(sparkplugName);
        if (metric.Alias is { } alias) descriptor.Append(" · alias ").Append(alias);
        if (mapped is null) descriptor.Append(" · unsupported in v1 — not bindable");
+        else if (isArray) descriptor.Append(" · array metrics are not read in v1 — not bindable");
+
+        // Unbindable = the ingestor refuses it: an unmapped type, or ANY array variant (SparkplugIngestor
+        // gates on the array bit and never feeds the tag). Such a leaf states NO address, so the
+        // browse-commit refuses it at commit instead of writing a tag that sits at
+        // BadWaitingForInitialData forever (R06:M-5). Labelling it alone was not enough — it still bound.
+        var bindable = mapped is not null && !isArray;

        return new AttributeInfo(
            metric.Name,
            mapped?.ToString() ?? sparkplugName,
-            metric.DataType?.IsSparkplugArray() ?? false,
+            isArray,
            descriptor.ToString(),
-            AddressFields: BuildMetricAddressFields(metric.Name, scope));
+            AddressFields: bindable ? BuildMetricAddressFields(metric.Name, scope) : null);
    }

    /// <summary>
@@ -557,6 +637,8 @@ internal sealed class MqttBrowseSession : IRebirthCapableBrowseSession
        if (!SparkplugTopic.TryParse(topic, out var parsed)) return;
        if (parsed.Type is not (SparkplugMessageType.NBIRTH or SparkplugMessageType.DBIRTH)) return;

+        Interlocked.Increment(ref _birthCount);
+
        // The bound has to be on the whole message: unlike a plain payload, a birth must be parsed
        // entire to yield its metric list, and the parse runs on the shared dispatcher thread.
        if (payload.Length > MaxBirthPayloadBytes)
@@ -898,6 +980,7 @@ internal sealed class MqttBrowseSession : IRebirthCapableBrowseSession
        ArgumentException.ThrowIfNullOrWhiteSpace(scope);

        var targets = ResolveRebirthTargets(scope);
+        var baseline = BirthCount;

        foreach (var (groupId, edgeNodeId) in targets)
        {
@@ -908,6 +991,20 @@ internal sealed class MqttBrowseSession : IRebirthCapableBrowseSession
                .ConfigureAwait(false);
        }

+        // The birth-observation window (R06:M-4): wait — bounded — for the births just asked for to arrive
+        // and settle, so the tree the picker re-renders after this call already carries them. A courtesy,
+        // never a failure: the NCMDs are out, so a caller deadline here still reports the publish.
+        try
+        {
+            await SettleBirthsAsync(
+                    () => BirthCount, baseline, awaitFirstBirth: true, RebirthQuietInterval, RebirthWait, cancellationToken)
+                .ConfigureAwait(false);
+        }
+        catch (OperationCanceledException)
+        {
+            // Published; the caller simply stopped waiting for the answer.
+        }
+
        Touch();
        return targets.Count;
    }
@@ -39,6 +39,15 @@ public sealed class MqttDriverBrowser : IDriverBrowser
    /// <summary>Ceiling on the open budget — the picker must never hang on an unreachable broker.</summary>
    internal const int MaxOpenBudgetSeconds = 30;

+    /// <summary>Ceiling on the Sparkplug birth-observation window — an authored hour must not park a picker.</summary>
+    internal const int MaxBirthWindowSeconds = 120;
+
+    /// <summary>
+    ///     How long the open waits for a quiet spell in birth traffic before handing the session back. An
+    ///     idle plant (births are never retained) costs exactly this, once.
+    /// </summary>
+    internal static readonly TimeSpan BirthQuietInterval = TimeSpan.FromSeconds(1);
+
    /// <summary>Marks the transient browse identity in the broker's client-id/session logs.</summary>
    internal const string BrowseClientIdPrefix = "-browse-";

@@ -77,7 +86,8 @@ public sealed class MqttDriverBrowser : IDriverBrowser
        openCts.CancelAfter(OpenBudget(opts));

        var client = new MqttClientFactory().CreateMqttClient();
-        var session = new MqttBrowseSession(opts.Mode, client, _logger);
+        var birthWindow = opts.Mode == MqttMode.SparkplugB ? BirthWindow(opts) : TimeSpan.Zero;
+        var session = new MqttBrowseSession(opts.Mode, client, _logger, birthWindow: birthWindow);
        try
        {
            // Runs on MQTTnet's dispatcher: record and return, nothing else.
@@ -100,6 +110,29 @@ public sealed class MqttDriverBrowser : IDriverBrowser
                .Build();
            await client.SubscribeAsync(subscribeOptions, openCts.Token).ConfigureAwait(false);

+            if (opts.Mode == MqttMode.SparkplugB)
+            {
+                // The birth-observation window (R06:M-4): births already in flight — an edge node mid-rebirth,
+                // a primary-host flap — are collected until the traffic goes quiet, bounded by the window, so
+                // the first RootAsync is not a snapshot taken in the middle of a burst. Passive: nothing is
+                // published to provoke a birth. An idle plant costs one quiet interval.
+                try
+                {
+                    await MqttBrowseSession.SettleBirthsAsync(
+                            () => session.BirthCount,
+                            baseline: session.BirthCount,
+                            awaitFirstBirth: false,
+                            BirthQuietInterval,
+                            birthWindow,
+                            openCts.Token)
+                        .ConfigureAwait(false);
+                }
+                catch (OperationCanceledException) when (!cancellationToken.IsCancellationRequested)
+                {
+                    // The open budget ran out mid-settle: what has been observed is still a usable session.
+                }
+            }
+
            _logger.LogInformation(
                "AdminUI MQTT browse session opened against {Host}:{Port} in {Mode} mode observing "
                + "'{Filter}' (read-only).",
@@ -179,12 +212,30 @@ public sealed class MqttDriverBrowser : IDriverBrowser
        options with { CleanSession = true };

    /// <summary>
-    ///     Whole-open bound (connect + subscribe), clamped to
-    ///     <see cref="MinOpenBudgetSeconds"/>–<see cref="MaxOpenBudgetSeconds"/> around the config's
-    ///     own connect deadline.
+    ///     Whole-open bound: connect + subscribe, clamped to
+    ///     <see cref="MinOpenBudgetSeconds"/>–<see cref="MaxOpenBudgetSeconds"/> around the config's own
+    ///     connect deadline — plus, in Sparkplug mode, the <see cref="BirthWindow"/> the open may spend
+    ///     collecting births.
    /// </summary>
    /// <param name="options">The browse configuration.</param>
-    /// <returns>The clamped open budget.</returns>
-    internal static TimeSpan OpenBudget(MqttDriverOptions options) =>
-        TimeSpan.FromSeconds(Math.Clamp(options.ConnectTimeoutSeconds, MinOpenBudgetSeconds, MaxOpenBudgetSeconds));
+    /// <returns>The open budget.</returns>
+    internal static TimeSpan OpenBudget(MqttDriverOptions options)
+    {
+        var connect = TimeSpan.FromSeconds(
+            Math.Clamp(options.ConnectTimeoutSeconds, MinOpenBudgetSeconds, MaxOpenBudgetSeconds));
+        return options.Mode == MqttMode.SparkplugB ? connect + BirthWindow(options) : connect;
+    }
+
+    /// <summary>
+    ///     The authored <c>sparkplug.birthObservationWindowSeconds</c>, clamped to 1–<see cref="MaxBirthWindowSeconds"/>
+    ///     s: how long the browse surface collects NBIRTH/DBIRTH traffic before calling the observed metric set
+    ///     stable (on open, and after an operator rebirth request).
+    /// </summary>
+    /// <param name="options">The browse configuration.</param>
+    /// <returns>The clamped window.</returns>
+    internal static TimeSpan BirthWindow(MqttDriverOptions options) =>
+        TimeSpan.FromSeconds(Math.Clamp(
+            options.Sparkplug?.BirthObservationWindowSeconds ?? new MqttSparkplugOptions().BirthObservationWindowSeconds,
+            1,
+            MaxBirthWindowSeconds));
 }
@@ -45,6 +45,30 @@ public sealed class LastValueCache
        _values[rawPath] = snapshot;
    }

+    /// <summary>How many RawPaths currently hold an entry. Diagnostics and the bounded-growth tests.</summary>
+    internal int Count => _values.Count;
+
+    /// <summary>
+    ///     Drops every entry whose RawPath <paramref name="keep"/> rejects — called by each ingest path's
+    ///     <c>Register</c> with "is this still an authored tag", so the cache is bounded by the CURRENT
+    ///     authored set rather than by the union of every RawPath (and every non-authored reference ever
+    ///     subscribed) across the driver's lifetime (R06:M-2).
+    /// </summary>
+    /// <param name="keep">Returns <see langword="true"/> for a RawPath whose entry must survive.</param>
+    /// <returns>How many entries were dropped.</returns>
+    public int RetainOnly(Func<string, bool> keep)
+    {
+        ArgumentNullException.ThrowIfNull(keep);
+        var dropped = 0;
+        foreach (var rawPath in _values.Keys)
+        {
+            if (!keep(rawPath) && _values.TryRemove(rawPath, out _))
+                dropped++;
+        }
+
+        return dropped;
+    }
+
    /// <summary>
    ///     Read the last observed value for <paramref name="rawPath"/>. Never throws: a
    ///     <c>null</c>/empty <paramref name="rawPath"/> or a RawPath never observed both return a
@@ -104,6 +104,12 @@ public sealed class MqttDriver
    /// </summary>
    private const string DiscoveryFolderName = "Mqtt";

+    /// <summary>
+    ///     Ceiling on PUBLISHes one write batch keeps in flight (R06:M-8). Bounded so a large batch cannot
+    ///     flood a broker's inflight window; different topics share it, one topic's writes stay sequential.
+    /// </summary>
+    internal const int MaxConcurrentPublishes = 8;
+
    /// <summary>How often the host-connectivity poll samples <see cref="MqttConnection.State"/>.</summary>
    private static readonly TimeSpan HostProbeInterval = TimeSpan.FromSeconds(1);

@@ -208,6 +214,18 @@ public sealed class MqttDriver
    private SparkplugPrimaryHost? _primaryHost;

    private DriverHealth _health = new(DriverState.Unknown, null, null);
+
+    /// <summary>UTC ticks of the last successful write PUBLISH; 0 = none. Answer evidence for health.</summary>
+    private long _lastPublishUtcTicks;
+
+    /// <summary>Guards the generation bump against the generation-checked health write.</summary>
+    private readonly object _healthLock = new();
+
+    /// <summary>
+    ///     Bumped by every lifecycle operation (initialize inside the gate; shutdown and dispose before
+    ///     waiting for it). The stamp that keeps a superseded operation from publishing state.
+    /// </summary>
+    private long _lifecycleGeneration;
    private HostState _hostState = HostState.Unknown;
    private DateTime _hostStateChangedUtc = DateTime.UtcNow;
    private int _disposed;
@@ -289,6 +307,9 @@ public sealed class MqttDriver
    /// </summary>
    internal Func<CancellationToken, Task>? BeforeConnectHookForTests { get; set; }

+    /// <summary>Test seam: observes every <see cref="MqttConnection"/> an initialize builds. Null in production.</summary>
+    internal Action<MqttConnection>? ConnectionCreatedForTests { get; set; }
+
    // ---- IDriver: lifecycle ----

    /// <inheritdoc />
@@ -387,6 +408,11 @@ public sealed class MqttDriver
        // watchdog's reconnect) is measured against, reporting a driver that was delivering a moment ago
        // as one that has never delivered.
        var lastMessage = GetHealth().LastSuccessfulRead;
+
+        // Taken BEFORE the gate wait: a wedged initialize holding the gate is superseded by this call, so
+        // when it finally completes it disposes the session it built instead of publishing it behind the
+        // ungated teardown below (R06:M-10), and its late health write is refused.
+        var generation = BeginLifecycleOperation();
        if (await _lifecycleGate.WaitAsync(TimeSpan.FromSeconds(_options.ConnectTimeoutSeconds), cancellationToken)
                .ConfigureAwait(false))
        {
@@ -408,8 +434,10 @@ public sealed class MqttDriver
            await TeardownAsync().ConfigureAwait(false);
        }

-        WriteHealth(new DriverHealth(DriverState.Unknown, lastMessage, null));
-        TransitionHost(HostState.Unknown);
+        if (WriteHealthIfCurrent(generation, new DriverHealth(DriverState.Unknown, lastMessage, null)))
+        {
+            TransitionHost(HostState.Unknown);
+        }
    }

    /// <inheritdoc />
@@ -427,7 +455,7 @@ public sealed class MqttDriver
            return stored;
        }

-        var lastMessage = connection.LastMessageUtc ?? stored.LastSuccessfulRead;
+        var lastMessage = Latest(connection.LastMessageUtc ?? stored.LastSuccessfulRead, LastPublishUtc);
        return connection.State switch
        {
            MqttConnectionState.Connected => new DriverHealth(DriverState.Healthy, lastMessage, stored.LastError),
@@ -689,9 +717,12 @@ public sealed class MqttDriver
    {
        ArgumentNullException.ThrowIfNull(writes);

-        var results = new WriteResult[writes.Count];
+        var results = new WriteResult?[writes.Count];
        var connection = _connection;

+        // Pass 1 — everything that needs no broker: resolve, encode, refuse. What survives is grouped by
+        // destination topic in REQUEST order.
+        var byTopic = new Dictionary<string, List<(int Index, MqttEncodedWrite Encoded, string Reference)>>(StringComparer.Ordinal);
        for (var i = 0; i < writes.Count; i++)
        {
            var w = writes[i];
@@ -719,22 +750,72 @@ public sealed class MqttDriver
                continue;
            }

+            if (!byTopic.TryGetValue(encoded.Topic, out var queue))
+            {
+                byTopic[encoded.Topic] = queue = [];
+            }
+
+            queue.Add((i, encoded, w.FullReference));
+        }
+
+        // Pass 2 — publish (R06:M-8). Different topics go out concurrently, at most MaxConcurrentPublishes
+        // in flight, so a stalled broker costs a batch ~one publish deadline instead of one per request.
+        // Writes to the SAME topic stay strictly sequential in request order: the device applies them in
+        // arrival order, and the last one must win.
+        if (byTopic.Count > 0)
+        {
+            using var slots = new SemaphoreSlim(MaxConcurrentPublishes, MaxConcurrentPublishes);
+            await Task.WhenAll(byTopic.Values.Select(queue => PublishQueueAsync(connection!, queue, slots, results, cancellationToken)))
+                .ConfigureAwait(false);
+        }
+
+        // Every slot is filled — a caller cancellation leaves the unattempted ones BadCommunicationError
+        // rather than throwing, so the batch shape holds.
+        var filled = new WriteResult[writes.Count];
+        for (var i = 0; i < filled.Length; i++)
+        {
+            filled[i] = results[i] ?? new WriteResult(StatusBadCommunicationError);
+        }
+
+        return filled;
+    }
+
+    /// <summary>Publishes one topic's writes in request order, each under a shared concurrency slot.</summary>
+    private async Task PublishQueueAsync(
+        MqttConnection connection,
+        List<(int Index, MqttEncodedWrite Encoded, string Reference)> queue,
+        SemaphoreSlim slots,
+        WriteResult?[] results,
+        CancellationToken cancellationToken)
+    {
+        foreach (var (index, encoded, reference) in queue)
+        {
+            try
+            {
+                await slots.WaitAsync(cancellationToken).ConfigureAwait(false);
+            }
+            catch (OperationCanceledException)
+            {
+                return;   // caller-cancelled: the remaining slots are filled by the caller
+            }
+
            try
            {
                await connection
                    .PublishAsync(encoded.Topic, encoded.Payload, encoded.Qos, retain: false, cancellationToken)
                    .ConfigureAwait(false);
-                results[i] = new WriteResult(0u);
+                results[index] = new WriteResult(0u);
+
+                // A PUBACK is the broker answering — evidence the session works, so it feeds
+                // LastSuccessfulRead alongside inbound messages. A completed QoS 0 publish is NOT: it only
+                // means the bytes reached the local socket buffer, and frequent Sparkplug commands would
+                // otherwise keep the watchdog's clock fresh over a half-open session (review minor 2).
+                if (encoded.Qos >= 1) Interlocked.Exchange(ref _lastPublishUtcTicks, DateTime.UtcNow.Ticks);
            }
            catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
            {
-                // Caller-cancelled: fill the remainder rather than throwing, so the batch shape holds.
-                for (var j = i; j < writes.Count; j++)
-                {
-                    results[j] = new WriteResult(StatusBadCommunicationError);
-                }
-
-                return results;
+                results[index] = new WriteResult(StatusBadCommunicationError);
+                return;
            }
            catch (Exception ex)
            {
@@ -742,13 +823,15 @@ public sealed class MqttDriver
                    ex,
                    "MQTT driver '{DriverId}': write to '{Reference}' could not be published on '{Topic}'.",
                    _driverInstanceId,
-                    w.FullReference,
+                    reference,
                    encoded.Topic);
-                results[i] = new WriteResult(StatusBadCommunicationError);
+                results[index] = new WriteResult(StatusBadCommunicationError);
+            }
+            finally
+            {
+                slots.Release();
            }
        }
-
-        return results;
    }

    /// <summary>Maps an encode refusal to the status an OPC UA client sees.</summary>
@@ -911,6 +994,9 @@ public sealed class MqttDriver
            return;
        }

+        // Supersedes any in-flight lifecycle operation, exactly as ShutdownAsync does.
+        BeginLifecycleOperation();
+
        if (await _lifecycleGate.WaitAsync(TimeSpan.FromSeconds(_options.ConnectTimeoutSeconds))
                .ConfigureAwait(false))
        {
@@ -940,7 +1026,12 @@ public sealed class MqttDriver
    /// <summary>The gate-held body of <see cref="InitializeAsync"/>.</summary>
    private async Task InitializeCoreAsync(string driverConfigJson, CancellationToken cancellationToken)
    {
-        WriteHealth(new DriverHealth(DriverState.Initializing, ReadHealth().LastSuccessfulRead, null));
+        // Taken INSIDE the gate (the caller holds it), so a second initialize queued behind this one does
+        // not supersede it; only a ShutdownAsync / DisposeAsync — which take theirs before waiting — can.
+        var generation = BeginLifecycleOperation();
+        WriteHealthIfCurrent(generation, new DriverHealth(DriverState.Initializing, ReadHealth().LastSuccessfulRead, null));
+        MqttConnection? built = null;
+        var published = false;
        try
        {
            // Tear down whatever this driver already holds BEFORE building a new session. Both fields
@@ -965,6 +1056,8 @@ public sealed class MqttDriver
            RegisterAuthoredTags(_options);

            var connection = new MqttConnection(_options, _driverInstanceId, _logger);
+            built = connection;
+            ConnectionCreatedForTests?.Invoke(connection);

            // MUST precede the connect: this wires message delivery AND the reconnect re-subscribe.
            // The handler is passed through unwrapped on purpose — its throw-on-total-failure is what
@@ -992,10 +1085,13 @@ public sealed class MqttDriver
            // disposing what we just built, never leaking it.
            if (Volatile.Read(ref _disposed) != 0)
            {
-                await connection.DisposeAsync().ConfigureAwait(false);
                throw new ObjectDisposedException(nameof(MqttDriver));
            }

+            // The same race against a ShutdownAsync whose bounded gate wait expired: it has already torn
+            // down ungated, so publishing now would leave a live session no later shutdown can see.
+            ThrowIfSuperseded(generation);
+
            // Sparkplug subscribes ONCE, here, rather than on the OPC UA server's first subscribe: the
            // driver must see birth certificates whether or not anything is subscribed yet, because a
            // birth is where every alias and datatype comes from. This also issues the late-join
@@ -1008,28 +1104,47 @@ public sealed class MqttDriver
            // MqttConnection's own remarks describe having already fixed once.
            if (_sparkplug is { } sparkplug)
            {
-                try
-                {
-                    await sparkplug.EstablishAsync(cancellationToken).ConfigureAwait(false);
-                }
-                catch
-                {
-                    await connection.DisposeAsync().ConfigureAwait(false);
-                    throw;
-                }
+                await sparkplug.EstablishAsync(cancellationToken).ConfigureAwait(false);
            }

+            ThrowIfSuperseded(generation);
            _connection = connection;
+            published = true;
+
+            if (WriteHealthIfCurrent(generation, new DriverHealth(DriverState.Healthy, connection.LastMessageUtc, null)))
+            {
+                TransitionHost(HostState.Running);
+            }

-            WriteHealth(new DriverHealth(DriverState.Healthy, connection.LastMessageUtc, null));
-            TransitionHost(HostState.Running);
            StartHostProbe();
            await StartPrimaryHostAsync(cancellationToken).ConfigureAwait(false);
+
+            // Re-checked after publishing: a shutdown whose gate wait expired between the check above and
+            // here captured whatever it found and left these fields for us. Intended consequence (review
+            // minor 8): a perfectly healthy init that is just completing when a ShutdownAsync arrives also
+            // releases itself and throws OperationCanceledException — the queued shutdown would tear it down
+            // anyway, and the actor serialises init/shutdown, so only an abandoned init can meet this. We still hold the gate, so no
+            // newer initialize can have published anything — everything in them is ours to release.
+            if (!IsCurrentLifecycle(generation))
+            {
+                await TeardownAsync().ConfigureAwait(false);
+                ThrowIfSuperseded(generation);
+            }
        }
        catch (Exception ex)
        {
-            WriteHealth(new DriverHealth(DriverState.Faulted, ReadHealth().LastSuccessfulRead, ex.Message));
-            TransitionHost(HostState.Faulted);
+            // R06:M-3: a connection built but never published is disposed here — a refused connect, a
+            // failed Sparkplug establish, a supersede. The published one belongs to TeardownAsync.
+            if (!published && built is not null)
+            {
+                await built.DisposeAsync().ConfigureAwait(false);
+            }
+
+            if (WriteHealthIfCurrent(generation, new DriverHealth(DriverState.Faulted, ReadHealth().LastSuccessfulRead, ex.Message)))
+            {
+                TransitionHost(HostState.Faulted);
+            }
+
            throw;
        }
    }
@@ -1380,24 +1495,28 @@ public sealed class MqttDriver
    /// <summary>Shared teardown for <see cref="ShutdownAsync"/>, <see cref="DisposeAsync"/> and the session rebuild.</summary>
    private async Task TeardownAsync()
    {
+        // Every field is CAPTURED before anything is disposed. A shutdown that timed out on the gate runs
+        // this ungated; capturing up front means it only ever releases what existed when it started, and
+        // never reaches into fields a later initialize publishes while the slow disposals below run.
+        var primaryHost = Interlocked.Exchange(ref _primaryHost, null);
+        var probe = Interlocked.Exchange(ref _hostProbeCts, null);
+        var connection = Interlocked.Exchange(ref _connection, null);
+
        // Stand the host claim down FIRST, while the broker is still reachable and before the ingest
        // session goes. Its explicit retained OFFLINE is what makes the transition immediate for edge
        // nodes; leaving it to the Will costs them up to 1.5 keep-alive periods of believing a host
        // that has already stopped is still online.
-        var primaryHost = Interlocked.Exchange(ref _primaryHost, null);
        if (primaryHost is not null)
        {
            await primaryHost.DisposeAsync().ConfigureAwait(false);
        }

-        var probe = Interlocked.Exchange(ref _hostProbeCts, null);
        if (probe is not null)
        {
            await probe.CancelAsync().ConfigureAwait(false);
            probe.Dispose();
        }

-        var connection = Interlocked.Exchange(ref _connection, null);
        if (connection is not null)
        {
            await connection.DisposeAsync().ConfigureAwait(false);
@@ -1476,9 +1595,66 @@ public sealed class MqttDriver
        OnHostStatusChanged?.Invoke(this, new HostStatusChangedEventArgs(HostName, previous, next));
    }

+    /// <summary>The last successful write publish, or null.</summary>
+    private DateTime? LastPublishUtc
+    {
+        get
+        {
+            var ticks = Interlocked.Read(ref _lastPublishUtcTicks);
+            return ticks == 0 ? null : new DateTime(ticks, DateTimeKind.Utc);
+        }
+    }
+
+    /// <summary>The later of two optional instants.</summary>
+    private static DateTime? Latest(DateTime? a, DateTime? b)
+        => a is null ? b : b is null ? a : (a > b ? a : b);
+
    /// <summary>Barrier-protected read of the multi-threaded health field.</summary>
    private DriverHealth ReadHealth() => Volatile.Read(ref _health);

-    /// <summary>Barrier-protected publish of a new health snapshot.</summary>
-    private void WriteHealth(DriverHealth value) => Volatile.Write(ref _health, value);
+    /// <summary>
+    ///     Starts a lifecycle operation and returns its generation. Every later operation supersedes it:
+    ///     its health / host-state writes are refused and an initialize stops before publishing a session.
+    /// </summary>
+    private long BeginLifecycleOperation()
+    {
+        lock (_healthLock)
+        {
+            return ++_lifecycleGeneration;
+        }
+    }
+
+    /// <summary>Whether <paramref name="generation"/> is still the newest lifecycle operation.</summary>
+    private bool IsCurrentLifecycle(long generation) => Interlocked.Read(ref _lifecycleGeneration) == generation;
+
+    /// <summary>Throws when a newer lifecycle operation has superseded <paramref name="generation"/>.</summary>
+    private void ThrowIfSuperseded(long generation)
+    {
+        if (!IsCurrentLifecycle(generation))
+        {
+            throw new OperationCanceledException(
+                $"MQTT driver '{_driverInstanceId}': this initialize was superseded by a later shutdown/dispose; "
+                + "the session it built has been released.");
+        }
+    }
+
+    /// <summary>
+    ///     Publishes a health snapshot only while <paramref name="generation"/> is the newest lifecycle
+    ///     operation — the check and the write are atomic against <see cref="BeginLifecycleOperation"/>, so a
+    ///     superseded initialize or shutdown can never overwrite a newer one's state.
+    /// </summary>
+    /// <returns><see langword="true"/> when the write was applied.</returns>
+    private bool WriteHealthIfCurrent(long generation, DriverHealth value)
+    {
+        lock (_healthLock)
+        {
+            if (_lifecycleGeneration != generation)
+            {
+                return false;
+            }
+
+            Volatile.Write(ref _health, value);
+            return true;
+        }
+    }
 }
@@ -48,7 +48,8 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Mqtt;
 ///         accepted by the parser (warned at deploy, see <c>MqttTagDefinitionFactory.Inspect</c>), so
 ///         matching uses MQTTnet's own <see cref="MqttTopicFilterComparer"/> rather than string
 ///         equality — the same comparer a broker applies. Concrete topics stay a single dictionary
-///         lookup; the linear wildcard scan runs only when a wildcard tag actually exists.
+///         lookup; wildcard filters live in a level trie (<c>TopicFilterTrie</c>) whose candidates the comparer
+///         confirms, so a thousand wildcard tags cost a walk over the topic's levels, not a thousand compares.
 ///     </para>
 ///     <para>
 ///         <b>Sparkplug seam.</b> P1 ingests plain topics only. Sparkplug B decodes a
@@ -74,6 +75,13 @@ public sealed class MqttSubscriptionManager
    /// </summary>
    public const int DefaultQos = 1;

+    /// <summary>
+    ///     Throw-on-invalid UTF-8, shared (R06:M-7): it is stateless and thread-safe, and allocating one per
+    ///     Raw/Scalar delivery was per-message garbage on the dispatcher thread. Same choice
+    ///     <c>MqttBrowseSession</c> makes.
+    /// </summary>
+    private static readonly UTF8Encoding Utf8Strict = new(encoderShouldEmitUTF8Identifier: false, throwOnInvalidBytes: true);
+
    // OPC UA status codes (values verified against Opc.Ua.StatusCodes, not recalled).
    private const uint StatusGood = 0x00000000u;

@@ -113,6 +121,14 @@ public sealed class MqttSubscriptionManager
    /// <summary>Topics already SUBSCRIBEd on the live session — the dedupe set and the re-subscribe set.</summary>
    private readonly ConcurrentDictionary<string, byte> _subscribedTopics = new(StringComparer.Ordinal);

+    /// <summary>
+    ///     Topics a subscribe asked for whose SUBSCRIBE failed (refused, or no verdict at all). Retried by
+    ///     every later <see cref="SubscribeAsync"/> and by <see cref="OnReconnectedAsync"/>; moved to
+    ///     <see cref="_subscribedTopics"/> when granted. Without it a failed topic left every retry set and
+    ///     stayed dark behind a Healthy connection until a redeploy.
+    /// </summary>
+    private readonly ConcurrentDictionary<string, byte> _pendingTopics = new(StringComparer.Ordinal);
+
    /// <summary>RawPaths whose extraction failure has already been logged loudly once.</summary>
    private readonly ConcurrentDictionary<string, byte> _warnedRefs = new(StringComparer.Ordinal);

@@ -212,8 +228,8 @@ public sealed class MqttSubscriptionManager
    ///         The manager does not own the connection's lifetime and never detaches — the driver disposes
    ///         both together. Call once per connection, and <b>before</b> the first
    ///         <see cref="SubscribeAsync"/>: a subscribe issued with no transport attached records its
-    ///         intent (and warns) but sends nothing to a broker, and would only be established if the
-    ///         connection later dropped and recovered.
+    ///         topics as <i>pending</i> (and warns) but sends nothing to a broker; the next subscribe or
+    ///         reconnect on an attached session retries them.
    ///     </para>
    ///     <para>
    ///         <b>Binding to a session forgets the previous session's established filters</b> — the same
@@ -317,6 +333,11 @@ public sealed class MqttSubscriptionManager
        _authored = table;
        _warnedRefs.Clear();

+        // Bound the shared last-value cache by the CURRENT authored set (R06:M-2): a dropped tag's value
+        // and every non-authored reference's BadNodeIdUnknown marker would otherwise live forever. A
+        // still-authored tag keeps its value, so a redeploy never blanks what has been observed.
+        Values.RetainOnly(table.ByRawPath.ContainsKey);
+
        // Drop state belonging to tags this deploy removed. Without this, a topic whose last tag was
        // deleted stays in _subscribedTopics and is dutifully re-SUBSCRIBEd on every future reconnect,
        // forever — and its RawPaths keep a handle mapping that can never fire again.
@@ -328,6 +349,14 @@ public sealed class MqttSubscriptionManager
            }
        }

+        foreach (var topic in _pendingTopics.Keys)
+        {
+            if (!table.ByFilter.ContainsKey(topic))
+            {
+                _pendingTopics.TryRemove(topic, out _);
+            }
+        }
+
        foreach (var rawPath in _handleByRawPath.Keys)
        {
            if (!table.ByRawPath.ContainsKey(rawPath))
@@ -356,12 +385,13 @@ public sealed class MqttSubscriptionManager
    ///         opening SUBSCRIBE itself; <see cref="OnReconnectedAsync"/> only re-establishes it later.
    ///     </para>
    ///     <para>
-    ///         <b>Never throws, never hangs.</b> A reference that is not an authored tag is recorded as
-    ///         <c>BadNodeIdUnknown</c>; a SUBACK rejection, transport failure or subscribe deadline
-    ///         degrades exactly the affected references to <c>BadCommunicationError</c>. Either way a
-    ///         handle is returned — the OPC UA server's subscribe call must not fail because one topic
-    ///         is ACL-denied. Recovery for a transient failure comes from the reconnect path;
-    ///         a persistent broker-side refusal is visible as a Bad status on the affected nodes.
+    ///         <b>Never hangs; throws only when the broker gave no verdict.</b> A reference that is not an
+    ///         authored tag is recorded as <c>BadNodeIdUnknown</c>. A SUBACK rejection degrades exactly the
+    ///         affected references to <c>BadCommunicationError</c> and still returns a handle — the OPC UA
+    ///         server's subscribe must not fail because one topic is ACL-denied. A transport failure or
+    ///         subscribe deadline degrades the same way and then <b>throws</b>, so the host holds no handle
+    ///         and its reconcile re-subscribes. Every failed topic also joins a pending set that the next
+    ///         subscribe and every reconnect retry.
    ///     </para>
    /// </remarks>
    /// <param name="fullReferences">The RawPath references to subscribe.</param>
@@ -414,12 +444,56 @@ public sealed class MqttSubscriptionManager

        // One SUBSCRIBE per distinct topic, and only for topics not already live: re-SUBSCRIBEing an
        // established filter is legal but pointless, and it re-triggers the retained seed.
-        var pending = defs.Where(d => !_subscribedTopics.ContainsKey(d.Topic)).ToList();
-        await EstablishAsync(BuildFilters(pending, _defaultQos), cancellationToken).ConfigureAwait(false);
+        // Topics an EARLIER subscribe failed to establish ride along: a redeploy's bulk re-subscribe is then a
+        // retry of a refusal the broker may since have lifted, instead of a no-op that leaves them dark.
+        var authored = _authored;
+        var pending = defs.Where(d => !_subscribedTopics.ContainsKey(d.Topic))
+            .Concat(PendingDefinitions(authored))
+            .ToList();
+        var outcome = await EstablishAsync(BuildFilters(pending, _defaultQos), cancellationToken).ConfigureAwait(false);

+        if (outcome.TransportFailure is { } failure)
+        {
+            // The refs are already Bad and pending either way. But a cancel of the CALLER's token (a pipeline
+            // timeout, host shutdown) is a cancellation, not a broker fault: surfacing it as
+            // InvalidOperationException made the resilience breaker count it as a failure (review minor 3).
+            var callerCancelled = cancellationToken.IsCancellationRequested;
+            // No verdict at all (transport throw / SUBSCRIBE deadline): THROW, so the caller holds no handle
+            // and DriverInstanceActor's health-tick reconcile re-subscribes. Returning a handle here was the
+            // silent-death case — the actor thought the subscription live and never retried. The refs already
+            // carry BadCommunicationError (raised under this handle above), so the throw costs no visibility.
+            _refsByHandle.TryRemove(handle, out _);
+            foreach (var def in defs)
+            {
+                _handleByRawPath.TryRemove(new KeyValuePair<string, ISubscriptionHandle>(def.Name, handle));
+            }
+
+            if (callerCancelled)
+            {
+                throw new OperationCanceledException(
+                    $"MQTT driver '{_driverId}': SUBSCRIBE for {pending.Count} tag(s) was cancelled by the caller; "
+                    + "the topics stay pending and will be retried.",
+                    failure,
+                    cancellationToken);
+            }
+
+            throw new InvalidOperationException(
+                $"MQTT driver '{_driverId}': SUBSCRIBE for {pending.Count} tag(s) got no broker verdict "
+                + $"({failure.GetType().Name}); the subscription will be retried.",
+                failure);
+        }
+
+        // A SUBACK refusal (an ACL denial, say) does NOT throw: the broker answered, the refused topics are
+        // Bad + pending, and failing the whole subscribe would take every other topic in it dark too.
        return handle;
    }

+    /// <summary>The authored definitions behind every still-authored pending topic.</summary>
+    private IEnumerable<MqttTagDefinition> PendingDefinitions(AuthoredTable authored)
+        => _pendingTopics.Keys
+            .Select(topic => authored.ByFilter.TryGetValue(topic, out var defs) ? defs : [])
+            .SelectMany(defs => defs);
+
    /// <summary>
    ///     Stops attributing notifications to <paramref name="handle"/>. References another live
    ///     subscription also covers keep publishing.
@@ -498,8 +572,13 @@ public sealed class MqttSubscriptionManager
            .SelectMany(defs => defs)
            .ToList();

-        var filters = BuildFilters(live, _defaultQos);
-        if (filters.Count == 0)
+        // Pending topics (a failed earlier SUBSCRIBE) are retried here too — a reconnect re-subscribing
+        // only the granted set is how a failed topic stayed dark forever. They do NOT count toward the
+        // total-failure verdict below: re-refusing a topic that was never live loses nothing, and throwing
+        // for it would turn one ACL-denied topic into a reconnect loop for the whole driver.
+        var pendingDefs = PendingDefinitions(authored).ToList();
+        var filters = BuildFilters(live.Concat(pendingDefs), _defaultQos);
+        if (live.Count == 0 && pendingDefs.Count == 0)
        {
            // Silence here is how the wildcard defect hid: no exception, no log, no SUBSCRIBE. Live
            // topics resolving to zero filters re-establishes nothing, which is the total-failure case
@@ -519,13 +598,17 @@ public sealed class MqttSubscriptionManager
            return;
        }

-        var granted = await EstablishAsync(filters, cancellationToken).ConfigureAwait(false);
-        if (granted == 0)
+        var outcome = await EstablishAsync(filters, cancellationToken).ConfigureAwait(false);
+        var liveTopics = live.Select(d => d.Topic).Distinct(StringComparer.Ordinal).ToList();
+        var liveLost = outcome.TransportFailure is not null
+                       || (subscribed.Count > 0 && (liveTopics.Count == 0 || !liveTopics.Any(outcome.Granted.Contains)));
+        if (liveLost)
        {
            throw new InvalidOperationException(
                $"MQTT driver '{_driverId}': no subscription could be re-established after reconnect "
                + $"({filters.Count} filter(s) requested); tearing the session down rather than serving a "
-                + "connection that receives nothing.");
+                + "connection that receives nothing.",
+                outcome.TransportFailure);
        }
    }

@@ -582,13 +665,14 @@ public sealed class MqttSubscriptionManager
            }

            // A published topic name may not itself contain a wildcard, so a wildcard-authored
-            // definition can never also be an exact-index hit: no tag is delivered twice.
-            foreach (var def in authored.Wildcards)
+            // definition can never also be an exact-index hit: no tag is delivered twice. The trie walks
+            // the topic's levels (R06:M-6 — this used to be one comparer call per wildcard tag, per
+            // message, on the shared dispatcher thread) and every candidate it yields is confirmed by
+            // MQTTnet's own comparer inside the visitor, so the semantics are the broker's.
+            if (authored.WildcardTrie.Count > 0)
            {
-                if (MqttTopicFilterComparer.Compare(topic, def.Topic) == MqttTopicFilterCompareResult.IsMatch)
-                {
-                    Deliver(def, payload, retained, now, oversized, ref json);
-                }
+                var visitor = new WildcardDelivery(this, topic, payload, retained, now, oversized, ref json);
+                authored.WildcardTrie.Match(topic, ref visitor);
            }
        }
        finally
@@ -633,35 +717,35 @@ public sealed class MqttSubscriptionManager
    /// </summary>
    /// <param name="filters">The filters to establish; an empty list is a no-op.</param>
    /// <param name="cancellationToken">Cancellation for the round-trip.</param>
-    /// <returns>How many filters the broker granted.</returns>
-    private async Task<int> EstablishAsync(
+    /// <returns>The granted topics, plus the transport failure when the broker gave no verdict at all.</returns>
+    private async Task<EstablishOutcome> EstablishAsync(
        IReadOnlyList<MqttTopicSubscription> filters,
        CancellationToken cancellationToken)
    {
        if (filters.Count == 0)
        {
-            return 0;
+            return EstablishOutcome.Nothing;
        }

        var transport = _transport;
        if (transport is null)
        {
-            // No transport: the intent is recorded so the reconnect path establishes it, but NOTHING
-            // reaches a broker now. Loud, because outside tests this means the composition order is
-            // wrong — AttachTo must run before the OPC UA server's first subscribe, or these topics
-            // stay unestablished until the connection happens to drop and recover.
+            // No transport: NOTHING reaches a broker, so nothing is recorded as subscribed — recording it
+            // was a silent "subscribed, receives nothing" if the AttachTo-before-subscribe ordering ever
+            // changed. The topics wait in the pending set, which the next subscribe and every reconnect
+            // retry. Loud, because outside tests this means the composition order is wrong.
            foreach (var filter in filters)
            {
-                _subscribedTopics[filter.Topic] = 0;
+                _pendingTopics[filter.Topic] = 0;
            }

            _logger?.LogWarning(
-                "MQTT driver '{DriverId}': {FilterCount} subscription(s) recorded with no connection attached; "
-                + "nothing was sent to a broker. Call AttachTo before subscribing.",
+                "MQTT driver '{DriverId}': {FilterCount} subscription(s) requested with no connection attached; "
+                + "nothing was sent to a broker and they stay pending. Call AttachTo before subscribing.",
                _driverId,
                filters.Count);

-            return filters.Count;
+            return EstablishOutcome.Nothing;
        }

        IReadOnlyList<MqttSubscribeOutcome> outcomes;
@@ -681,16 +765,17 @@ public sealed class MqttSubscriptionManager
                DegradeTopic(filter.Topic, ex.GetType().Name);
            }

-            return 0;
+            return new EstablishOutcome(new HashSet<string>(StringComparer.Ordinal), ex);
        }

-        var granted = 0;
+        var granted = new HashSet<string>(StringComparer.Ordinal);
        foreach (var outcome in outcomes)
        {
            if (outcome.Granted)
            {
                _subscribedTopics[outcome.Topic] = 0;
-                granted++;
+                _pendingTopics.TryRemove(outcome.Topic, out _);
+                granted.Add(outcome.Topic);
            }
            else
            {
@@ -703,7 +788,16 @@ public sealed class MqttSubscriptionManager
            }
        }

-        return granted;
+        return new EstablishOutcome(granted, null);
+    }
+
+    /// <summary>One SUBSCRIBE round-trip's verdict.</summary>
+    /// <param name="Granted">The filters the broker granted.</param>
+    /// <param name="TransportFailure">Set when the call produced no verdict at all (throw / deadline).</param>
+    private sealed record EstablishOutcome(IReadOnlySet<string> Granted, Exception? TransportFailure)
+    {
+        public static readonly EstablishOutcome Nothing =
+            new(new HashSet<string>(StringComparer.Ordinal), null);
    }

    /// <summary>Marks every authored reference on <paramref name="topic"/> as unreachable.</summary>
@@ -722,6 +816,7 @@ public sealed class MqttSubscriptionManager

        if (!_authored.ByFilter.TryGetValue(topic, out var defs))
        {
+            _pendingTopics.TryRemove(topic, out _);
            _logger?.LogWarning(
                "MQTT driver '{DriverId}': cannot degrade tags for unestablished filter '{Topic}' ({Reason}) — "
                + "no authored tag resolves to it.",
@@ -731,6 +826,9 @@ public sealed class MqttSubscriptionManager
            return;
        }

+        // Still authored, so it must be retried — see _pendingTopics.
+        _pendingTopics[topic] = 0;
+
        var now = DateTime.UtcNow;
        var snapshot = new DataValueSnapshot(null, StatusBadCommunicationError, null, now);
        foreach (var def in defs)
@@ -1371,8 +1469,7 @@ public sealed class MqttSubscriptionManager
    {
        try
        {
-            text = new UTF8Encoding(encoderShouldEmitUTF8Identifier: false, throwOnInvalidBytes: true)
-                .GetString(payload);
+            text = Utf8Strict.GetString(payload);
            return true;
        }
        catch (DecoderFallbackException)
@@ -1400,6 +1497,47 @@ public sealed class MqttSubscriptionManager
        return $"mqtt:{_mode}:{id}:[{named}{overflow}]";
    }

+    /// <summary>
+    ///     Delivers each wildcard-trie candidate whose filter the MQTTnet comparer confirms. A <c>ref struct</c>
+    ///     so the payload span and the fan-out's shared JSON parse ride along without a closure or a list.
+    /// </summary>
+    private ref struct WildcardDelivery : ITopicFilterVisitor<MqttTagDefinition>
+    {
+        private readonly MqttSubscriptionManager _manager;
+        private readonly string _topic;
+        private readonly ReadOnlySpan<byte> _payload;
+        private readonly bool _retained;
+        private readonly DateTime _now;
+        private readonly bool _oversized;
+        private ref PayloadJson _json;
+
+        public WildcardDelivery(
+            MqttSubscriptionManager manager,
+            string topic,
+            ReadOnlySpan<byte> payload,
+            bool retained,
+            DateTime now,
+            bool oversized,
+            ref PayloadJson json)
+        {
+            _manager = manager;
+            _topic = topic;
+            _payload = payload;
+            _retained = retained;
+            _now = now;
+            _oversized = oversized;
+            _json = ref json;
+        }
+
+        public void Visit(MqttTagDefinition def)
+        {
+            if (MqttTopicFilterComparer.Compare(_topic, def.Topic) == MqttTopicFilterCompareResult.IsMatch)
+            {
+                _manager.Deliver(def, _payload, _retained, _now, _oversized, ref _json);
+            }
+        }
+    }
+
    /// <summary>Opaque subscription identity; the diagnostic id names the mode and its topics.</summary>
    /// <param name="DiagnosticId">The human-readable identity surfaced for diagnostics.</param>
    private sealed record MqttSubscriptionHandle(string DiagnosticId) : ISubscriptionHandle;
@@ -1411,7 +1549,8 @@ public sealed class MqttSubscriptionManager
    /// <remarks>
    ///     <b>Two topic indexes, and the difference is load-bearing.</b> Delivery matches an
    ///     <i>incoming published topic</i>, which never carries a wildcard, so it uses
-    ///     <see cref="ByExactTopic"/> (concrete only) plus a comparer scan of <see cref="Wildcards"/>.
+    ///     <see cref="ByExactTopic"/> (concrete only) plus a <see cref="WildcardTrie"/> walk whose candidates the
+    ///     comparer confirms.
    ///     Every path that instead reconstructs state from a <i>subscribed filter string</i> —
    ///     reconnect re-subscribe and per-topic degradation — must use <see cref="ByFilter"/>, which is
    ///     keyed by the tag's authored topic <b>including wildcard patterns</b>, because that is what
@@ -1425,12 +1564,12 @@ public sealed class MqttSubscriptionManager
    ///     included. Keyed the same way <c>_subscribedTopics</c> and SUBACK outcomes are.
    /// </param>
    /// <param name="ByExactTopic">Concrete topic → its definitions; the delivery fast path.</param>
-    /// <param name="Wildcards">Definitions whose authored topic carries an MQTT wildcard.</param>
+    /// <param name="WildcardTrie">Definitions whose authored topic carries an MQTT wildcard, by filter level.</param>
    private sealed record AuthoredTable(
        FrozenDictionary<string, MqttTagDefinition> ByRawPath,
        FrozenDictionary<string, MqttTagDefinition[]> ByFilter,
        FrozenDictionary<string, MqttTagDefinition[]> ByExactTopic,
-        MqttTagDefinition[] Wildcards)
+        TopicFilterTrie<MqttTagDefinition> WildcardTrie)
    {
        public static readonly AuthoredTable Empty =
            Build(new Dictionary<string, MqttTagDefinition>(StringComparer.Ordinal));
@@ -1480,7 +1619,7 @@ public sealed class MqttSubscriptionManager
                byRawPath.ToFrozenDictionary(StringComparer.Ordinal),
                byFilter.ToFrozenDictionary(kv => kv.Key, kv => kv.Value.ToArray(), StringComparer.Ordinal),
                concrete.ToFrozenDictionary(kv => kv.Key, kv => kv.Value.ToArray(), StringComparer.Ordinal),
-                [.. wildcards]);
+                TopicFilterTrie<MqttTagDefinition>.Build(wildcards.Select(d => (d.Topic, d))));
        }
    }
 }
@@ -416,6 +416,11 @@ public sealed class SparkplugIngestor
        _authored = table;
        _warned.Clear();

+        // Bound the shared last-value cache by the CURRENT authored set (R06:M-2): a dropped tag's value
+        // and every non-authored reference's BadNodeIdUnknown marker would otherwise live forever. A
+        // still-authored tag keeps its value, so a redeploy never blanks what has been observed.
+        Values.RetainOnly(table.ByRawPath.ContainsKey);
+
        // Drop state belonging to edge nodes this deploy removed. Without this a tracker (and its
        // rebirth debounce slot) for a node nobody reads survives every future redeploy.
        foreach (var key in _trackers.Keys)
@@ -0,0 +1,152 @@
+using System.Collections.Frozen;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Mqtt;
+
+/// <summary>Receives each candidate a <see cref="TopicFilterTrie{T}"/> match produces.</summary>
+/// <typeparam name="T">The value type stored against each filter.</typeparam>
+internal interface ITopicFilterVisitor<in T>
+{
+    /// <summary>Called once per value whose filter may match the topic.</summary>
+    /// <param name="value">The candidate.</param>
+    void Visit(T value);
+}
+
+/// <summary>
+///     An immutable trie over MQTT topic FILTERS (<c>+</c> / <c>#</c> wildcards), so matching one published
+///     topic costs a walk over its levels instead of a comparer call per wildcard-authored tag (R06:M-6:
+///     the linear scan ran on MQTTnet's shared dispatcher thread for every inbound message).
+/// </summary>
+/// <remarks>
+///     <para>
+///         <b>A candidate generator, not the authority.</b> The trie implements the plain MQTT 3.1.1 §4.7
+///         level rules — <c>+</c> is exactly one level (an empty one included), <c>#</c> is the parent level
+///         and everything under it — and deliberately nothing subtler (the <c>$</c>-topic exclusion, shared
+///         subscriptions). It can therefore only ever return a SUPERSET of the true matches, and every
+///         caller confirms each candidate with MQTTnet's own <c>MqttTopicFilterComparer</c>, the comparer a
+///         broker applies. Semantics stay byte-identical to the scan it replaces; only the work changes.
+///         A differential test pins both halves against that comparer.
+///     </para>
+///     <para>
+///         <b>Allocation-free per match.</b> Levels are walked as spans and looked up through the
+///         dictionary's span alternate lookup; candidates are pushed to a caller-supplied visitor (a
+///         <c>ref struct</c> in production) rather than collected into a list.
+///     </para>
+/// </remarks>
+/// <typeparam name="T">The value type stored against each filter.</typeparam>
+internal sealed class TopicFilterTrie<T>
+{
+    private readonly Node _root;
+
+    private TopicFilterTrie(Node root, int count)
+    {
+        _root = root;
+        Count = count;
+    }
+
+    /// <summary>An empty trie.</summary>
+    public static TopicFilterTrie<T> Empty { get; } = Build([]);
+
+    /// <summary>How many values were inserted.</summary>
+    public int Count { get; }
+
+    /// <summary>Builds a trie from <c>(filter, value)</c> pairs.</summary>
+    /// <param name="entries">The filters and their values.</param>
+    /// <returns>The immutable trie.</returns>
+    public static TopicFilterTrie<T> Build(IEnumerable<(string Filter, T Value)> entries)
+    {
+        var root = new Builder();
+        var count = 0;
+        foreach (var (filter, value) in entries)
+        {
+            var node = root;
+            var levels = filter.Split('/');
+            var terminated = false;
+            for (var i = 0; i < levels.Length; i++)
+            {
+                var level = levels[i];
+                if (level == "#")
+                {
+                    // '#' must be the last level; anything after it is a malformed filter the comparer
+                    // will refuse anyway, so treating '#' as terminal here can only over-generate.
+                    node.Hash.Add(value);
+                    terminated = true;
+                    break;
+                }
+
+                node = level == "+"
+                    ? node.Plus ??= new Builder()
+                    : node.Children.TryGetValue(level, out var child) ? child : node.Children[level] = new Builder();
+            }
+
+            if (!terminated) node.Exact.Add(value);
+            count++;
+        }
+
+        return new TopicFilterTrie<T>(root.Freeze(), count);
+    }
+
+    /// <summary>Pushes every value whose filter may match <paramref name="topic"/> to <paramref name="visitor"/>.</summary>
+    /// <typeparam name="TVisitor">The visitor; a <c>ref struct</c> is allowed.</typeparam>
+    /// <param name="topic">A concrete published topic (never a filter).</param>
+    /// <param name="visitor">Receives each candidate — a superset of the true matches; confirm each one.</param>
+    public void Match<TVisitor>(string topic, ref TVisitor visitor)
+        where TVisitor : ITopicFilterVisitor<T>, allows ref struct
+    {
+        if (Count == 0 || topic is null) return;
+        Walk(_root, topic.AsSpan(), exhausted: false, ref visitor);
+    }
+
+    private static void Walk<TVisitor>(Node node, ReadOnlySpan<char> rest, bool exhausted, ref TVisitor visitor)
+        where TVisitor : ITopicFilterVisitor<T>, allows ref struct
+    {
+        // '#' here covers this level's parent-match AND every deeper level.
+        foreach (var value in node.Hash) visitor.Visit(value);
+
+        if (exhausted)
+        {
+            foreach (var value in node.Exact) visitor.Visit(value);
+            return;
+        }
+
+        var slash = rest.IndexOf('/');
+        var level = slash < 0 ? rest : rest[..slash];
+        var next = slash < 0 ? ReadOnlySpan<char>.Empty : rest[(slash + 1)..];
+        var nextExhausted = slash < 0;
+
+        if (node.Children.Count > 0
+            && node.Children.GetAlternateLookup<ReadOnlySpan<char>>().TryGetValue(level, out var child))
+        {
+            Walk(child, next, nextExhausted, ref visitor);
+        }
+
+        if (node.Plus is { } plus) Walk(plus, next, nextExhausted, ref visitor);
+    }
+
+    private sealed class Node(FrozenDictionary<string, Node> children, Node? plus, T[] exact, T[] hash)
+    {
+        public FrozenDictionary<string, Node> Children { get; } = children;
+
+        public Node? Plus { get; } = plus;
+
+        public T[] Exact { get; } = exact;
+
+        public T[] Hash { get; } = hash;
+    }
+
+    private sealed class Builder
+    {
+        public Dictionary<string, Builder> Children { get; } = new(StringComparer.Ordinal);
+
+        public Builder? Plus { get; set; }
+
+        public List<T> Exact { get; } = [];
+
+        public List<T> Hash { get; } = [];
+
+        public Node Freeze() => new(
+            Children.ToFrozenDictionary(kv => kv.Key, kv => kv.Value.Freeze(), StringComparer.Ordinal),
+            Plus?.Freeze(),
+            [.. Exact],
+            [.. Hash]);
+    }
+}
@@ -48,6 +48,12 @@ internal sealed class SqlBrowseSession : IBrowseSession
    /// <summary>Column alias carrying the SQL type family name.</summary>
    private const string DataTypeColumn = "DATA_TYPE";

+    /// <summary>
+    ///     Column alias carrying <c>YES</c>/<c>NO</c> nullability. Every shipped dialect projects it (Oracle
+    ///     normalises its <c>Y</c>/<c>N</c>); it used to be read by nothing (R06:S-5).
+    /// </summary>
+    private const string IsNullableColumn = "IS_NULLABLE";
+
    /// <summary>The <c>TABLE_TYPE</c> value marking a view rather than a base table.</summary>
    private const string ViewTableType = "VIEW";

@@ -158,7 +164,7 @@ internal sealed class SqlBrowseSession : IBrowseSession
            reference.Schema, reference.Table!, cancellationToken).ConfigureAwait(false);

        // Computed from the columns ALREADY READ for this call — the catalog is not queried a second time.
-        var timestampColumn = PreferredTimestampColumn(columns);
+        var timestampColumn = PreferredTimestampColumn([.. columns.Select(c => (c.Name, c.DataType))]);

        // Ordinal: a column NodeId is only ever minted from this same catalog output, so its case is the
        // catalog's own. A case-insensitive match would pick the wrong column on a case-sensitive collation
@@ -191,7 +197,18 @@ internal sealed class SqlBrowseSession : IBrowseSession
                    Name: column.Name,
                    DriverDataType: _dialect.MapColumnType(column.DataType).ToString(),
                    IsArray: false,
-                    SecurityClass: ReadOnlySecurityClass,
+                    // ⚠ SecurityClass is (ab)used as the picker's descriptor line ("{type} · {SecurityClass}"),
+                    // exactly as the MQTT browser does. Every consumer today is display-only; a future one that
+                    // parses it as SecurityClassification must not read the Sql value (review m-6 — a dedicated
+                    // descriptor field on AttributeInfo is the Commons follow-up). Display only. Nullability is
+                    // what tells an operator a cell can come back NULL, which publishes Uncertain (or Bad under
+                    // nullIsBad), before they commit the tag.
+                    SecurityClass: column.IsNullable switch
+                    {
+                        true => ReadOnlySecurityClass + " · nullable",
+                        false => ReadOnlySecurityClass + " · NOT NULL",
+                        null => ReadOnlySecurityClass,
+                    },
                    IsAlarm: false,
                    AddressFields: addressFields),
            ];
@@ -356,7 +373,7 @@ internal sealed class SqlBrowseSession : IBrowseSession
    ///     than an error: the catalog answering "no rows" is indistinguishable from a genuinely column-less
    ///     relation, and neither is a reason to fail an operator's click.
    /// </summary>
-    private Task<List<(string Name, string DataType)>> ReadColumnsAsync(
+    private Task<List<(string Name, string DataType, bool? IsNullable)>> ReadColumnsAsync(
        string schema, string table, CancellationToken ct) =>
        QueryAsync(
            _dialect.ListColumnsSql,
@@ -367,9 +384,30 @@ internal sealed class SqlBrowseSession : IBrowseSession
            },
            static reader => (
                Name: ReadString(reader, ColumnNameColumn),
-                DataType: ReadOptionalString(reader, DataTypeColumn) ?? string.Empty),
+                DataType: ReadOptionalString(reader, DataTypeColumn) ?? string.Empty,
+                IsNullable: ReadNullability(reader)),
            ct);

+    /// <summary>
+    ///     Reads <c>IS_NULLABLE</c> as a tri-state: <see langword="null"/> when a (custom) dialect does not
+    ///     project it or the value is neither <c>YES</c> nor <c>NO</c> — "unknown" is said by omission, never
+    ///     guessed.
+    /// </summary>
+    private static bool? ReadNullability(DbDataReader reader)
+    {
+        for (var i = 0; i < reader.FieldCount; i++)
+        {
+            if (!string.Equals(reader.GetName(i), IsNullableColumn, StringComparison.OrdinalIgnoreCase)) continue;
+            if (reader.IsDBNull(i)) return null;
+            var text = reader.GetValue(i)?.ToString()?.Trim();
+            if (string.Equals(text, "YES", StringComparison.OrdinalIgnoreCase)) return true;
+            if (string.Equals(text, "NO", StringComparison.OrdinalIgnoreCase)) return false;
+            return null;
+        }
+
+        return null;
+    }
+
    /// <summary>
    ///     Runs one catalog query under the gate and projects every row. The disposed check happens
    ///     <em>inside</em> the gate wait so a dispose racing an in-flight call cannot be missed.
@@ -177,6 +177,31 @@ public interface ISqlDialect
    /// </summary>
    string SingleRowLimitSuffix { get; }

+    /// <summary>
+    ///     The <see cref="SingleRowLimitPrefix"/> position's fragment for an <paramref name="rows"/>-row limit —
+    ///     T-SQL's <c>"TOP (n) "</c>; empty for a dialect that limits at the end. Same trailing-space rule.
+    /// </summary>
+    /// <remarks>
+    ///     Added for the key-value / where-pair row cap (R06:S-1): those plans used to carry no limit, so an
+    ///     ambiguous selector against a history table materialised every matching row on every poll. The
+    ///     planner asks for <c>N + 1</c> rows — one more than the plan can use — so ambiguity stays observable
+    ///     (the reader sees the extra row and publishes a configuration error) without unbounded reads.
+    /// </remarks>
+    /// <param name="rows">The row limit; at least 1.</param>
+    /// <returns>The fragment, possibly empty.</returns>
+    /// <exception cref="ArgumentOutOfRangeException"><paramref name="rows"/> is below 1.</exception>
+    string RowLimitPrefix(int rows);
+
+    /// <summary>
+    ///     The <see cref="SingleRowLimitSuffix"/> position's fragment for an <paramref name="rows"/>-row limit —
+    ///     <c>" LIMIT n"</c> / <c>" FETCH FIRST n ROWS ONLY"</c>; empty for a dialect that limits after
+    ///     <c>SELECT</c>. Same leading-space rule. See <see cref="RowLimitPrefix"/>.
+    /// </summary>
+    /// <param name="rows">The row limit; at least 1.</param>
+    /// <returns>The fragment, possibly empty.</returns>
+    /// <exception cref="ArgumentOutOfRangeException"><paramref name="rows"/> is below 1.</exception>
+    string RowLimitSuffix(int rows);
+
    /// <summary>Catalog query listing schemas — the browser's <c>RootAsync</c> level. Takes no parameters.</summary>
    string ListSchemasSql { get; }

@@ -124,6 +124,21 @@ public sealed class OracleDialect : ISqlDialect
    // statement shape, which this seam deliberately leaves with the planner.
    public string SingleRowLimitSuffix => " FETCH FIRST 1 ROWS ONLY";

+    /// <inheritdoc />
+    public string RowLimitPrefix(int rows)
+    {
+        ArgumentOutOfRangeException.ThrowIfLessThan(rows, 1);
+        return string.Empty;
+    }
+
+    /// <inheritdoc />
+    // The same 12c+ row-limiting clause as SingleRowLimitSuffix; valid after a WHERE with no ORDER BY.
+    public string RowLimitSuffix(int rows)
+    {
+        ArgumentOutOfRangeException.ThrowIfLessThan(rows, 1);
+        return " FETCH FIRST " + rows.ToString(System.Globalization.CultureInfo.InvariantCulture) + " ROWS ONLY";
+    }
+
    /// <inheritdoc />
    // Schemas visible to the connecting principal, from ALL_USERS (Oracle equates a schema with a
    // user), aliased to the TABLE_SCHEMA column name the catalog readers project by.
@@ -86,6 +86,20 @@ public sealed class PostgresDialect : ISqlDialect
    /// <inheritdoc />
    public string SingleRowLimitSuffix => " LIMIT 1";

+    /// <inheritdoc />
+    public string RowLimitPrefix(int rows)
+    {
+        ArgumentOutOfRangeException.ThrowIfLessThan(rows, 1);
+        return string.Empty;
+    }
+
+    /// <inheritdoc />
+    public string RowLimitSuffix(int rows)
+    {
+        ArgumentOutOfRangeException.ThrowIfLessThan(rows, 1);
+        return " LIMIT " + rows.ToString(System.Globalization.CultureInfo.InvariantCulture);
+    }
+
    // The schemas holding relations this connection can actually see, system schemas excluded.
    //
    // Sourced from information_schema.tables, not information_schema.schemata - a deliberate
@@ -87,6 +87,22 @@ public sealed class SqlServerDialect : ISqlDialect
    /// <inheritdoc />
    public string SingleRowLimitSuffix => string.Empty;

+    /// <inheritdoc />
+    // Parenthesised: TOP (n) is the documented modern form, and TOP n without parentheses is the
+    // backwards-compatibility spelling.
+    public string RowLimitPrefix(int rows)
+    {
+        ArgumentOutOfRangeException.ThrowIfLessThan(rows, 1);
+        return "TOP (" + rows.ToString(System.Globalization.CultureInfo.InvariantCulture) + ") ";
+    }
+
+    /// <inheritdoc />
+    public string RowLimitSuffix(int rows)
+    {
+        ArgumentOutOfRangeException.ThrowIfLessThan(rows, 1);
+        return string.Empty;
+    }
+
    /// <inheritdoc/>
    public string ListSchemasSql =>
        "SELECT DISTINCT TABLE_SCHEMA FROM INFORMATION_SCHEMA.TABLES ORDER BY TABLE_SCHEMA";
@@ -28,7 +28,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Sql;
 ///     manufacture an exception to force backoff.</para>
 /// </summary>
 public sealed class SqlDriver
-    : IDriver, ITagDiscovery, IReadable, ISubscribable, IHostConnectivityProbe, ISkippedTagReporter, IAsyncDisposable
+    : IDriver, ITagDiscovery, IReadable, IBatchSubscribable, IHostConnectivityProbe, ISkippedTagReporter, IAsyncDisposable
 {
    /// <summary>Authored tags this driver could not build into its poll table.</summary>
    private readonly SkippedTagLedger _skippedTags = new();
@@ -156,6 +156,16 @@ public sealed class SqlDriver

    private DriverHealth _health = new(DriverState.Unknown, null, null);

+    /// <summary>Guards the lifecycle-generation bump against the generation-checked lifecycle health write.</summary>
+    private readonly object _healthLock = new();
+
+    /// <summary>
+    ///     Bumped by every <see cref="InitializeAsync"/> and <see cref="ShutdownAsync"/>. A lifecycle write from
+    ///     a superseded call, and a poll that STARTED under an older generation (a stale poll outliving the
+    ///     engine's 5 s teardown wait, R06:S-9), can no longer overwrite the newer state.
+    /// </summary>
+    private long _lifecycleGeneration;
+
    /// <summary>
    ///     The exception instance <see cref="ReadAsync"/> has already turned into a health verdict, held only
    ///     until <see cref="HandlePollError"/> — which the poll engine calls with that same object — has
@@ -173,6 +183,9 @@ public sealed class SqlDriver
    /// <summary>Occurs when a subscribed tag's value or quality changes.</summary>
    public event EventHandler<DataChangeEventArgs>? OnDataChange;

+    /// <summary>Occurs once per poll cycle that produced at least one change, carrying every change of that cycle.</summary>
+    public event EventHandler<DataChangeBatchEventArgs>? OnDataChangeBatch;
+
    /// <summary>Occurs when the database endpoint transitions between reachable and unreachable.</summary>
    public event EventHandler<HostStatusChangedEventArgs>? OnHostStatusChanged;

@@ -230,6 +243,9 @@ public sealed class SqlDriver
                OnDataChange?.Invoke(this, new DataChangeEventArgs(handle, tagRef, snapshot)),
            onError: HandlePollError,
            backoffCap: PollBackoffCap,
+            // R02:P1 — one batch per poll burst, so DriverInstanceActor forwards one message per cycle instead
+            // of one per tag (it subscribes exactly one of the two events).
+            onBatch: (handle, items) => OnDataChangeBatch?.Invoke(this, new DataChangeBatchEventArgs(handle, items)),
            // The engine owns no Meter (Core.Abstractions takes no metrics dependency), so this
            // closure IS the production consumer of its overrun signal.
            onOverrun: _ => OtOpcUaTelemetry.PollOverruns.Add(1,
@@ -261,6 +277,10 @@ public sealed class SqlDriver
        _factory = _explicitFactory ?? dialect.Factory;
        _connectionString = connectionString;
        Endpoint = DescribeEndpoint(connectionString);
+
+        // The reader being replaced owns a SemaphoreSlim (R06:S-3). Disposing it is safe even with a stale
+        // poll still inside it: the gate goes only when the last in-flight group releases it.
+        var previous = _reader;
        _reader = new SqlPollReader(
            _factory,
            connectionString,
@@ -271,6 +291,7 @@ public sealed class SqlDriver
            nullIsBad: options.NullIsBad,
            resolve: rawPath => _resolver.TryResolve(rawPath, out var definition) ? definition : null,
            logger: _logger);
+        previous?.Dispose();
    }

    /// <summary>True when the supplied DriverConfig JSON carries a real body. The bootstrapper always passes
@@ -347,20 +368,39 @@ public sealed class SqlDriver
    // identifier.
    public async Task InitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
    {
-        WriteHealth(new DriverHealth(DriverState.Initializing, null, null));
+        var generation = BeginLifecycle();
+        // LastSuccessfulRead is PRESERVED across the lifecycle states — it is the watchdog's evidence clock.
+        WriteHealthIfCurrent(generation, new DriverHealth(DriverState.Initializing, ReadHealth().LastSuccessfulRead, null));

        // adopt a changed config BEFORE the tag table is built, so the table and the connection it
        // will be polled over come from the same revision. ApplyBinding takes the options, dialect and
        // connection string as one unit; adopting options alone would poll a NEW tag set through the OLD
        // database, which is why this driver was excluded from the first pass. A null rebinder (direct
        // construction) or an empty/placeholder document keeps the constructor-supplied trio.
-        if (_rebind is not null && HasConfigBody(driverConfigJson))
+        try
        {
-            var binding = _rebind(driverConfigJson);
-            ApplyBinding(binding.Options, binding.Dialect, binding.ConnectionString);
-        }
+            if (_rebind is not null && HasConfigBody(driverConfigJson))
+            {
+                var binding = _rebind(driverConfigJson);
+                ApplyBinding(binding.Options, binding.Dialect, binding.ConnectionString);
+            }

-        BuildTagTable();
+            BuildTagTable();
+        }
+        catch (Exception ex)
+        {
+            // Review m-4: an unresolvable connectionStringRef or a malformed config threw here AFTER Initializing
+            // was written, and no poll may end Initializing — so the driver latched it with no LastError. Fault
+            // it like the liveness stage does: exception TYPE only on the operator surface (the factory's own
+            // messages are already sanitized, but this method cannot rely on that), full exception to the log.
+            var message =
+                $"Sql driver '{_driverInstanceId}' could not adopt its configuration: {ex.GetType().Name}. " +
+                "Check the connectionStringRef and the driver config JSON.";
+            _logger.LogError(ex, "Sql driver {DriverInstanceId} configuration could not be adopted.", _driverInstanceId);
+            if (WriteHealthIfCurrent(generation, new DriverHealth(DriverState.Faulted, ReadHealth().LastSuccessfulRead, message)))
+                TransitionHostTo(HostState.Stopped);
+            throw;
+        }

        try
        {
@@ -369,7 +409,7 @@ public sealed class SqlDriver
        catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
        {
            // The caller tore the initialization down; not a database verdict.
-            WriteHealth(new DriverHealth(DriverState.Unknown, null, null));
+            WriteHealthIfCurrent(generation, new DriverHealth(DriverState.Unknown, ReadHealth().LastSuccessfulRead, null));
            throw;
        }
        catch (Exception ex)
@@ -385,8 +425,8 @@ public sealed class SqlDriver
                $"Check the database is reachable and the connection string is valid.";
            _logger.LogError(ex, "Sql driver {DriverInstanceId} liveness check against {Endpoint} failed.",
                _driverInstanceId, Endpoint);
-            WriteHealth(new DriverHealth(DriverState.Faulted, null, message));
-            TransitionHostTo(HostState.Stopped);
+            if (WriteHealthIfCurrent(generation, new DriverHealth(DriverState.Faulted, ReadHealth().LastSuccessfulRead, message)))
+                TransitionHostTo(HostState.Stopped);
            throw new InvalidOperationException(message, ex);
        }

@@ -399,7 +439,7 @@ public sealed class SqlDriver
        }
        catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
        {
-            WriteHealth(new DriverHealth(DriverState.Unknown, null, null));
+            WriteHealthIfCurrent(generation, new DriverHealth(DriverState.Unknown, ReadHealth().LastSuccessfulRead, null));
            throw;
        }
        catch (Exception ex)
@@ -415,13 +455,13 @@ public sealed class SqlDriver
            _logger.LogError(ex,
                "Sql driver {DriverInstanceId} catalog validation against {Endpoint} failed.",
                _driverInstanceId, Endpoint);
-            WriteHealth(new DriverHealth(DriverState.Faulted, null, message));
-            TransitionHostTo(HostState.Stopped);
+            if (WriteHealthIfCurrent(generation, new DriverHealth(DriverState.Faulted, ReadHealth().LastSuccessfulRead, message)))
+                TransitionHostTo(HostState.Stopped);
            throw new InvalidOperationException(message, ex);
        }

-        WriteHealth(new DriverHealth(DriverState.Healthy, DateTime.UtcNow, null));
-        TransitionHostTo(HostState.Running);
+        if (WriteHealthIfCurrent(generation, new DriverHealth(DriverState.Healthy, DateTime.UtcNow, null)))
+            TransitionHostTo(HostState.Running);
        _logger.LogInformation(
            "Sql driver {DriverInstanceId} initialized against {Endpoint} with {TagCount} authored tag(s).",
            _driverInstanceId, Endpoint, Tags.Count);
@@ -437,9 +477,10 @@ public sealed class SqlDriver
    /// <inheritdoc />
    public async Task ShutdownAsync(CancellationToken cancellationToken)
    {
+        var generation = BeginLifecycle();
        var lastRead = ReadHealth().LastSuccessfulRead;
        await TeardownAsync().ConfigureAwait(false);
-        WriteHealth(new DriverHealth(DriverState.Unknown, lastRead, null));
+        WriteHealthIfCurrent(generation, new DriverHealth(DriverState.Unknown, lastRead, null));
    }

    /// <inheritdoc />
@@ -512,11 +553,37 @@ public sealed class SqlDriver
        // unreachable" and degrade a perfectly healthy driver.
        ArgumentNullException.ThrowIfNull(fullReferences);

+        // The generation this read started under: if a Shutdown/Initialize lands while it is in flight, its
+        // verdict describes a superseded configuration and must not touch the newer health (R06:S-9).
+        var generation = Interlocked.Read(ref _lifecycleGeneration);
+        return await ReadThroughAsync(_reader, fullReferences, generation, cancellationToken).ConfigureAwait(false);
+    }
+
+    /// <summary>
+    ///     <see cref="ReadAsync"/>'s body against a specific reader — the one the caller captured. Internal so a
+    ///     test can drive the "reader replaced between capture and use" race deterministically.
+    /// </summary>
+    internal async Task<IReadOnlyList<DataValueSnapshot>> ReadThroughAsync(
+        SqlPollReader reader, IReadOnlyList<string> fullReferences, long generation, CancellationToken cancellationToken)
+    {
        try
        {
-            var snapshots = await _reader.ReadAsync(fullReferences, cancellationToken).ConfigureAwait(false);
-            ObservePollOutcome(snapshots);
-            return snapshots;
+            var result = await reader.ReadDetailedAsync(fullReferences, cancellationToken).ConfigureAwait(false);
+            ObservePollOutcome(result.Snapshots, result.AnsweredRefusalGroups, generation);
+            return result.Snapshots;
+        }
+        catch (SqlPollReaderDisposedException ex) when (!cancellationToken.IsCancellationRequested)
+        {
+            // A rebind swapped the reader under this poll (review m-1: a redeploy re-initialises without
+            // teardown, so the engine keeps polling). Retry ONCE on the current reader; if there is no newer
+            // one (the driver itself was disposed), hand the engine an exception it is told not to classify —
+            // it used to Degrade the driver as "poll failed: OperationCanceledException".
+            var current = Volatile.Read(ref _reader);
+            if (!ReferenceEquals(current, reader))
+                return await ReadThroughAsync(current, fullReferences, generation, cancellationToken).ConfigureAwait(false);
+
+            Volatile.Write(ref _classifiedByRead, ex);
+            throw;
        }
        catch (OperationCanceledException)
        {
@@ -530,8 +597,12 @@ public sealed class SqlDriver
                _driverInstanceId, Endpoint);
            // Type name only — never ex.Message (see InitializeAsync for why); the full exception is already
            // on the log sink via the LogWarning exception parameter above.
-            Degrade($"Sql driver '{_driverInstanceId}' could not reach {Endpoint}: {ex.GetType().Name}.");
-            TransitionHostTo(HostState.Stopped);
+            if (IsCurrentLifecycle(generation))
+            {
+                Degrade($"Sql driver '{_driverInstanceId}' could not reach {Endpoint}: {ex.GetType().Name}.");
+                TransitionHostTo(HostState.Stopped);
+            }
+
            // Mark THIS exception object as already classified before it goes back to the poll engine, which
            // routes it to HandlePollError next. The mark is what makes the deferral there exact — see that
            // method for why inferring it from the exception's type was not.
@@ -603,9 +674,21 @@ public sealed class SqlDriver
    ///     cadence rather than backed off from.</para>
    /// </summary>
    /// <param name="snapshots">The snapshots the reader returned for one poll.</param>
-    internal void ObservePollOutcome(IReadOnlyList<DataValueSnapshot> snapshots)
+    /// <param name="answeredRefusals">
+    ///     Groups the database answered but the driver refused (an over-cap result set, R06:S-1). Their
+    ///     members carry <see cref="SqlStatusCodes.BadConfigurationError"/>, which alone is not answer evidence
+    ///     (the planner mints it before any I/O), so the count is what makes them count as the database
+    ///     answering.
+    /// </param>
+    /// <param name="generation">
+    ///     The lifecycle generation the poll started under; a superseded one is ignored outright. Null (tests)
+    ///     means "current".
+    /// </param>
+    internal void ObservePollOutcome(
+        IReadOnlyList<DataValueSnapshot> snapshots, int answeredRefusals = 0, long? generation = null)
    {
        if (snapshots.Count == 0) return;
+        if (generation is { } started && !IsCurrentLifecycle(started)) return;

        var good = 0;
        var unreachable = 0;
@@ -620,6 +703,8 @@ public sealed class SqlDriver
            if (IsAnswerEvidence(snapshot.StatusCode)) answered++;
        }

+        answered += answeredRefusals;
+
        if (unreachable > 0)
        {
            Degrade(
@@ -655,17 +740,12 @@ public sealed class SqlDriver

        if (answered == 0) return;   // authoring-class Bad only — not a statement about the database.

-        if (good == 0)
-        {
-            // The database answered, just not with a value: an absent row, a NULL cell, a cell that would
-            // not coerce. Those are data/authoring facts, so the health STATE is deliberately left exactly
-            // as it was — but they are still proof the transport works, and the evidence clock the
-            // comms-loss watchdog reads must say so.
-            TouchLastSuccessfulRead();
-            TransitionHostTo(HostState.Running);
-            return;
-        }

+        // Good values, OR a database that answered with refusals only — an absent row, a NULL cell, an
+        // uncoercible cell, an over-cap result set. A refusal is the database answering: it advances the
+        // evidence clock AND restores Healthy after a comms fault, exactly as a Good read does. Leaving the
+        // state as it was latched a recovered database Degraded behind every poll that read only refusals.
+        //
        // Route through the Faulted guard, not a raw WriteHealth: a poll still in flight when a concurrent
        // ReinitializeAsync has recorded Faulted (the engine's ~5 s teardown wait is shorter than the 15 s
        // default operationTimeout, so a stale poll can still complete afterwards) must not flip Faulted back
@@ -792,7 +872,11 @@ public sealed class SqlDriver
    /// </summary>
    /// <param name="project">Builds the snapshot to publish from the current one.</param>
    private void UpdateHealthUnlessFaulted(Func<DriverHealth, DriverHealth> project)
-        => UpdateHealth(current => current.State == DriverState.Faulted ? null : project(current));
+        // Initializing too: only the initialize's own final write may end it — a poll landing mid-init
+        // (a re-init without shutdown keeps the engine running) used to flip Initializing → Healthy.
+        => UpdateHealth(current => current.State is DriverState.Faulted or DriverState.Initializing
+            ? null
+            : project(current));

    /// <summary>
    ///     The one read-modify-write of the health field, as a compare-and-swap retry loop.
@@ -823,13 +907,31 @@ public sealed class SqlDriver
    /// <summary>Barrier-protected read of the multi-threaded health field.</summary>
    private DriverHealth ReadHealth() => Volatile.Read(ref _health);

+    /// <summary>Starts a lifecycle operation and returns its generation; every later one supersedes it.</summary>
+    private long BeginLifecycle()
+    {
+        lock (_healthLock) return ++_lifecycleGeneration;
+    }
+
+    /// <summary>Whether <paramref name="generation"/> is still the newest lifecycle operation.</summary>
+    private bool IsCurrentLifecycle(long generation) => Interlocked.Read(ref _lifecycleGeneration) == generation;
+
+    /// <summary>The current lifecycle generation. Test observation of the S-9 guard.</summary>
+    internal long LifecycleGenerationForTests => Interlocked.Read(ref _lifecycleGeneration);
+
    /// <summary>
-    ///     Unconditional publish of a new health snapshot, for the lifecycle transitions that are
-    ///     last-writer-wins by definition (Initialize / Shutdown). Everything driven by a poll goes through
-    ///     <see cref="UpdateHealth"/> instead, because it has to read the current snapshot first.
+    ///     A lifecycle write that applies only while <paramref name="generation"/> is current — atomic against
+    ///     <see cref="BeginLifecycle"/>, so a superseded initialize/shutdown never overwrites a newer one.
    /// </summary>
-    /// <param name="value">The health snapshot to publish.</param>
-    private void WriteHealth(DriverHealth value) => Volatile.Write(ref _health, value);
+    private bool WriteHealthIfCurrent(long generation, DriverHealth value)
+    {
+        lock (_healthLock)
+        {
+            if (_lifecycleGeneration != generation) return false;
+            Volatile.Write(ref _health, value);
+            return true;
+        }
+    }

    /// <summary>Records a host-state change and raises <see cref="OnHostStatusChanged"/> — on transitions only.</summary>
    private void TransitionHostTo(HostState newState)
@@ -867,10 +969,15 @@ public sealed class SqlDriver
                    table[entry.RawPath] = definition;
                else
                {
-                    blobSkips.Add(new SkippedTag(entry.RawPath, "TagConfig did not map to a definition"));
+                    // The reason is the DEPLOY GATE's own explanation (R06:S-4) — SqlTagDefinitionFactory.Inspect
+                    // asks this same parser and then says why — so /hosts names e.g. the deferred Query model
+                    // instead of a generic "did not map" for a tag the gate already warned about.
+                    var reason = SqlTagDefinitionFactory.Inspect(entry.TagConfig).FirstOrDefault()
+                                 ?? "TagConfig did not map to a definition";
+                    blobSkips.Add(new SkippedTag(entry.RawPath, reason));
                    _logger.LogWarning(
-                        "Sql tag config did not map to a definition; skipping. Driver={DriverInstanceId} RawPath={RawPath}",
-                        _driverInstanceId, entry.RawPath);
+                        "Sql tag config did not map to a definition; skipping. Driver={DriverInstanceId} RawPath={RawPath} Reason={Reason}",
+                        _driverInstanceId, entry.RawPath, reason);
                }
            }
            catch (Exception ex)
@@ -1150,7 +1257,20 @@ public sealed class SqlDriver
    ///     <c>await using</c> does not leak the poll loops.
    /// </summary>
    /// <returns>A task that represents the asynchronous operation.</returns>
-    public async ValueTask DisposeAsync() => await TeardownAsync().ConfigureAwait(false);
+    public async ValueTask DisposeAsync()
+    {
+        await TeardownAsync().ConfigureAwait(false);
+
+        // Only on the FINAL dispose: a Shutdown → Initialize cycle on the same instance keeps polling
+        // through this reader when the init does not rebind (no rebinder / placeholder config).
+        _reader.Dispose();
+    }
+
+    /// <summary>Re-runs <see cref="ApplyBinding"/> on the current binding — a real reader swap, for the m-1 race test.</summary>
+    internal void RebindForTests() => ApplyBinding(_options, _dialect, _connectionString);
+
+    /// <summary>The live poll reader. Test observation of the S-3 lifecycle only.</summary>
+    internal SqlPollReader ReaderForTests => _reader;

    /// <summary>
    ///     Shared teardown: stops every polled subscription and drops the authored table. Idempotent — safe
@@ -194,8 +194,14 @@ public static class SqlDriverFactoryExtensions
        }
        catch (JsonException ex)
        {
+            // The parser's message AND the exception carrying it are withheld (R06:S-8), matching
+            // SqlDriverProbe and SqlDriverBrowser: System.Text.Json quotes the offending token, and a pasted
+            // connection-string literal is exactly the malformed text that lands here. This message becomes
+            // InitializeFailed -> health LastError -> /hosts. Line/byte position carry no content, so they stay.
            throw new InvalidOperationException(
-                $"Sql driver config for '{driverInstanceId}' is not valid JSON: {ex.Message}", ex);
+                $"Sql driver config for '{driverInstanceId}' is not valid JSON (line "
+                + $"{(ex.LineNumber is { } line ? line + 1 : (object)"?")}, byte {ex.BytePositionInLine?.ToString(System.Globalization.CultureInfo.InvariantCulture) ?? "?"}). The parser's message is withheld because the malformed text may "
+                + "carry a connection string.");
        }
    }

@@ -230,15 +230,23 @@ public static class SqlGroupPlanner
            values.Add(keyValue);
        }

+        // Row cap (R06:S-1): one row per distinct key is all this plan can use. It reads up to TWICE that, so a
+        // handful of stray duplicates stays inside the cap and is attributed PER KEY by the reader (only the
+        // duplicated key's tags go BadConfigurationError) — and asks for one row more than that, so only a
+        // gross excess (a history/events table, unattributable by construction because the rest is unread)
+        // fails the whole group. Memory stays O(keys) either way.
+        var rowCap = values.Count * 2;
        var sql = new StringBuilder("SELECT ")
+            .Append(dialect.RowLimitPrefix(rowCap + 1))
            .Append(QuoteList(selected, dialect))
            .Append(" FROM ").Append(QuoteQualifiedName(first.Table, dialect))
            .Append(" WHERE ").Append(dialect.QuoteIdentifier(keyColumn))
            .Append(" IN (").AppendJoin(", ", markers).Append(')')
+            .Append(dialect.RowLimitSuffix(rowCap + 1))
            .ToString();

        return new SqlQueryPlan(
-            SqlTagModel.KeyValue, groupKey, sql, markers, bindNames, values, members, selected);
+            SqlTagModel.KeyValue, groupKey, sql, markers, bindNames, values, members, selected, rowCap);
    }

    /// <summary>
@@ -270,14 +278,18 @@ public static class SqlGroupPlanner
        // A where-pair wins over topByTimestamp; the parser already guarantees exactly one is populated.
        if (!Blank(first.RowSelectorColumn) && first.RowSelectorValue is not null)
        {
+            // Capped at TWO rows (R06:S-1): the selector must identify one row, and the second is the proof it
+            // does not. A TOP 1 alone would hide that ambiguity (see SqlPollReader.SelectWideRow); no cap at all
+            // materialised every matching row of an events table on every poll.
            var marker = dialect.ParameterMarker(RowSelectorBaseName);
            var sql = string.Concat(
-                "SELECT ", columns, " FROM ", table,
-                " WHERE ", dialect.QuoteIdentifier(first.RowSelectorColumn!), " = ", marker);
+                "SELECT ", dialect.RowLimitPrefix(2), columns, " FROM ", table,
+                " WHERE ", dialect.QuoteIdentifier(first.RowSelectorColumn!), " = ", marker,
+                dialect.RowLimitSuffix(2));
            return new SqlQueryPlan(
                SqlTagModel.WideRow, groupKey, sql,
                [marker], [dialect.ParameterBindName(RowSelectorBaseName)],
-                [first.RowSelectorValue], members, selected);
+                [first.RowSelectorValue], members, selected, RowCap: 1);
        }

        if (!Blank(first.RowSelectorTopByTimestamp))
@@ -1,5 +1,7 @@
+using System.Collections.Concurrent;
 using System.Data.Common;
 using System.Diagnostics;
+using System.Runtime.CompilerServices;
 using System.Globalization;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
@@ -36,7 +38,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Sql;
 ///     no subscription state and no connection between polls, so the driver shell can wrap it in
 ///     <see cref="PollGroupEngine"/> and own those concerns.</para>
 /// </summary>
-public sealed class SqlPollReader
+public sealed class SqlPollReader : IDisposable
 {
    /// <summary>Minimum spacing between "your source violates the query contract" warnings, per reader.</summary>
    private static readonly TimeSpan ContractWarningInterval = TimeSpan.FromMinutes(1);
@@ -52,13 +54,41 @@ public sealed class SqlPollReader

    /// <summary>
    ///     Caps concurrently executing group queries — and therefore concurrently held connections
-    ///     (design §8.4). Never disposed: a <see cref="SemaphoreSlim"/> only needs disposal once its
-    ///     <c>AvailableWaitHandle</c> has been touched, and not disposing it also removes the hazard of a
-    ///     timed-out-but-still-running group releasing into a disposed semaphore.
+    ///     (design §8.4). Disposed by <see cref="Dispose"/> only once every group that ever acquired it has
+    ///     released it (<see cref="_refs"/>), so a timed-out-but-still-running group can never release into a
+    ///     disposed semaphore (R06:S-3 — it used to be never disposed, one per reinitialize).
    /// </summary>
    private readonly SemaphoreSlim _gate;

-    private long _lastContractWarningTicks;
+    /// <summary>
+    ///     Owner reference (1) plus one per in-flight group. <see cref="Dispose"/> drops the owner's; whoever
+    ///     takes it to zero disposes <see cref="_gate"/>. Zero is terminal — no group can start after it.
+    /// </summary>
+    private int _refs = 1;
+
+    private int _disposed;
+
+
+    /// <summary>
+    ///     Per-key last-warned instant for the per-poll warnings (R06:S-6): a frozen group's BadTimeout and a
+    ///     failing group's query error used to log every poll, per group, indefinitely — 20 groups at 1 s was
+    ///     20 lines a second carrying SQL text. Keyed by the plan's SQL text, so bounded by the plan count.
+    /// </summary>
+    private readonly ConcurrentDictionary<string, long> _lastWarnedTicks = new(StringComparer.Ordinal);
+
+    /// <summary>Tags whose uncoercible cell has been warned about — once per tag per reader (the refusal rule).</summary>
+    private readonly ConcurrentDictionary<string, byte> _coerceWarned = new(StringComparer.Ordinal);
+
+    /// <summary>
+    ///     The resolved definitions, slot map and plans for each reference list a caller polls (R06:S-7). A
+    ///     poll loop passes the SAME list instance every cycle, so it is planned once instead of every poll.
+    ///     Weakly keyed: an unsubscribed list (and its entry) is collected with it. Invalidation is structural —
+    ///     each entry remembers the definition INSTANCES it was built from, and any reference resolving to a
+    ///     different instance (a catalog-gate swap) rebuilds it.
+    /// </summary>
+    private readonly ConditionalWeakTable<IReadOnlyList<string>, PollShape> _shapes = new();
+
+    private int _plansBuilt;

    /// <summary>Initializes a new instance of the <see cref="SqlPollReader"/> class.</summary>
    /// <param name="factory">
@@ -154,26 +184,87 @@ public sealed class SqlPollReader
    /// <exception cref="DbException">The database could not be reached (opening a connection failed).</exception>
    public async Task<IReadOnlyList<DataValueSnapshot>> ReadAsync(
        IReadOnlyList<string> fullReferences, CancellationToken cancellationToken)
+        => (await ReadDetailedAsync(fullReferences, cancellationToken).ConfigureAwait(false)).Snapshots;
+
+    /// <summary>
+    ///     <see cref="ReadAsync"/> plus what the snapshots alone cannot say: how many groups the database
+    ///     ANSWERED with more rows than the plan can use (R06:S-1). Those groups publish
+    ///     <see cref="SqlStatusCodes.BadConfigurationError"/> — the same code an un-plannable definition gets
+    ///     before any I/O — so the driver needs this count to treat them as the answer evidence they are.
+    /// </summary>
+    /// <param name="fullReferences">The RawPaths to read.</param>
+    /// <param name="cancellationToken">The caller's token; see <see cref="ReadAsync"/>.</param>
+    /// <returns>The snapshots and the answered-refusal count.</returns>
+    public async Task<SqlPollResult> ReadDetailedAsync(
+        IReadOnlyList<string> fullReferences, CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(fullReferences);

        var results = new DataValueSnapshot[fullReferences.Count];
-        if (results.Length == 0) return results;
+        if (results.Length == 0) return new SqlPollResult(results, 0);

        var readAt = DateTime.UtcNow;
+        var shape = GetShape(fullReferences);

-        // Resolve first. A miss is this tag's own problem (BadNodeIdUnknown) and must not reach the planner,
-        // whose members are the sole thing the slice-back walks.
+        // A miss is this tag's own problem (BadNodeIdUnknown) and never reaches the planner, whose members
+        // are the sole thing the slice-back walks.
+        for (var i = 0; i < shape.Resolved.Length; i++)
+        {
+            if (shape.Resolved[i] is null)
+                results[i] = new DataValueSnapshot(null, SqlStatusCodes.BadNodeIdUnknown, null, readAt);
+        }
+
+        var answeredRefusals = shape.Definitions.Count > 0
+            ? await ReadGroupsAsync(shape, results, readAt, cancellationToken).ConfigureAwait(false)
+            : 0;
+
+        // Fail-safe. Nothing above should leave a hole, but "N in, N out" is a contract the caller indexes
+        // blind — a null here would be a NullReferenceException in the publish fan-out, far from its cause.
+        for (var i = 0; i < results.Length; i++)
+            results[i] ??= new DataValueSnapshot(null, SqlStatusCodes.BadInternalError, null, readAt);
+
+        return new SqlPollResult(results, answeredRefusals);
+    }
+
+    /// <summary>How many times a reference list has been (re)planned. Test observation of the S-7 cache.</summary>
+    internal int PlansBuiltForTests => Volatile.Read(ref _plansBuilt);
+
+    /// <summary>
+    ///     Returns the cached shape for <paramref name="fullReferences"/>, rebuilding it when any reference now
+    ///     resolves to a different definition instance than the one it was built from.
+    /// </summary>
+    private PollShape GetShape(IReadOnlyList<string> fullReferences)
+    {
+        if (_shapes.TryGetValue(fullReferences, out var cached) && cached.Resolved.Length == fullReferences.Count)
+        {
+            var current = true;
+            for (var i = 0; i < fullReferences.Count && current; i++)
+            {
+                var definition = fullReferences[i] is { } reference ? _resolve(reference) : null;
+                current = ReferenceEquals(definition, cached.Resolved[i]);
+            }
+
+            if (current) return cached;
+        }
+
+        var shape = BuildShape(fullReferences);
+        _shapes.AddOrUpdate(fullReferences, shape);
+        return shape;
+    }
+
+    /// <summary>Resolves, slots and plans one reference list.</summary>
+    private PollShape BuildShape(IReadOnlyList<string> fullReferences)
+    {
+        Interlocked.Increment(ref _plansBuilt);
+
+        var resolved = new SqlTagDefinition?[fullReferences.Count];
        var definitions = new List<SqlTagDefinition>(fullReferences.Count);
        var slots = new Dictionary<SqlTagDefinition, List<int>>();
        for (var i = 0; i < fullReferences.Count; i++)
        {
            var definition = fullReferences[i] is { } reference ? _resolve(reference) : null;
-            if (definition is null)
-            {
-                results[i] = new DataValueSnapshot(null, SqlStatusCodes.BadNodeIdUnknown, null, readAt);
-                continue;
-            }
+            resolved[i] = definition;
+            if (definition is null) continue;

            definitions.Add(definition);
            if (!slots.TryGetValue(definition, out var positions))
@@ -181,45 +272,54 @@ public sealed class SqlPollReader
            positions.Add(i);
        }

-        if (definitions.Count > 0)
-            await ReadGroupsAsync(definitions, slots, results, readAt, cancellationToken).ConfigureAwait(false);
+        if (definitions.Count == 0) return new PollShape(resolved, definitions, slots, [], PlanningFailed: false);

-        // Fail-safe. Nothing above should leave a hole, but "N in, N out" is a contract the caller indexes
-        // blind — a null here would be a NullReferenceException in the publish fan-out, far from its cause.
-        for (var i = 0; i < results.Length; i++)
-            results[i] ??= new DataValueSnapshot(null, SqlStatusCodes.BadInternalError, null, readAt);
-
-        return results;
-    }
-
-    /// <summary>Plans the resolved definitions, runs every group concurrently, and slices the results back.</summary>
-    private async Task ReadGroupsAsync(
-        List<SqlTagDefinition> definitions,
-        Dictionary<SqlTagDefinition, List<int>> slots,
-        DataValueSnapshot[] results,
-        DateTime readAt,
-        CancellationToken cancellationToken)
-    {
-        IReadOnlyList<SqlQueryPlan> plans;
        try
        {
-            plans = SqlGroupPlanner.Plan(definitions, _dialect);
+            return new PollShape(resolved, definitions, slots, SqlGroupPlanner.Plan(definitions, _dialect), PlanningFailed: false);
        }
        catch (Exception ex) when (ex is ArgumentException or NotSupportedException)
        {
            // A definition with a broken invariant — SqlEquipmentTagParser rejects all of these up front, so
            // reaching here means a definition was built past the parser. It is an authoring fault, not a
            // database fault: Bad-code the planned tags rather than throwing and triggering connection backoff.
+            // Logged once per (re)plan, which the cache makes once per shape rather than once per poll.
            _logger.LogError(ex, "Sql poll planning failed for {Count} tag(s); publishing BadConfigurationError.",
                definitions.Count);
-            foreach (var definition in definitions)
+            return new PollShape(resolved, definitions, slots, [], PlanningFailed: true);
+        }
+    }
+
+    /// <summary>One reference list's resolved definitions, slot map and plans — immutable once built.</summary>
+    private sealed record PollShape(
+        SqlTagDefinition?[] Resolved,
+        List<SqlTagDefinition> Definitions,
+        Dictionary<SqlTagDefinition, List<int>> Slots,
+        IReadOnlyList<SqlQueryPlan> Plans,
+        bool PlanningFailed);
+
+    /// <summary>
+    ///     Runs every planned group concurrently and slices the results back. Returns how many groups came
+    ///     back with an answered refusal (over the row cap, or a duplicated key).
+    /// </summary>
+    private async Task<int> ReadGroupsAsync(
+        PollShape shape,
+        DataValueSnapshot[] results,
+        DateTime readAt,
+        CancellationToken cancellationToken)
+    {
+        var slots = shape.Slots;
+        var plans = shape.Plans;
+        if (shape.PlanningFailed)
+        {
+            foreach (var definition in shape.Definitions)
            {
                if (!slots.TryGetValue(definition, out var positions)) continue;
                var snapshot = new DataValueSnapshot(null, SqlStatusCodes.BadConfigurationError, null, readAt);
                foreach (var position in positions) results[position] = snapshot;
            }

-            return;
+            return 0;
        }

        // Groups run concurrently; _gate — not the task count — is what bounds open connections. Each group
@@ -233,8 +333,18 @@ public sealed class SqlPollReader
        // leaves a sibling group running against a connection nobody is watching.
        var outcomes = await Task.WhenAll(groups).ConfigureAwait(false);

+        // Surfaced AFTER WhenAll, as one typed exception: a group throwing it would turn WhenAll into a plain
+        // TaskCanceledException and the caller could no longer tell "superseded reader" from a caller cancel.
+        if (outcomes.Any(o => ReferenceEquals(o, GroupResult.ReaderDisposed))) throw new SqlPollReaderDisposedException();
+
+        var answeredRefusals = 0;
        for (var g = 0; g < plans.Count; g++)
-            Slice(plans[g], outcomes[g], slots, results, readAt);
+        {
+            var refusedSome = Slice(plans[g], outcomes[g], slots, results, readAt);
+            if (refusedSome || ReferenceEquals(outcomes[g], GroupResult.RowCapExceeded)) answeredRefusals++;
+        }
+
+        return answeredRefusals;
    }

    /// <summary>
@@ -273,6 +383,22 @@ public sealed class SqlPollReader
    ///     inside the deadline, so a poll behind a wedged group still returns on time — as BadTimeout.</para>
    /// </summary>
    private async Task<GroupResult> RunGroupAsync(SqlQueryPlan plan, CancellationToken cancellationToken)
+    {
+        // A reader replaced by a reinitialize (and disposed) can still be holding a stale poll: it runs no
+        // new group. Cancellation is the honest answer — the poll that asked has been superseded.
+        if (!TryAddRef()) return GroupResult.ReaderDisposed;
+
+        try
+        {
+            return await RunGroupCoreAsync(plan, cancellationToken).ConfigureAwait(false);
+        }
+        finally
+        {
+            ReleaseRef();
+        }
+    }
+
+    private async Task<GroupResult> RunGroupCoreAsync(SqlQueryPlan plan, CancellationToken cancellationToken)
    {
        var clock = Stopwatch.StartNew();

@@ -288,6 +414,9 @@ public sealed class SqlPollReader
            if (budget <= TimeSpan.Zero) return GroupResult.TimedOut;
            deadline.CancelAfter(budget);

+            // The work holds its OWN reference: it can outlive this method (a timed-out group is abandoned
+            // still running) and its finally releases the slot into _gate, which must therefore still exist.
+            AddRefForWork();
            work = Task.Run(
                async () =>
                {
@@ -299,6 +428,7 @@ public sealed class SqlPollReader
                    {
                        _gate.Release();
                        deadline.Dispose();
+                        ReleaseRef();
                    }
                },
                CancellationToken.None);
@@ -334,6 +464,41 @@ public sealed class SqlPollReader
        }
    }

+    /// <summary>
+    ///     Releases the concurrency gate once no group still holds it. Idempotent; safe while groups are in
+    ///     flight (the last one out disposes it). A disposed reader starts no new group.
+    /// </summary>
+    public void Dispose()
+    {
+        if (Interlocked.Exchange(ref _disposed, 1) == 0) ReleaseRef();
+    }
+
+    /// <summary>True once <see cref="_gate"/> has actually been disposed. Test observation only.</summary>
+    internal bool GateDisposedForTests => Volatile.Read(ref _refs) == 0;
+
+    /// <summary>Takes a reference unless the reader is already fully released.</summary>
+    private bool TryAddRef()
+    {
+        while (true)
+        {
+            // A disposed reader starts no new group even while older ones are still in flight (review m-2):
+            // the gate would survive until they finish, but a replaced reader must not take new work.
+            if (Volatile.Read(ref _disposed) != 0) return false;
+            var current = Volatile.Read(ref _refs);
+            if (current == 0) return false;
+            if (Interlocked.CompareExchange(ref _refs, current + 1, current) == current) return true;
+        }
+    }
+
+    /// <summary>A further reference for work started under an already-held one (so never from zero).</summary>
+    private void AddRefForWork() => Interlocked.Increment(ref _refs);
+
+    /// <summary>Drops a reference; the one that reaches zero disposes the gate.</summary>
+    private void ReleaseRef()
+    {
+        if (Interlocked.Decrement(ref _refs) == 0) _gate.Dispose();
+    }
+
    /// <summary>How much of this group's <c>operationTimeout</c> budget is left; never negative.</summary>
    private TimeSpan Remaining(Stopwatch clock)
    {
@@ -346,11 +511,14 @@ public sealed class SqlPollReader
    {
        // The table is named for the same reason the contract warnings name it: under a partial outage this
        // line repeats every poll, and "which source is frozen" is the only question the operator has.
-        _logger.LogWarning(
-            "Sql poll group ({Model}, '{Table}', {Members} tag(s)) exceeded the {Timeout} ms operation " +
-            "timeout; publishing BadTimeout.",
-            plan.Model, plan.Members[0].Table, plan.Members.Count,
-            (int)_operationTimeout.TotalMilliseconds);
+        if (ShouldWarn("timeout:" + plan.SqlText))
+        {
+            _logger.LogWarning(
+                "Sql poll group ({Model}, '{Table}', {Members} tag(s)) exceeded the {Timeout} ms operation " +
+                "timeout; publishing BadTimeout. Repeats for this group are suppressed for {Interval} s.",
+                plan.Model, plan.Members[0].Table, plan.Members.Count,
+                (int)_operationTimeout.TotalMilliseconds, (int)ContractWarningInterval.TotalSeconds);
+        }

        AbandonedTask.Detach(work);
        return GroupResult.TimedOut;
@@ -412,9 +580,13 @@ public sealed class SqlPollReader
            {
                // The connection opened, so the server is up — this query is what failed (an identifier that
                // is not in the catalog, a lock, a permission). That is this group's problem alone.
-                _logger.LogWarning(
-                    ex, "Sql poll group ({Model}, {Members} tag(s)) failed: {Sql}",
-                    plan.Model, plan.Members.Count, plan.SqlText);
+                if (ShouldWarn("failed:" + plan.SqlText))
+                {
+                    _logger.LogWarning(
+                        ex, "Sql poll group ({Model}, {Members} tag(s)) failed: {Sql}. Repeats for this group are " +
+                        "suppressed for {Interval} s.",
+                        plan.Model, plan.Members.Count, plan.SqlText, (int)ContractWarningInterval.TotalSeconds);
+                }
                return GroupResult.Failed;
            }
        }
@@ -442,8 +614,11 @@ public sealed class SqlPollReader
            columnIndex[selected[c]] = c;
        }

+        // The client-side half of the row cap (R06:S-1): the statement already asks for RowCap + 1 rows, but a
+        // provider that cannot spell a limit must not turn that into an unbounded read either.
+        var limit = plan.RowCap is { } cap ? cap + 1 : int.MaxValue;
        var rows = new List<object?[]>();
-        while (await reader.ReadAsync(cancellationToken).ConfigureAwait(false))
+        while (rows.Count < limit && await reader.ReadAsync(cancellationToken).ConfigureAwait(false))
        {
            var row = new object?[selected.Count];
            for (var c = 0; c < selected.Count; c++)
@@ -451,6 +626,27 @@ public sealed class SqlPollReader
            rows.Add(row);
        }

+        if (plan.RowCap is { } rowCap && rows.Count > rowCap)
+        {
+            // Per plan, not reader-wide: with two ambiguous groups the reader-wide limiter could name only the
+            // first table forever, and with health still Healthy this line is the operator's only pointer.
+            if (ShouldWarn("rowcap:" + plan.SqlText))
+            {
+                var first = plan.Members[0];
+                var selector = plan.Model == SqlTagModel.KeyValue
+                    ? string.Concat(first.KeyColumn, " IN (", (rowCap / 2).ToString(CultureInfo.InvariantCulture), " key(s))")
+                    : string.Concat(first.RowSelectorColumn, " = ", first.RowSelectorValue);
+                _logger.LogWarning(
+                    "Sql poll source '{Table}' returned more rows than the {Model} selector '{Selector}' can attribute " +
+                    "(at most {Cap}) in one poll, so the selector is ambiguous — a history/events table, or a " +
+                    "where column that is not unique. Its {Members} tag(s) publish BadConfigurationError and " +
+                    "nothing past row {Limit} is read. Point the tag at a current-values table or a latest-row view.",
+                    first.Table, plan.Model, selector, rowCap, plan.Members.Count, rowCap + 1);
+            }
+
+            return GroupResult.RowCapExceeded;
+        }
+
        return GroupResult.Ok(rows, columnIndex, typeNames);
    }

@@ -470,8 +666,11 @@ public sealed class SqlPollReader
        }
    }

-    /// <summary>Maps one group's outcome onto every slot its members occupy in the caller's list.</summary>
-    private void Slice(
+    /// <summary>
+    ///     Maps one group's outcome onto every slot its members occupy in the caller's list. Returns whether any
+    ///     member was refused on an ANSWERED result (a duplicated key) — answer evidence the driver must count.
+    /// </summary>
+    private bool Slice(
        SqlQueryPlan plan,
        GroupResult outcome,
        Dictionary<SqlTagDefinition, List<int>> slots,
@@ -481,9 +680,11 @@ public sealed class SqlPollReader
        // KeyValue indexes rows by the key column; WideRow's members all read the one selected row, so the
        // where-column is not even in the result set (design §5.3). Both selections happen ONCE per group —
        // they are group-wide facts, and doing them per member would report a contract violation N times.
+        HashSet<string>? duplicatedKeys = null;
        var byKey = outcome.Succeeded && plan.Model == SqlTagModel.KeyValue
-            ? IndexByKey(plan, outcome)
+            ? IndexByKey(plan, outcome, out duplicatedKeys)
            : null;
+        var refusedSome = false;
        var wideRow = outcome.Succeeded && plan.Model == SqlTagModel.WideRow
            ? SelectWideRow(plan, outcome)
            : null;
@@ -493,26 +694,45 @@ public sealed class SqlPollReader
            // Members may repeat (two tags on one keyValue, or the same ref twice) — every occurrence is fed.
            if (!slots.TryGetValue(member, out var positions)) continue;

-            var snapshot = outcome.Succeeded
-                ? MapMember(plan, member, outcome, byKey, wideRow, readAt)
-                : new DataValueSnapshot(null, outcome.FailureStatus, null, readAt);
+            DataValueSnapshot snapshot;
+            if (!outcome.Succeeded)
+            {
+                snapshot = new DataValueSnapshot(null, outcome.FailureStatus, null, readAt);
+            }
+            else if (duplicatedKeys is not null && member.KeyValue is { } key && duplicatedKeys.Contains(key))
+            {
+                // More than one row for THIS tag's key: its selector is ambiguous — the same rule a where-pair
+                // follows — so it is a configuration error for this key's tags only. Every other key in the
+                // group is unaffected, whatever else is present or absent (R06:S-1 review I-1: it used to be
+                // last-row-wins Good, or the whole group Bad, depending on an unrelated key's absence).
+                snapshot = new DataValueSnapshot(null, SqlStatusCodes.BadConfigurationError, null, readAt);
+                refusedSome = true;
+            }
+            else
+            {
+                snapshot = MapMember(plan, member, outcome, byKey, wideRow, readAt);
+            }

            foreach (var position in positions) results[position] = snapshot;
        }
+
+        return refusedSome;
    }

    /// <summary>
-    ///     Builds the key → row index a key-value plan slices through. Later rows win, so a source that
-    ///     breaks the one-row-per-key contract (design §3.6) still yields a deterministic value; the
-    ///     violation is reported through a rate-limited warning rather than silently.
+    ///     Builds the key → row index a key-value plan slices through, and the set of keys that came back more
+    ///     than once — a source breaking the one-row-per-key contract (design §3.6). Those keys' tags publish
+    ///     <see cref="SqlStatusCodes.BadConfigurationError"/>; the violation is also reported through a
+    ///     per-plan rate-limited warning.
    /// </summary>
-    private Dictionary<string, object?[]> IndexByKey(SqlQueryPlan plan, GroupResult outcome)
+    private Dictionary<string, object?[]> IndexByKey(
+        SqlQueryPlan plan, GroupResult outcome, out HashSet<string>? duplicatedKeys)
    {
+        duplicatedKeys = null;
        var index = new Dictionary<string, object?[]>(StringComparer.Ordinal);
        if (plan.KeyColumn is null || !outcome.ColumnIndex.TryGetValue(plan.KeyColumn, out var keyAt))
            return index;

-        var duplicated = 0;
        foreach (var row in outcome.Rows)
        {
            // A NULL key cell indexes nothing: Convert.ToString would fold it to "", which would then be
@@ -523,20 +743,16 @@ public sealed class SqlPollReader
            // (an INTEGER station id, say) — the provider coerces on the way in, so match on the way out.
            var key = Convert.ToString(keyCell, CultureInfo.InvariantCulture);
            if (key is null) continue;
-            if (!index.TryAdd(key, row))
-            {
-                index[key] = row;
-                duplicated++;
-            }
+            if (!index.TryAdd(key, row)) (duplicatedKeys ??= new HashSet<string>(StringComparer.Ordinal)).Add(key);
        }

-        if (duplicated > 0 && ShouldWarnAboutContract())
+        if (duplicatedKeys is not null && ShouldWarn("dupkey:" + plan.SqlText))
        {
            _logger.LogWarning(
-                "Sql poll source '{Table}' returned more than one row for {Count} key(s) in one poll; the " +
-                "last row wins. The key-value model requires one row per key — point the tag at a " +
-                "current-values table or an operator-authored latest-per-key view.",
-                plan.Members[0].Table, duplicated);
+                "Sql poll source '{Table}' returned more than one row for {Count} key(s) in one poll (e.g. " +
+                "'{Example}'); those keys' tags publish BadConfigurationError. The key-value model requires one " +
+                "row per key — point the tag at a current-values table or an operator-authored latest-per-key view.",
+                plan.Members[0].Table, duplicatedKeys.Count, duplicatedKeys.First());
        }

        return index;
@@ -549,15 +765,14 @@ public sealed class SqlPollReader
    ///     emits no <c>ORDER BY</c>, so across polls the "last" row is whatever the server returned last,
    ///     i.e. storage order. That is why more than one row is a reported contract violation and not merely
    ///     a tie to break — the model's premise (design §5.3) is that the selector identifies one row.</para>
-    ///     <para><b>Why the where-pair form is deliberately NOT given the dialect's single-row limit.</b> A
-    ///     <c>TOP 1</c> with no <c>ORDER BY</c> is not deterministic either — it returns whichever row the
-    ///     plan happens to produce first, so it would trade one arbitrary row for a differently arbitrary
-    ///     one. Worse, it would destroy the only evidence this method has that the selector is ambiguous
-    ///     (<c>Rows.Count &gt; 1</c>), converting a loud misconfiguration into a permanently silent one —
-    ///     precisely the failure mode this class's summary calls its top risk. The <c>topByTimestamp</c>
-    ///     form keeps its row limit because there the <c>ORDER BY</c> at least fixes <em>which</em> rows can
-    ///     be first. The accepted cost is that an ambiguous selector materialises every matching row for one
-    ///     poll; the warning is what gets it fixed.</para>
+    ///     <para><b>Why the where-pair form is capped at TWO rows, not one (R06:S-1).</b> A <c>TOP 1</c> with no
+    ///     <c>ORDER BY</c> is not deterministic — it returns whichever row the plan produces first — and it would
+    ///     destroy the only evidence that the selector is ambiguous, converting a loud misconfiguration into a
+    ///     permanently silent one. No limit at all materialised every matching row of an events table on every
+    ///     poll. Two rows keeps the evidence and bounds the read: a second row makes the group publish
+    ///     <c>BadConfigurationError</c> in <c>MaterialiseAsync</c>, so a where-pair group never reaches this
+    ///     method with more than one row. The multi-row warning below is now reached only by a plan with no
+    ///     cap.</para>
    ///     <para><b>⚠ The <c>topByTimestamp</c> answer is only defined when the ordering column is unique</b>
    ///     <c>ORDER BY ts DESC</c> plus a one-row limit over a column with ties returns an
    ///     arbitrary row among the tied ones, and — unlike the where-pair form — this method can never
@@ -572,7 +787,7 @@ public sealed class SqlPollReader
    private object?[]? SelectWideRow(SqlQueryPlan plan, GroupResult outcome)
    {
        if (outcome.Rows.Count == 0) return null;
-        if (outcome.Rows.Count > 1 && ShouldWarnAboutContract())
+        if (outcome.Rows.Count > 1 && ShouldWarn("multirow:" + plan.SqlText))
        {
            var first = plan.Members[0];
            var selector = string.IsNullOrWhiteSpace(first.RowSelectorColumn)
@@ -642,9 +857,14 @@ public sealed class SqlPollReader
        var target = member.DeclaredType ?? _dialect.MapColumnType(outcome.TypeNames[valueAt]);
        if (!TryCoerce(cell, target, out var value))
        {
-            _logger.LogWarning(
-                "Sql tag '{Tag}' could not coerce a {Actual} cell to its {Declared} type.",
-                member.Name, cell.GetType().Name, target);
+            // A per-tag refusal: warned ONCE per tag (per reader), never per poll (R06:S-6).
+            if (_coerceWarned.TryAdd(member.Name, 0))
+            {
+                _logger.LogWarning(
+                    "Sql tag '{Tag}' could not coerce a {Actual} cell to its {Declared} type; it publishes " +
+                    "BadTypeMismatch (warned once per tag).",
+                    member.Name, cell.GetType().Name, target);
+            }
            return new DataValueSnapshot(null, SqlStatusCodes.BadTypeMismatch, sourceTimestamp, readAt);
        }

@@ -711,13 +931,21 @@ public sealed class SqlPollReader
            Convert.ToDateTime(cell, CultureInfo.InvariantCulture), DateTimeKind.Utc),
    };

-    /// <summary>Rate-limits the source-contract warning so a misconfigured table cannot flood the log.</summary>
-    private bool ShouldWarnAboutContract()
+    /// <summary>Rate-limits one per-poll warning by key; true at most once per <see cref="ContractWarningInterval"/>.</summary>
+    private bool ShouldWarn(string key)
    {
        var now = Stopwatch.GetTimestamp();
-        var last = Interlocked.Read(ref _lastContractWarningTicks);
-        if (last != 0 && Stopwatch.GetElapsedTime(last, now) < ContractWarningInterval) return false;
-        return Interlocked.CompareExchange(ref _lastContractWarningTicks, now, last) == last;
+        while (true)
+        {
+            if (!_lastWarnedTicks.TryGetValue(key, out var last))
+            {
+                if (_lastWarnedTicks.TryAdd(key, now)) return true;
+                continue;
+            }
+
+            if (Stopwatch.GetElapsedTime(last, now) < ContractWarningInterval) return false;
+            if (_lastWarnedTicks.TryUpdate(key, now, last)) return true;
+        }
    }

    /// <summary>One group's outcome: either a materialised result set, or the status its members inherit.</summary>
@@ -747,6 +975,17 @@ public sealed class SqlPollReader
        public static GroupResult Failed { get; } =
            new(SqlStatusCodes.BadCommunicationError, NoRows, NoColumns, []);

+        /// <summary>The reader was disposed before this group could start; surfaced as a typed exception.</summary>
+        public static GroupResult ReaderDisposed { get; } =
+            new(SqlStatusCodes.BadInternalError, NoRows, NoColumns, []);
+
+        /// <summary>
+        ///     The database answered with more rows than the plan can use — an ambiguous selector (R06:S-1).
+        ///     A configuration fact, not a database fault; the driver counts it as answer evidence.
+        /// </summary>
+        public static GroupResult RowCapExceeded { get; } =
+            new(SqlStatusCodes.BadConfigurationError, NoRows, NoColumns, []);
+
        /// <summary>The status every member inherits when <see cref="Succeeded"/> is false.</summary>
        public uint FailureStatus { get; }

@@ -775,6 +1014,21 @@ public sealed class SqlPollReader
    }
 }

+/// <summary>
+///     A poll reached a <see cref="SqlPollReader"/> after it was disposed — a rebind replaced it, or the driver
+///     was disposed. Not a database verdict: the driver retries on the current reader, and never degrades for it.
+/// </summary>
+public sealed class SqlPollReaderDisposedException()
+    : OperationCanceledException("The Sql poll reader was disposed (replaced by a rebind, or the driver was disposed).");
+
+/// <summary>One poll's snapshots plus the answer evidence they cannot carry themselves.</summary>
+/// <param name="Snapshots">One snapshot per requested reference, at the same index.</param>
+/// <param name="AnsweredRefusalGroups">
+///     Groups the database ANSWERED but whose result the reader refused in whole or part — an over-cap result
+///     set, or a duplicated key. Those members carry <see cref="SqlStatusCodes.BadConfigurationError"/>.
+/// </param>
+public sealed record SqlPollResult(IReadOnlyList<DataValueSnapshot> Snapshots, int AnsweredRefusalGroups);
+
 /// <summary>
 ///     The OPC UA status codes the Sql driver publishes, and the quality-class predicates its tests read
 ///     them back with.
@@ -55,6 +55,15 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Sql;
 ///     The bare (unquoted) column names in <see cref="SqlText"/>'s SELECT list, in order and distinct — the
 ///     reader's map from result-set ordinal to source column.
 /// </param>
+/// <param name="RowCap">
+///     The most rows the reader will attribute before refusing the whole group — twice the distinct key count
+///     (key-value: headroom so stray duplicates are attributed per key) or 1 (a where-pair wide row: one
+///     selector, so any second row is the group's ambiguity); <see langword="null"/> when the statement
+///     already limits itself (topByTimestamp). <see cref="SqlText"/> asks for <c>RowCap + 1</c>, and the
+///     reader stops there: receiving the extra row means a history/events table or a non-unique where column,
+///     and the group publishes <c>BadConfigurationError</c> instead of materialising every matching row on
+///     every poll (R06:S-1).
+/// </param>
 public sealed record SqlQueryPlan(
    SqlTagModel Model,
    object GroupKey,
@@ -63,7 +72,8 @@ public sealed record SqlQueryPlan(
    IReadOnlyList<string> ParameterBindNames,
    IReadOnlyList<object?> Parameters,
    IReadOnlyList<SqlTagDefinition> Members,
-    IReadOnlyList<string> SelectedColumns)
+    IReadOnlyList<string> SelectedColumns,
+    int? RowCap = null)
 {
    // A plan is documented as safe to cache and reuse across polls, so it must not stay aliased to the
    // planner's mutable working lists — an IReadOnlyList<T> holding a List<T> is downcastable, and a