diff --git a/docs/drivers/FOCAS.md b/docs/drivers/FOCAS.md
index 83504579..326c11ae 100644
--- a/docs/drivers/FOCAS.md
+++ b/docs/drivers/FOCAS.md
@@ -87,12 +87,33 @@ on.
 | `X0.0` / `R100` / `R100.3` | PMC bit or byte | Letter + number; optional `.bit` for bit access |
 | `PARAM:1815` / `PARAM:1815/0` | CNC parameter | Number + optional axis index |
 | `MACRO:500` | Custom macro variable | System / user macro variable number |
+| `FIXED:Identity/SeriesNumber` | Fixed-tree field | A path into the [fixed node tree](#fixed-node-tree) — read-only |
+
+The first three name a location the driver asks the CNC for on demand.
+`FIXED:` does not: it names a field of the per-device fixed-tree snapshot the
+driver's own poll loop already maintains, so a `FIXED:` read issues no wire
+traffic. It exists because the fixed tree is the only part of the FOCAS surface
+with no address of its own, and v3 publishes nodes only for authored tags — so
+without a form to author, the fixed tree could not be published at all.
+
+**An address never carries the device.** A tag's device comes from its raw-tag
+Device row; an address that also named a host would be a second, conflicting
+routing channel. This is worth stating because it is exactly what went wrong in
+[#540](https://gitea.dohertylan.com/dohertj2/lmxopcua/issues/540): browse leaves
+advertised `{deviceHost}/{path}` as their reference, the browse-commit wrote that
+into the address, and every committed tag read `BadNodeIdUnknown` forever.
 
 Addresses are validated against the per-device `Series` at `InitializeAsync` —
 a config referencing a number outside the documented range for that series
 fails at load time with an error message naming the limit. See
 [`docs/v2/focas-version-matrix.md`](../v2/focas-version-matrix.md) for the
-authoritative range table.
+authoritative range table. (`FIXED:` paths have no numeric range to check; a
+path the machine does not expose reads `BadNodeIdUnknown`.)
+
+An address the parser cannot read is rejected **when you author it** — by the
+`/raw` tag modal, and by the deploy-time inspector for config arriving via CSV
+import or the API. It is not a warning you can deploy past into a driver that
+skips the tag at startup.
 
 ## Backend selection
 
@@ -150,7 +171,34 @@ timers without declaring per-address tags.
 }
 ```
 
-What gets populated (all under `FOCAS/{deviceHostAddress}/`):
+`Enabled` defaults to **false** so an upgrade does not grow nodes on configs
+that never asked for them. You do not have to set it to use the tree: **authoring
+any `FIXED:` tag arms the poll loop by itself**, because committing those tags
+already says you want it. The flag remains the way to publish the tree without
+authoring anything (and the browser turns it on for the duration of a browse).
+
+### Authoring fixed-tree tags
+
+Browse the device (`/raw` → device → **Browse device…**, or the tag modal's
+**Browse machine**) and commit the leaves you want. Each leaf carries its own
+`FIXED:` address, so the commit produces working tags with no editing. The
+manual composer next to the browser covers PMC / `PARAM:` / `MACRO:` only —
+fixed-tree paths are discovered from the machine, not composed from parts.
+
+Two caveats worth knowing before you browse:
+
+- **A real CNC can report duplicate sibling names.** One observed Makino returns
+  two axis folders both called `AA`. Committing both is refused at commit time
+  (they would be the same RawPath), and the runtime cache is keyed by the same
+  name — so the `Axes/` subtree on such a machine cannot currently distinguish
+  them. Prefer the non-axis subtrees there until this is resolved.
+- **Values are dated from the last answered poll, not from the read.** If a CNC
+  stops answering, its fixed-tree values go `BadCommunicationError` rather than
+  continuing to serve the last snapshot as `Good`; the budget is eight poll
+  cadences, floored at 30 s.
+
+What gets populated (all under `FOCAS/{deviceHostAddress}/`, addressed as
+`FIXED:{subtree}/{field}`):
 
 | Subtree | Nodes | Source call |
 |---------|-------|-------------|
@@ -195,9 +243,9 @@ The driver now attempts to auto-scale each axis position using the CNC's `cnc_ge
 - No upper-bound clamp on the figure magnitude returned by the CNC — a misbehaving figure could overflow `Math.Pow`; a max-figure guard should be added.
 - The negative-figure branch (falls back to manual `PositionDecimalPlaces`) is handled but not explicitly unit-tested.
 
-**Still user-authored**: `PARAM:6711`, `MACRO:500`, `R100` etc. — specific
-numbers whose meaning is MTB-specific. Those go under the device folder
-alongside the fixed subtree.
+**Still hand-authored**: `PARAM:6711`, `MACRO:500`, `R100` etc. — specific
+numbers whose meaning is MTB-specific, and which no browse can discover. Those
+go under the device folder alongside the fixed subtree.
 
 ## Alarm projection
 
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Contracts/FocasAddress.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Contracts/FocasAddress.cs
new file mode 100644
index 00000000..862f7e10
--- /dev/null
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Contracts/FocasAddress.cs
@@ -0,0 +1,178 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+/// <summary>
+///     Parsed FOCAS address covering the four addressing spaces a driver touches:
+///     <see cref="FocasAreaKind.Pmc"/> (letter + byte + optional bit — <c>X0.0</c>, <c>R100</c>,
+///     <c>F20.3</c>), <see cref="FocasAreaKind.Parameter"/> (CNC parameter number —
+///     <c>PARAM:1020</c>, <c>PARAM:1815/0</c> for bit 0), <see cref="FocasAreaKind.Macro"/>
+///     (macro variable number — <c>MACRO:100</c>, <c>MACRO:500</c>), and
+///     <see cref="FocasAreaKind.Fixed"/> (a logical path into the driver's fixed tree —
+///     <c>FIXED:Identity/SeriesNumber</c>, <c>FIXED:Axes/X/AbsolutePosition</c>).
+/// </summary>
+/// <remarks>
+///     <para>PMC letters: <c>X/Y</c> (IO), <c>F/G</c> (signals between PMC + CNC), <c>R</c> (internal
+///     relay), <c>D</c> (data table), <c>C</c> (counter), <c>K</c> (keep relay), <c>A</c>
+///     (message display), <c>E</c> (extended relay), <c>T</c> (timer). Byte numbering is 0-based;
+///     bit index when present is 0–7 and uses <c>.N</c> for PMC or <c>/N</c> for parameters.</para>
+///     <para>
+///     <b><c>FIXED:</c> is not an area read.</b> The first three forms name a location the driver
+///     asks the CNC for on demand; a <c>FIXED:</c> path names a field of the per-device fixed-tree
+///     snapshot the driver's own poll loop already maintains (<c>cnc_sysinfo</c>, <c>cnc_rddynamic2</c>,
+///     program info, timers, spindle data). It exists because the fixed tree is the only part of the
+///     FOCAS surface with no address of its own, and v3 publishes nodes only for authored tags — so
+///     without a form to author, the fixed tree could not be published at all (Gitea #540).
+///     </para>
+///     <para>
+///     <b>The path carries no device.</b> A tag's device comes from its raw-tag Device row, and an
+///     address that also named a host would be a second, conflicting routing channel — which is
+///     precisely the defect #540 reported: the browse leaf's <c>{host}/{path}</c> full reference was
+///     written into the address field verbatim and then failed to parse, so every browse-committed
+///     fixed-tree tag read <c>BadNodeIdUnknown</c> forever.
+///     </para>
+/// </remarks>
+public sealed record FocasAddress(
+    FocasAreaKind Kind,
+    string? PmcLetter,
+    int Number,
+    int? BitIndex,
+    string? FixedPath = null)
+{
+    /// <summary>The prefix that introduces a <see cref="FocasAreaKind.Fixed"/> address.</summary>
+    public const string FixedPrefix = "FIXED:";
+
+    /// <summary>Gets the canonical string representation of this address.</summary>
+    public string Canonical => Kind switch
+    {
+        FocasAreaKind.Pmc => BitIndex is null
+            ? $"{PmcLetter}{Number}"
+            : $"{PmcLetter}{Number}.{BitIndex}",
+        FocasAreaKind.Parameter => BitIndex is null
+            ? $"PARAM:{Number}"
+            : $"PARAM:{Number}/{BitIndex}",
+        FocasAreaKind.Macro => $"MACRO:{Number}",
+        FocasAreaKind.Fixed => FixedPrefix + FixedPath,
+        _ => $"?{Number}",
+    };
+
+    /// <summary>
+    ///     Builds the canonical authored address for a fixed-tree path. The one place the
+    ///     <c>FIXED:</c> spelling is constructed, so the browse emitter and the parser cannot drift.
+    /// </summary>
+    /// <param name="path">The fixed-tree path, e.g. <c>Identity/SeriesNumber</c>.</param>
+    /// <returns>The canonical authored address string.</returns>
+    public static string ForFixedPath(string path) => FixedPrefix + path;
+
+    /// <summary>Attempts to parse a FOCAS address from the given string.</summary>
+    /// <param name="value">The address string to parse.</param>
+    /// <returns>A FocasAddress if parsing succeeds; otherwise null.</returns>
+    public static FocasAddress? TryParse(string? value)
+    {
+        if (string.IsNullOrWhiteSpace(value)) return null;
+        var src = value.Trim();
+
+        if (src.StartsWith("PARAM:", StringComparison.OrdinalIgnoreCase))
+            return ParseScoped(src["PARAM:".Length..], FocasAreaKind.Parameter, bitSeparator: '/');
+
+        if (src.StartsWith("MACRO:", StringComparison.OrdinalIgnoreCase))
+            return ParseScoped(src["MACRO:".Length..], FocasAreaKind.Macro, bitSeparator: null);
+
+        // Fixed-tree path. Tested BEFORE the PMC branch on purpose: "F" is a valid PMC letter, so a
+        // FIXED: address entering that branch would be diagnosed as a malformed PMC address rather
+        // than as the fixed-tree address it is. (It would still return null either way — this is
+        // about which rule owns the string, not about the result.)
+        if (src.StartsWith(FixedPrefix, StringComparison.OrdinalIgnoreCase))
+        {
+            var path = NormalizeFixedPath(src[FixedPrefix.Length..]);
+            return path is null ? null : new FocasAddress(FocasAreaKind.Fixed, null, 0, null, path);
+        }
+
+        // PMC path: letter + digits + optional .bit
+        if (src.Length < 2 || !char.IsLetter(src[0])) return null;
+        var letter = src[0..1].ToUpperInvariant();
+        if (!IsValidPmcLetter(letter)) return null;
+
+        var remainder = src[1..];
+        int? bit = null;
+        var dotIdx = remainder.IndexOf('.');
+        if (dotIdx >= 0)
+        {
+            if (!int.TryParse(remainder[(dotIdx + 1)..], out var bitValue) || bitValue is < 0 or > 7)
+                return null;
+            bit = bitValue;
+            remainder = remainder[..dotIdx];
+        }
+        if (!int.TryParse(remainder, out var number) || number < 0) return null;
+        return new FocasAddress(FocasAreaKind.Pmc, letter, number, bit);
+    }
+
+    private static FocasAddress? ParseScoped(string body, FocasAreaKind kind, char? bitSeparator)
+    {
+        int? bit = null;
+        if (bitSeparator is char sep)
+        {
+            var slashIdx = body.IndexOf(sep);
+            if (slashIdx >= 0)
+            {
+                if (!int.TryParse(body[(slashIdx + 1)..], out var bitValue) || bitValue is < 0 or > 31)
+                    return null;
+                bit = bitValue;
+                body = body[..slashIdx];
+            }
+        }
+        if (!int.TryParse(body, out var number) || number < 0) return null;
+        return new FocasAddress(kind, PmcLetter: null, number, bit);
+    }
+
+    /// <summary>
+    ///     Validates a fixed-tree path and returns it, or null when it is not a usable path.
+    ///     Accepts <c>Segment[/Segment…]</c> where each segment is non-blank and carries no
+    ///     <c>:</c> — a colon would collide with the <c>PARAM:</c>/<c>MACRO:</c>/<c>FIXED:</c>
+    ///     prefix grammar and make the address ambiguous to read back.
+    /// </summary>
+    /// <remarks>
+    ///     Deliberately shape-only: it does NOT check the path against the fixed tree a particular
+    ///     CNC actually exposes. What that tree contains is per-device and discovered at runtime
+    ///     (spindles, program info and timers are each capability-gated), so a parser that judged
+    ///     membership would have to reject addresses that are valid on the machine they were
+    ///     authored against. An unknown path resolves to no value at read time, which is where the
+    ///     device is known.
+    /// </remarks>
+    private static string? NormalizeFixedPath(string body)
+    {
+        var path = body.Trim();
+        if (path.Length == 0) return null;
+        if (path.Contains(':', StringComparison.Ordinal)) return null;
+        if (path[0] == '/' || path[^1] == '/') return null;
+
+        foreach (var segment in path.Split('/'))
+            if (string.IsNullOrWhiteSpace(segment)) return null;
+
+        return path;
+    }
+
+    private static bool IsValidPmcLetter(string letter) => letter switch
+    {
+        "X" or "Y" or "F" or "G" or "R" or "D" or "C" or "K" or "A" or "E" or "T" => true,
+        _ => false,
+    };
+}
+
+/// <summary>Addressing-space kinds the driver understands.</summary>
+public enum FocasAreaKind
+{
+    /// <summary>PMC area — letter + byte + optional bit (<c>X0.0</c>, <c>R100</c>).</summary>
+    Pmc,
+
+    /// <summary>CNC parameter number (<c>PARAM:1020</c>, <c>PARAM:1815/0</c>).</summary>
+    Parameter,
+
+    /// <summary>Macro variable number (<c>MACRO:100</c>).</summary>
+    Macro,
+
+    /// <summary>
+    ///     A logical path into the driver's per-device fixed tree (<c>FIXED:Identity/SeriesNumber</c>).
+    ///     Served from the fixed-tree poll snapshot, never from an area read — and read-only, because
+    ///     nothing in that tree is a writable location on the CNC.
+    /// </summary>
+    Fixed,
+}
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Contracts/FocasTagDefinitionFactory.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Contracts/FocasTagDefinitionFactory.cs
index 7bef3447..3ece4da2 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Contracts/FocasTagDefinitionFactory.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Contracts/FocasTagDefinitionFactory.cs
@@ -117,6 +117,21 @@ public static class FocasTagDefinitionFactory
             }
             var w = TagConfigJson.DescribeInvalidEnum<FocasDataType>(root, "dataType");
             if (w is not null) warnings.Add(w);
+            // Gitea #540: an address the driver cannot parse is skipped at init and reads
+            // BadNodeIdUnknown forever, while driver health stays Healthy with zero errors. The
+            // AdminUI modal rejects it outright; this covers the paths that never touch the modal
+            // (CSV import, the API) by at least surfacing it on the deployment.
+            if (root.TryGetProperty("address", out var addr)
+                && addr.ValueKind == JsonValueKind.String
+                && addr.GetString() is { } address
+                && !string.IsNullOrWhiteSpace(address)
+                && FocasAddress.TryParse(address) is null)
+            {
+                warnings.Add(
+                    $"FOCAS address '{address.Trim()}' is not parseable (expected X0.0 / R100, " +
+                    "PARAM:1020, MACRO:500 or FIXED:Identity/SeriesNumber) — the driver will skip " +
+                    "this tag at startup and it will read BadNodeIdUnknown.");
+            }
             if (root.TryGetProperty("writable", out var wr) && wr.ValueKind == JsonValueKind.True)
                 warnings.Add("FOCAS wire is read-only — an authored 'writable:true' still fails at the wire with BadNotWritable.");
         }
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasAddress.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasAddress.cs
deleted file mode 100644
index df4434f0..00000000
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasAddress.cs
+++ /dev/null
@@ -1,99 +0,0 @@
-namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
-
-/// <summary>
-///     Parsed FOCAS address covering the three addressing spaces a driver touches:
-///     <see cref="FocasAreaKind.Pmc"/> (letter + byte + optional bit — <c>X0.0</c>, <c>R100</c>,
-///     <c>F20.3</c>), <see cref="FocasAreaKind.Parameter"/> (CNC parameter number —
-///     <c>PARAM:1020</c>, <c>PARAM:1815/0</c> for bit 0), and <see cref="FocasAreaKind.Macro"/>
-///     (macro variable number — <c>MACRO:100</c>, <c>MACRO:500</c>).
-/// </summary>
-/// <remarks>
-///     PMC letters: <c>X/Y</c> (IO), <c>F/G</c> (signals between PMC + CNC), <c>R</c> (internal
-///     relay), <c>D</c> (data table), <c>C</c> (counter), <c>K</c> (keep relay), <c>A</c>
-///     (message display), <c>E</c> (extended relay), <c>T</c> (timer). Byte numbering is 0-based;
-///     bit index when present is 0–7 and uses <c>.N</c> for PMC or <c>/N</c> for parameters.
-/// </remarks>
-public sealed record FocasAddress(
-    FocasAreaKind Kind,
-    string? PmcLetter,
-    int Number,
-    int? BitIndex)
-{
-    /// <summary>Gets the canonical string representation of this address.</summary>
-    public string Canonical => Kind switch
-    {
-        FocasAreaKind.Pmc => BitIndex is null
-            ? $"{PmcLetter}{Number}"
-            : $"{PmcLetter}{Number}.{BitIndex}",
-        FocasAreaKind.Parameter => BitIndex is null
-            ? $"PARAM:{Number}"
-            : $"PARAM:{Number}/{BitIndex}",
-        FocasAreaKind.Macro => $"MACRO:{Number}",
-        _ => $"?{Number}",
-    };
-
-    /// <summary>Attempts to parse a FOCAS address from the given string.</summary>
-    /// <param name="value">The address string to parse.</param>
-    /// <returns>A FocasAddress if parsing succeeds; otherwise null.</returns>
-    public static FocasAddress? TryParse(string? value)
-    {
-        if (string.IsNullOrWhiteSpace(value)) return null;
-        var src = value.Trim();
-
-        if (src.StartsWith("PARAM:", StringComparison.OrdinalIgnoreCase))
-            return ParseScoped(src["PARAM:".Length..], FocasAreaKind.Parameter, bitSeparator: '/');
-
-        if (src.StartsWith("MACRO:", StringComparison.OrdinalIgnoreCase))
-            return ParseScoped(src["MACRO:".Length..], FocasAreaKind.Macro, bitSeparator: null);
-
-        // PMC path: letter + digits + optional .bit
-        if (src.Length < 2 || !char.IsLetter(src[0])) return null;
-        var letter = src[0..1].ToUpperInvariant();
-        if (!IsValidPmcLetter(letter)) return null;
-
-        var remainder = src[1..];
-        int? bit = null;
-        var dotIdx = remainder.IndexOf('.');
-        if (dotIdx >= 0)
-        {
-            if (!int.TryParse(remainder[(dotIdx + 1)..], out var bitValue) || bitValue is < 0 or > 7)
-                return null;
-            bit = bitValue;
-            remainder = remainder[..dotIdx];
-        }
-        if (!int.TryParse(remainder, out var number) || number < 0) return null;
-        return new FocasAddress(FocasAreaKind.Pmc, letter, number, bit);
-    }
-
-    private static FocasAddress? ParseScoped(string body, FocasAreaKind kind, char? bitSeparator)
-    {
-        int? bit = null;
-        if (bitSeparator is char sep)
-        {
-            var slashIdx = body.IndexOf(sep);
-            if (slashIdx >= 0)
-            {
-                if (!int.TryParse(body[(slashIdx + 1)..], out var bitValue) || bitValue is < 0 or > 31)
-                    return null;
-                bit = bitValue;
-                body = body[..slashIdx];
-            }
-        }
-        if (!int.TryParse(body, out var number) || number < 0) return null;
-        return new FocasAddress(kind, PmcLetter: null, number, bit);
-    }
-
-    private static bool IsValidPmcLetter(string letter) => letter switch
-    {
-        "X" or "Y" or "F" or "G" or "R" or "D" or "C" or "K" or "A" or "E" or "T" => true,
-        _ => false,
-    };
-}
-
-/// <summary>Addressing-space kinds the driver understands.</summary>
-public enum FocasAreaKind
-{
-    Pmc,
-    Parameter,
-    Macro,
-}
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasCapabilityMatrix.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasCapabilityMatrix.cs
index 4d11dff8..b8037e54 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasCapabilityMatrix.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasCapabilityMatrix.cs
@@ -1,7 +1,7 @@
 namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
 
 /// <summary>
-///     Documented-API capability matrix — per CNC series, what ranges each
+///     Documented-API capability matrix — per CNC series, what ranges each addressed
 ///     <see cref="FocasAreaKind"/> supports. Authoritative source for the driver's
 ///     pre-flight validation in <see cref="FocasDriver.InitializeAsync"/>.
 /// </summary>
@@ -35,6 +35,10 @@ public static class FocasCapabilityMatrix
             FocasAreaKind.Macro     => ValidateMacro(series, address.Number),
             FocasAreaKind.Parameter => ValidateParameter(series, address.Number),
             FocasAreaKind.Pmc       => ValidatePmc(series, address.PmcLetter, address.Number),
+            // Fixed-tree paths are not area reads, so there is no per-series numeric range to check.
+            // What a given CNC actually exposes there is discovered at runtime and capability-gated
+            // per subtree; a path this machine does not have resolves to BadNodeIdUnknown at read.
+            FocasAreaKind.Fixed     => null,
             _ => null,
         };
     }
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasDriver.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasDriver.cs
index aea048ff..898d5a6d 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasDriver.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasDriver.cs
@@ -49,6 +49,21 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
     // produced equipment tags are encountered for the first time.
     private readonly ConcurrentDictionary<string, FocasAddress> _parsedAddressesByTagName =
         new(StringComparer.OrdinalIgnoreCase);
+    /// <summary>
+    ///     Whether this driver instance runs its per-device fixed-tree poll loop, and therefore
+    ///     serves fixed-tree values. Computed at <see cref="InitializeAsync"/> from the config flag
+    ///     OR the presence of at least one authored <see cref="FocasAreaKind.Fixed"/> tag.
+    /// </summary>
+    /// <remarks>
+    ///     <b>The OR is load-bearing.</b> <c>FocasFixedTreeOptions.Enabled</c> defaults to
+    ///     <see langword="false"/> so an upgrade does not grow nodes on configs that never asked for
+    ///     them, and the universal browser force-enables it for the duration of a browse only. An
+    ///     operator therefore browses the fixed tree, commits leaves from it, deploys — and lands on
+    ///     a driver whose loop never starts, so every one of those tags reads Bad with a correct
+    ///     address. Authoring a <c>FIXED:</c> tag IS the request for the tree; the config flag stays
+    ///     as the way to publish it without authoring anything.
+    /// </remarks>
+    private bool _fixedTreeActive;
     private FocasAlarmProjection? _alarmProjection;
     // _health is read/written from multiple threads (ReadAsync, WriteAsync, ProbeLoopAsync).
     // Volatile.Read/Write ensures every thread sees the latest reference without a lock — the
@@ -248,7 +263,12 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
             if (_options.AlarmProjection.Enabled)
                 _alarmProjection = new FocasAlarmProjection(this, _options.AlarmProjection.PollInterval, _logger);
 
-            if (_options.FixedTree.Enabled)
+            // See _fixedTreeActive: an authored FIXED: tag arms the loop on its own, because the
+            // config flag defaults off and the operator who committed those tags has already said
+            // what they want.
+            _fixedTreeActive = _options.FixedTree.Enabled
+                || _parsedAddressesByTagName.Values.Any(a => a.Kind == FocasAreaKind.Fixed);
+            if (_fixedTreeActive)
             {
                 foreach (var state in _devices.Values)
                 {
@@ -306,6 +326,7 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
         _tagsByRawPath.Clear();
         _resolver.Clear(); // no-op in v3 (the resolver reads the live table by closure); kept for symmetry
         _parsedAddressesByTagName.Clear();
+        _fixedTreeActive = false;
         Volatile.Write(ref _health, new DriverHealth(DriverState.Unknown, Volatile.Read(ref _health).LastSuccessfulRead, null));
     }
 
@@ -377,7 +398,11 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
             // Fixed-tree T1 — fixed-tree references are synthesized from the cached
             // dynamic snapshot + sysinfo; no P/Invoke per Read since the poll loop
             // already fires them on cadence.
-            if (_options.FixedTree.Enabled && TryReadFixedTree(reference, now) is { } fx)
+            //
+            // This branch matches a reference that IS a "{host}/{path}" fixed-tree key. Authored
+            // tags do not take it — their reference is a RawPath — and are served further down by
+            // their FIXED: address instead (Gitea #540).
+            if (_fixedTreeActive && TryReadFixedTree(reference, now) is { } fx)
             {
                 results[i] = fx;
                 continue;
@@ -396,8 +421,28 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
 
             try
             {
-                var client = await EnsureConnectedAsync(device, cancellationToken).ConfigureAwait(false);
                 var parsed = ResolveParsedAddress(def);
+
+                // A FIXED: tag names a field of this device's fixed-tree snapshot, which the
+                // fixed-tree loop already maintains — there is no area read to issue, and no
+                // connection to force. A null here means the path resolves to nothing on THIS
+                // device (an unsupported capability, a renamed axis, a typo), which is a genuine
+                // BadNodeIdUnknown; a device that has not answered yet reports a comms fault
+                // instead, because the address may well be fine.
+                if (parsed.Kind == FocasAreaKind.Fixed)
+                {
+                    results[i] = TryReadFixedTreeOnDevice(device, parsed.FixedPath!, now)
+                        ?? new DataValueSnapshot(
+                            null,
+                            device.LastFixedPollUtc is null
+                                ? FocasStatusMapper.BadCommunicationError
+                                : FocasStatusMapper.BadNodeIdUnknown,
+                            null,
+                            now);
+                    continue;
+                }
+
+                var client = await EnsureConnectedAsync(device, cancellationToken).ConfigureAwait(false);
                 var (value, status) = await client.ReadAsync(parsed, def.DataType, cancellationToken).ConfigureAwait(false);
 
                 results[i] = new DataValueSnapshot(value, status, now, now);
@@ -459,8 +504,18 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
 
             try
             {
-                var client = await EnsureConnectedAsync(device, cancellationToken).ConfigureAwait(false);
                 var parsed = ResolveParsedAddress(def);
+
+                // Nothing in the fixed tree is a writable location on the CNC — it is a read-out of
+                // machine state (identity, positions, program, timers). Refuse before opening a
+                // connection rather than sending a write the wire would reject anyway.
+                if (parsed.Kind == FocasAreaKind.Fixed)
+                {
+                    results[i] = new WriteResult(FocasStatusMapper.BadNotWritable);
+                    continue;
+                }
+
+                var client = await EnsureConnectedAsync(device, cancellationToken).ConfigureAwait(false);
                 var status = await client.WriteAsync(parsed, def.DataType, w.Value, cancellationToken).ConfigureAwait(false);
                 results[i] = new WriteResult(status);
             }
@@ -525,31 +580,31 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
 
             // Fixed-tree T1 — Identity + Axes subtrees, populated once per session
             // from cnc_sysinfo + cnc_rdaxisname at init time and kept in DeviceState.
-            if (_options.FixedTree.Enabled
+            if (_fixedTreeActive
                 && _devices.TryGetValue(device.HostAddress, out var state)
                 && state.FixedTreeCache is { } cache)
             {
                 var identity = deviceFolder.Folder("Identity", "Identity");
-                EmitIdentityVariable(identity, device.HostAddress, "SeriesNumber", FocasDriverDataType.String);
-                EmitIdentityVariable(identity, device.HostAddress, "Version", FocasDriverDataType.String);
-                EmitIdentityVariable(identity, device.HostAddress, "MaxAxes", FocasDriverDataType.Int32);
-                EmitIdentityVariable(identity, device.HostAddress, "CncType", FocasDriverDataType.String);
-                EmitIdentityVariable(identity, device.HostAddress, "MtType", FocasDriverDataType.String);
-                EmitIdentityVariable(identity, device.HostAddress, "AxisCount", FocasDriverDataType.Int32);
+                EmitIdentityVariable(identity, "SeriesNumber", FocasDriverDataType.String);
+                EmitIdentityVariable(identity, "Version", FocasDriverDataType.String);
+                EmitIdentityVariable(identity, "MaxAxes", FocasDriverDataType.Int32);
+                EmitIdentityVariable(identity, "CncType", FocasDriverDataType.String);
+                EmitIdentityVariable(identity, "MtType", FocasDriverDataType.String);
+                EmitIdentityVariable(identity, "AxisCount", FocasDriverDataType.Int32);
 
                 var axesFolder = deviceFolder.Folder("Axes", "Axes");
                 foreach (var axis in cache.Axes)
                 {
                     var axisFolder = axesFolder.Folder(axis.Display, axis.Display);
-                    EmitAxisVariable(axisFolder, device.HostAddress, axis.Display, "AbsolutePosition");
-                    EmitAxisVariable(axisFolder, device.HostAddress, axis.Display, "MachinePosition");
-                    EmitAxisVariable(axisFolder, device.HostAddress, axis.Display, "RelativePosition");
-                    EmitAxisVariable(axisFolder, device.HostAddress, axis.Display, "DistanceToGo");
+                    EmitAxisVariable(axisFolder, axis.Display, "AbsolutePosition");
+                    EmitAxisVariable(axisFolder, axis.Display, "MachinePosition");
+                    EmitAxisVariable(axisFolder, axis.Display, "RelativePosition");
+                    EmitAxisVariable(axisFolder, axis.Display, "DistanceToGo");
                     if (cache.Capabilities.ServoLoad)
-                        EmitAxisVariable(axisFolder, device.HostAddress, axis.Display, "ServoLoad");
+                        EmitAxisVariable(axisFolder, axis.Display, "ServoLoad");
                 }
-                EmitAxisVariable(axesFolder, device.HostAddress, "FeedRate", "Actual");
-                EmitAxisVariable(axesFolder, device.HostAddress, "SpindleSpeed", "Actual");
+                EmitAxisVariable(axesFolder, "FeedRate", "Actual");
+                EmitAxisVariable(axesFolder, "SpindleSpeed", "Actual");
 
                 // Spindle subtree — one folder per discovered spindle, suppressed
                 // entirely on series that don't export cnc_rdspdlname. Per-spindle
@@ -563,9 +618,9 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
                         var name = string.IsNullOrEmpty(s.Display) ? $"S{i + 1}" : s.Display;
                         var spindleFolder = spindleRoot.Folder(name, name);
                         if (cache.Capabilities.SpindleLoad)
-                            EmitFixedVariable(spindleFolder, device.HostAddress, $"Spindle/{name}", "Load", DriverDataType.Int32);
+                            EmitFixedVariable(spindleFolder, $"Spindle/{name}", "Load", DriverDataType.Int32);
                         if (cache.Capabilities.SpindleMaxRpm && i < cache.SpindleMaxRpms.Count)
-                            EmitFixedVariable(spindleFolder, device.HostAddress, $"Spindle/{name}", "MaxRpm", DriverDataType.Int32);
+                            EmitFixedVariable(spindleFolder, $"Spindle/{name}", "MaxRpm", DriverDataType.Int32);
                     }
                 }
 
@@ -573,26 +628,26 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
                 if (cache.Capabilities.ProgramInfo)
                 {
                     var program = deviceFolder.Folder("Program", "Program");
-                    EmitFixedVariable(program, device.HostAddress, "Program", "Name", DriverDataType.String);
-                    EmitFixedVariable(program, device.HostAddress, "Program", "ONumber", DriverDataType.Int32);
-                    EmitFixedVariable(program, device.HostAddress, "Program", "Number", DriverDataType.Int32);
-                    EmitFixedVariable(program, device.HostAddress, "Program", "MainNumber", DriverDataType.Int32);
-                    EmitFixedVariable(program, device.HostAddress, "Program", "Sequence", DriverDataType.Int32);
-                    EmitFixedVariable(program, device.HostAddress, "Program", "BlockCount", DriverDataType.Int32);
+                    EmitFixedVariable(program, "Program", "Name", DriverDataType.String);
+                    EmitFixedVariable(program, "Program", "ONumber", DriverDataType.Int32);
+                    EmitFixedVariable(program, "Program", "Number", DriverDataType.Int32);
+                    EmitFixedVariable(program, "Program", "MainNumber", DriverDataType.Int32);
+                    EmitFixedVariable(program, "Program", "Sequence", DriverDataType.Int32);
+                    EmitFixedVariable(program, "Program", "BlockCount", DriverDataType.Int32);
 
                     var opMode = deviceFolder.Folder("OperationMode", "OperationMode");
-                    EmitFixedVariable(opMode, device.HostAddress, "OperationMode", "Mode", DriverDataType.Int32);
-                    EmitFixedVariable(opMode, device.HostAddress, "OperationMode", "ModeText", DriverDataType.String);
+                    EmitFixedVariable(opMode, "OperationMode", "Mode", DriverDataType.Int32);
+                    EmitFixedVariable(opMode, "OperationMode", "ModeText", DriverDataType.String);
                 }
 
                 // Fixed-tree T3 — Timers subtree (power-on / operating / cutting / cycle).
                 if (cache.Capabilities.Timers)
                 {
                     var timers = deviceFolder.Folder("Timers", "Timers");
-                    EmitFixedVariable(timers, device.HostAddress, "Timers", "PowerOnSeconds", DriverDataType.Float64);
-                    EmitFixedVariable(timers, device.HostAddress, "Timers", "OperatingSeconds", DriverDataType.Float64);
-                    EmitFixedVariable(timers, device.HostAddress, "Timers", "CuttingSeconds", DriverDataType.Float64);
-                    EmitFixedVariable(timers, device.HostAddress, "Timers", "CycleSeconds", DriverDataType.Float64);
+                    EmitFixedVariable(timers, "Timers", "PowerOnSeconds", DriverDataType.Float64);
+                    EmitFixedVariable(timers, "Timers", "OperatingSeconds", DriverDataType.Float64);
+                    EmitFixedVariable(timers, "Timers", "CuttingSeconds", DriverDataType.Float64);
+                    EmitFixedVariable(timers, "Timers", "CycleSeconds", DriverDataType.Float64);
                 }
             }
 
@@ -622,10 +677,33 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
 
     private enum FocasDriverDataType { String, Int32, Float64 }
 
+    /// <summary>
+    ///     Emit one <c>Identity</c> leaf.
+    /// </summary>
+    /// <remarks>
+    ///     <para>
+    ///     <b>The emitted <c>FullName</c> is the authorable address, not the runtime cache key.</b>
+    ///     A captured browse leaf's id IS its <c>FullName</c>, and that string is what both the
+    ///     <c>/raw</c> browse-commit mapper and the manual picker's tree-select write into the tag's
+    ///     <c>TagConfig.address</c>. Emitting the host-prefixed cache key therefore authored an
+    ///     address no FOCAS parser accepts: the driver skipped every such tag at init and each one
+    ///     read <c>BadNodeIdUnknown</c> forever, while the deploy sealed green and driver health
+    ///     stayed Healthy (Gitea #540).
+    ///     </para>
+    ///     <para>
+    ///     The host is dropped rather than stripped later because a tag's device is already carried
+    ///     by its raw-tag Device row. Two routing channels for one fact is what created the defect;
+    ///     one channel is the fix. <see cref="FixedTreeReference"/> keeps the host for the internal
+    ///     per-device caches, which do need to distinguish devices.
+    ///     </para>
+    /// </remarks>
+    /// <param name="folder">The address-space folder to emit into.</param>
+    /// <param name="field">The identity field name.</param>
+    /// <param name="type">The field's data type.</param>
     private static void EmitIdentityVariable(
-        IAddressSpaceBuilder folder, string deviceHost, string field, FocasDriverDataType type)
+        IAddressSpaceBuilder folder, string field, FocasDriverDataType type)
     {
-        var fullName = FixedTreeReference(deviceHost, $"Identity/{field}");
+        var fullName = FocasAddress.ForFixedPath($"Identity/{field}");
         folder.Variable(field, field, new DriverAttributeInfo(
             FullName: fullName,
             DriverDataType: type switch
@@ -643,10 +721,14 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
             NativeDataType: NativeName(type)));
     }
 
+    /// <summary>Emit one <c>Axes</c> leaf. See <see cref="EmitIdentityVariable"/> on the address shape.</summary>
+    /// <param name="folder">The address-space folder to emit into.</param>
+    /// <param name="axisName">The axis display name.</param>
+    /// <param name="field">The per-axis field name.</param>
     private static void EmitAxisVariable(
-        IAddressSpaceBuilder folder, string deviceHost, string axisName, string field)
+        IAddressSpaceBuilder folder, string axisName, string field)
     {
-        var fullName = FixedTreeReference(deviceHost, $"Axes/{axisName}/{field}");
+        var fullName = FocasAddress.ForFixedPath($"Axes/{axisName}/{field}");
         folder.Variable(field, field, new DriverAttributeInfo(
             FullName: fullName,
             DriverDataType: DriverDataType.Float64,
@@ -675,13 +757,17 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
 
     /// <summary>
     ///     Emit a variable under a named fixed-tree folder (Program, OperationMode,
-    ///     …). Full-reference shape is <c>{deviceHost}/{folderPath}/{field}</c>.
+    ///     …). Address shape is <c>FIXED:{folderPath}/{field}</c> — see
+    ///     <see cref="EmitIdentityVariable"/>.
     /// </summary>
+    /// <param name="folder">The address-space folder to emit into.</param>
+    /// <param name="folderPath">The fixed-tree folder path.</param>
+    /// <param name="field">The field name.</param>
+    /// <param name="type">The field's data type.</param>
     private static void EmitFixedVariable(
-        IAddressSpaceBuilder folder, string deviceHost, string folderPath,
-        string field, DriverDataType type)
+        IAddressSpaceBuilder folder, string folderPath, string field, DriverDataType type)
     {
-        var fullName = FixedTreeReference(deviceHost, $"{folderPath}/{field}");
+        var fullName = FocasAddress.ForFixedPath($"{folderPath}/{field}");
         folder.Variable(field, field, new DriverAttributeInfo(
             FullName: fullName,
             DriverDataType: type,
@@ -700,14 +786,19 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
     }
 
     /// <summary>
-    ///     Canonical full-reference shape for a fixed-tree node. Keeps the device
+    ///     Canonical <b>runtime cache key</b> for a fixed-tree node. Keeps the device
     ///     host as a prefix so multi-device configs don't collide, and the rest is
     ///     the path inside the tree. Matches what poll-loop snapshots publish +
-    ///     what <see cref="ReadAsync"/> looks up.
+    ///     what <see cref="TryReadFixedTreeOnDevice"/> looks up.
     /// </summary>
+    /// <remarks>
+    ///     <b>This is an internal key, not an authorable address</b> — see
+    ///     <see cref="EmitIdentityVariable"/> for why the two are deliberately different strings
+    ///     (Gitea #540).
+    /// </remarks>
     /// <param name="deviceHost">The host address of the device.</param>
     /// <param name="path">The path within the fixed tree.</param>
-    /// <returns>The canonical full reference for the node.</returns>
+    /// <returns>The canonical cache key for the node.</returns>
     internal static string FixedTreeReference(string deviceHost, string path) =>
         $"{deviceHost}/{path}";
 
@@ -823,6 +914,10 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
 
                 state.FixedTreeCache = new FocasFixedTreeCache(
                     sys, [.. axes], [.. spindles], [.. spindleMaxRpms], caps);
+                // The bootstrap IS an answer from the device, and Identity comes entirely from it —
+                // so stamp liveness here as well as per tick, or a CNC whose axis poll never
+                // succeeds would serve a perfectly valid sysinfo as stale.
+                state.LastFixedPollUtc = DateTime.UtcNow;
             }
             catch (OperationCanceledException) when (ct.IsCancellationRequested) { return; }
             catch (Exception ex)
@@ -872,6 +967,11 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
                     if (i == 0) { firstAxisSnap = snap; PublishRateSnapshot(state, snap); }
                 }
 
+                // The device answered this tick. Stamped after the axis pass rather than at the top
+                // of the loop: EnsureConnectedAsync can hand back a cached handle without any wire
+                // traffic, so it alone does not prove the CNC is still there.
+                state.LastFixedPollUtc = DateTime.UtcNow;
+
                 // Servo loads + spindle loads — both return bulk arrays, so folding
                 // into the axis cadence is cheap. Each is gated by the bootstrap
                 // capability probe — unsupported on this series = silent skip.
@@ -1054,79 +1154,119 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
         foreach (var state in _devices.Values)
         {
             if (!reference.StartsWith(state.Options.HostAddress + "/", StringComparison.OrdinalIgnoreCase)) continue;
-            if (state.LastFixedSnapshots.TryGetValue(reference, out var raw))
-                return new DataValueSnapshot(raw, FocasStatusMapper.Good, now, now);
+            if (TryReadFixedTreeOnDevice(state, reference[(state.Options.HostAddress.Length + 1)..], now) is { } hit)
+                return hit;
+        }
+        return null;
+    }
 
-            // Servo-load match: reference shape is "{host}/Axes/{name}/ServoLoad"
-            var suffixFull = reference[(state.Options.HostAddress.Length + 1)..];
-            if (suffixFull.StartsWith("Axes/", StringComparison.Ordinal) && suffixFull.EndsWith("/ServoLoad", StringComparison.Ordinal))
-            {
-                var axisName = suffixFull["Axes/".Length..^"/ServoLoad".Length];
-                if (state.LastServoLoads.TryGetValue(axisName, out var load))
-                    return new DataValueSnapshot(load, FocasStatusMapper.Good, now, now);
-            }
+    /// <summary>
+    ///     How long after a device's last answered fixed-tree poll its cached values stop being
+    ///     served as Good. Eight axis-poll cadences, floored at 30 s so the sub-second default
+    ///     (250 ms) does not make an ordinarily slow CNC flap.
+    /// </summary>
+    /// <param name="pollInterval">The configured fixed-tree poll interval.</param>
+    /// <returns>The staleness budget.</returns>
+    internal static TimeSpan FixedTreeStaleAfter(TimeSpan pollInterval) =>
+        TimeSpan.FromTicks(Math.Max(pollInterval.Ticks * 8, TimeSpan.FromSeconds(30).Ticks));
 
-            // Spindle matches: "{host}/Spindle/{name}/Load" + "{host}/Spindle/{name}/MaxRpm"
-            if (suffixFull.StartsWith("Spindle/", StringComparison.Ordinal)
-                && state.FixedTreeCache is { } spindleCache)
+    /// <summary>
+    ///     Resolves one fixed-tree <paramref name="path"/> (<c>Identity/SeriesNumber</c>,
+    ///     <c>Axes/X/AbsolutePosition</c>, …) against a single device's caches. Returns null when
+    ///     this device's fixed tree has no such path — the caller decides what that means.
+    /// </summary>
+    /// <param name="state">The device whose caches to read.</param>
+    /// <param name="path">The fixed-tree path, with no device prefix.</param>
+    /// <param name="now">The read timestamp.</param>
+    /// <returns>The snapshot, or null when the path names nothing on this device.</returns>
+    /// <remarks>
+    ///     Values are dated from <see cref="DeviceState.LastFixedPollUtc"/>, not from
+    ///     <paramref name="now"/>, and go <c>BadCommunicationError</c> once that stamp is older than
+    ///     <see cref="FixedTreeStaleAfter"/>. A cache hit deliberately does NOT advance driver health:
+    ///     the value came from the poll loop, not from this call, and crediting it would let a driver
+    ///     serving nothing but fixed-tree tags report a fresh successful read while its CNC was gone.
+    /// </remarks>
+    private DataValueSnapshot? TryReadFixedTreeOnDevice(DeviceState state, string path, DateTime now)
+    {
+        var polledUtc = state.LastFixedPollUtc;
+        if (polledUtc is null) return null;
+        var status = now - polledUtc.Value > FixedTreeStaleAfter(_options.FixedTree.PollInterval)
+            ? FocasStatusMapper.BadCommunicationError
+            : FocasStatusMapper.Good;
+        var sourceUtc = polledUtc.Value;
+
+        if (state.LastFixedSnapshots.TryGetValue(
+                FixedTreeReference(state.Options.HostAddress, path), out var raw))
+            return new DataValueSnapshot(raw, status, sourceUtc, now);
+
+        // Servo-load match: path shape is "Axes/{name}/ServoLoad"
+        var suffixFull = path;
+        if (suffixFull.StartsWith("Axes/", StringComparison.Ordinal) && suffixFull.EndsWith("/ServoLoad", StringComparison.Ordinal))
+        {
+            var axisName = suffixFull["Axes/".Length..^"/ServoLoad".Length];
+            if (state.LastServoLoads.TryGetValue(axisName, out var load))
+                return new DataValueSnapshot(load, status, sourceUtc, now);
+        }
+
+        // Spindle matches: "Spindle/{name}/Load" + "Spindle/{name}/MaxRpm"
+        if (suffixFull.StartsWith("Spindle/", StringComparison.Ordinal)
+            && state.FixedTreeCache is { } spindleCache)
+        {
+            var tail = suffixFull["Spindle/".Length..];
+            var slash = tail.IndexOf('/');
+            if (slash > 0)
             {
-                var tail = suffixFull["Spindle/".Length..];
-                var slash = tail.IndexOf('/');
-                if (slash > 0)
+                var spindleName = tail[..slash];
+                var field = tail[(slash + 1)..];
+                var idx = -1;
+                for (var i = 0; i < spindleCache.Spindles.Count; i++)
                 {
-                    var spindleName = tail[..slash];
-                    var field = tail[(slash + 1)..];
-                    var idx = -1;
-                    for (var i = 0; i < spindleCache.Spindles.Count; i++)
+                    var s = spindleCache.Spindles[i];
+                    var display = string.IsNullOrEmpty(s.Display) ? $"S{i + 1}" : s.Display;
+                    if (string.Equals(display, spindleName, StringComparison.OrdinalIgnoreCase)) { idx = i; break; }
+                }
+                if (idx >= 0)
+                {
+                    object? value = field switch
                     {
-                        var s = spindleCache.Spindles[i];
-                        var display = string.IsNullOrEmpty(s.Display) ? $"S{i + 1}" : s.Display;
-                        if (string.Equals(display, spindleName, StringComparison.OrdinalIgnoreCase)) { idx = i; break; }
-                    }
-                    if (idx >= 0)
-                    {
-                        object? value = field switch
-                        {
-                            "Load" => state.LastSpindleLoads.TryGetValue(idx, out var l) ? (object)l : null,
-                            "MaxRpm" => idx < spindleCache.SpindleMaxRpms.Count ? (object)spindleCache.SpindleMaxRpms[idx] : null,
-                            _ => null,
-                        };
-                        if (value is not null)
-                            return new DataValueSnapshot(value, FocasStatusMapper.Good, now, now);
-                    }
+                        "Load" => state.LastSpindleLoads.TryGetValue(idx, out var l) ? (object)l : null,
+                        "MaxRpm" => idx < spindleCache.SpindleMaxRpms.Count ? (object)spindleCache.SpindleMaxRpms[idx] : null,
+                        _ => null,
+                    };
+                    if (value is not null)
+                        return new DataValueSnapshot(value, status, sourceUtc, now);
                 }
             }
-            // Identity strings + program / op-mode fields aren't cached as doubles —
-            // re-derive from the struct caches.
-            if (state.FixedTreeCache is { } cache)
+        }
+        // Identity strings + program / op-mode fields aren't cached as doubles —
+        // re-derive from the struct caches.
+        if (state.FixedTreeCache is { } cache)
+        {
+            var value = path switch
             {
-                var suffix = reference[(state.Options.HostAddress.Length + 1)..];
-                var value = suffix switch
-                {
-                    "Identity/SeriesNumber" => (object)cache.SysInfo.Series,
-                    "Identity/Version" => cache.SysInfo.Version,
-                    "Identity/MaxAxes" => cache.SysInfo.MaxAxis,
-                    "Identity/CncType" => cache.SysInfo.CncType,
-                    "Identity/MtType" => cache.SysInfo.MtType,
-                    "Identity/AxisCount" => cache.SysInfo.AxesCount,
-                    "Program/Name" => (object?)state.LastProgramInfo?.Name,
-                    "Program/ONumber" => state.LastProgramInfo?.ONumber,
-                    "Program/BlockCount" => state.LastProgramInfo?.BlockCount,
-                    "Program/Number" => state.LastProgramAxisRef?.ProgramNumber,
-                    "Program/MainNumber" => state.LastProgramAxisRef?.MainProgramNumber,
-                    "Program/Sequence" => state.LastProgramAxisRef?.SequenceNumber,
-                    "OperationMode/Mode" => state.LastProgramInfo?.Mode,
-                    "OperationMode/ModeText" => state.LastProgramInfo is { } pi
-                        ? FocasOpMode.ToText(pi.Mode) : null,
-                    "Timers/PowerOnSeconds" => TimerValue(state, FocasTimerKind.PowerOn),
-                    "Timers/OperatingSeconds" => TimerValue(state, FocasTimerKind.Operating),
-                    "Timers/CuttingSeconds" => TimerValue(state, FocasTimerKind.Cutting),
-                    "Timers/CycleSeconds" => TimerValue(state, FocasTimerKind.Cycle),
-                    _ => null,
-                };
-                if (value is not null)
-                    return new DataValueSnapshot(value, FocasStatusMapper.Good, now, now);
-            }
+                "Identity/SeriesNumber" => (object)cache.SysInfo.Series,
+                "Identity/Version" => cache.SysInfo.Version,
+                "Identity/MaxAxes" => cache.SysInfo.MaxAxis,
+                "Identity/CncType" => cache.SysInfo.CncType,
+                "Identity/MtType" => cache.SysInfo.MtType,
+                "Identity/AxisCount" => cache.SysInfo.AxesCount,
+                "Program/Name" => (object?)state.LastProgramInfo?.Name,
+                "Program/ONumber" => state.LastProgramInfo?.ONumber,
+                "Program/BlockCount" => state.LastProgramInfo?.BlockCount,
+                "Program/Number" => state.LastProgramAxisRef?.ProgramNumber,
+                "Program/MainNumber" => state.LastProgramAxisRef?.MainProgramNumber,
+                "Program/Sequence" => state.LastProgramAxisRef?.SequenceNumber,
+                "OperationMode/Mode" => state.LastProgramInfo?.Mode,
+                "OperationMode/ModeText" => state.LastProgramInfo is { } pi
+                    ? FocasOpMode.ToText(pi.Mode) : null,
+                "Timers/PowerOnSeconds" => TimerValue(state, FocasTimerKind.PowerOn),
+                "Timers/OperatingSeconds" => TimerValue(state, FocasTimerKind.Operating),
+                "Timers/CuttingSeconds" => TimerValue(state, FocasTimerKind.Cutting),
+                "Timers/CycleSeconds" => TimerValue(state, FocasTimerKind.Cycle),
+                _ => null,
+            };
+            if (value is not null)
+                return new DataValueSnapshot(value, status, sourceUtc, now);
         }
         return null;
     }
@@ -1357,6 +1497,21 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
         public CancellationTokenSource? FixedTreeCts { get; set; }
         /// <summary>Gets or sets the fixed-tree cache for this device.</summary>
         public FocasFixedTreeCache? FixedTreeCache { get; set; }
+
+        /// <summary>
+        ///     Gets or sets the UTC time the fixed-tree loop last got an answer out of this device
+        ///     — set when the bootstrap completes and again after each poll tick's axis pass. Null
+        ///     until the device has answered once.
+        /// </summary>
+        /// <remarks>
+        ///     <b>This is what stops a dead CNC publishing its last values as Good forever.</b> The
+        ///     fixed-tree poll loop swallows a failed tick (LogDebug + retry) by design, so a device
+        ///     that stops answering leaves the caches populated and unchanging with nothing marking
+        ///     them stale. That was harmless while nothing could bind to the fixed tree; Gitea #540
+        ///     makes those nodes authorable, so reads are now dated from this stamp and go Bad once
+        ///     it falls outside <see cref="FixedTreeStaleAfter"/>.
+        /// </remarks>
+        public DateTime? LastFixedPollUtc { get; set; }
         /// <summary>
         ///     Gets the last fixed-tree snapshots by field name. Double-typed so axis
         ///     positions can carry the <c>10^PositionDecimalPlaces</c> engineering-unit
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/Pickers/FOCASAddressPickerBody.razor b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/Pickers/FOCASAddressPickerBody.razor
index 1f1cfe2d..5c0a17be 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/Pickers/FOCASAddressPickerBody.razor
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/Pickers/FOCASAddressPickerBody.razor
@@ -1,9 +1,16 @@
 @* FOCAS address picker:
-     1. Static parameter group + parameter ID → axis:5 (always available).
+     1. Manual composition of the three addressed spaces — PMC (X0.0 / R100), CNC parameter
+        (PARAM:1020) and macro variable (MACRO:500) — always available.
      2. (DriverOperator-gated, when the driver supports online discovery) Browse the FixedTree
-        device model captured by the universal DiscoveryDriverBrowser. FOCAS opens take a few
-        seconds longer than other drivers — its FixedTree cache fills post-connect and the browser
-        runs an UntilStable settle loop; the _opening spinner covers the wait. *@
+        device model captured by the universal DiscoveryDriverBrowser, which yields FIXED: paths.
+        FOCAS opens take a few seconds longer than other drivers — its FixedTree cache fills
+        post-connect and the browser runs an UntilStable settle loop; the _opening spinner covers
+        the wait.
+
+     Both branches now emit an address FocasAddress.TryParse accepts. Branch 1 used to offer
+     axis/spindle/program/status "parameter groups", which are not FOCAS addressing spaces, and
+     emitted "axis:5"; branch 2 committed the browse leaf's host-prefixed full reference. Neither
+     could be read (Gitea #540). *@
 @implements IAsyncDisposable
 @using Microsoft.AspNetCore.Authorization
 @using ZB.MOM.WW.OtOpcUa.AdminUI.Browsing
@@ -14,20 +21,43 @@
 @inject IAuthorizationService AuthorizationService
 
 <div class="row g-3">
-    <div class="col-md-4">
-        <label class="form-label">Parameter group</label>
-        <select class="form-select form-select-sm" @bind="_group" @bind:after="OnChangedAsync">
-            <option value="axis">axis</option>
-            <option value="spindle">spindle</option>
-            <option value="program">program</option>
-            <option value="status">status</option>
+    <div class="col-md-3">
+        <label class="form-label">Address space</label>
+        <select class="form-select form-select-sm" @bind="_kind" @bind:after="OnChangedAsync">
+            <option value="@FocasManualAddressKind.Pmc">PMC</option>
+            <option value="@FocasManualAddressKind.Parameter">CNC parameter</option>
+            <option value="@FocasManualAddressKind.Macro">Macro variable</option>
         </select>
     </div>
+    @if (_kind == FocasManualAddressKind.Pmc)
+    {
+        <div class="col-md-2">
+            <label class="form-label">Area</label>
+            <select class="form-select form-select-sm" @bind="_pmcLetter" @bind:after="OnChangedAsync">
+                @foreach (var letter in FocasAddressBuilder.PmcLetters)
+                {
+                    <option value="@letter">@letter</option>
+                }
+            </select>
+        </div>
+    }
     <div class="col-md-3">
-        <label class="form-label">Parameter ID</label>
+        <label class="form-label">@(_kind == FocasManualAddressKind.Pmc ? "Byte" : "Number")</label>
         <input type="number" class="form-control form-control-sm" min="0"
-               @bind="_parameterId" @bind:after="OnChangedAsync" />
+               @bind="_number" @bind:after="OnChangedAsync" />
     </div>
+    @if (_kind != FocasManualAddressKind.Macro)
+    {
+        <div class="col-md-3">
+            <label class="form-label">
+                Bit <span class="text-muted small">(optional, @(_kind == FocasManualAddressKind.Pmc ? "0-7" : "0-31"))</span>
+            </label>
+            <input type="number" class="form-control form-control-sm" min="0"
+                   max="@(_kind == FocasManualAddressKind.Pmc ? 7 : 31)"
+                   placeholder="whole word"
+                   @bind="_bitIndex" @bind:after="OnChangedAsync" />
+        </div>
+    }
 </div>
 
 @if (_canBrowse)
@@ -68,7 +98,14 @@
 
 <div class="mt-3">
     <span class="text-muted small">Result:</span>
-    <code class="mono ms-2">@_built</code>
+    @if (string.IsNullOrEmpty(_built))
+    {
+        <span class="chip chip-bad ms-2">not a valid address</span>
+    }
+    else
+    {
+        <code class="mono ms-2">@_built</code>
+    }
 </div>
 
 @code {
@@ -79,8 +116,10 @@
     /// <summary>Live accessor for the selected driver's DriverConfig JSON (browse connect config).</summary>
     [Parameter] public Func<string> GetConfigJson { get; set; } = () => "{}";
 
-    private string _group = "axis";
-    private int _parameterId = 0;
+    private FocasManualAddressKind _kind = FocasManualAddressKind.Pmc;
+    private string _pmcLetter = "R";
+    private int _number = 0;
+    private int? _bitIndex;
     private string _built = "";
 
     private Guid _token = Guid.Empty;
@@ -94,7 +133,7 @@
         var authResult = await AuthorizationService.AuthorizeAsync(auth.User, null, AdminUiPolicies.DriverOperator);
         // CanBrowse constructs a throwaway driver — evaluate once, not per render.
         _canBrowse = authResult.Succeeded && BrowserService.CanBrowse(DriverType, GetConfigJson() ?? "{}");
-        _built = FocasAddressBuilder.Build(_group, _parameterId);
+        _built = FocasAddressBuilder.Build(_kind, _pmcLetter, _number, _bitIndex);
         await CurrentAddressChanged.InvokeAsync(_built);
     }
 
@@ -125,8 +164,9 @@
 
     private async Task OnTreeSelectAsync(BrowseNode node)
     {
-        // Folders fire the same callback — commit only on a leaf. The captured NodeId is the
-        // driver FullName (FixedTree address), which the group/id builder cannot reconstruct, so
+        // Folders fire the same callback — commit only on a leaf. The captured NodeId is the driver
+        // FullName, which for a fixed-tree leaf is its canonical FIXED: address (Gitea #540); the
+        // manual builder composes only the three addressed spaces and cannot reconstruct it, so
         // commit it directly rather than through OnChangedAsync.
         if (node.Kind != BrowseNodeKind.Leaf) return;
         _built = node.NodeId;
@@ -135,7 +175,7 @@
 
     private async Task OnChangedAsync()
     {
-        _built = FocasAddressBuilder.Build(_group, _parameterId);
+        _built = FocasAddressBuilder.Build(_kind, _pmcLetter, _number, _bitIndex);
         await CurrentAddressChanged.InvokeAsync(_built);
     }
 
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/Pickers/FocasAddressBuilder.cs b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/Pickers/FocasAddressBuilder.cs
index 94e2708d..3c52af1d 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/Pickers/FocasAddressBuilder.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/Pickers/FocasAddressBuilder.cs
@@ -1,16 +1,76 @@
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
 namespace ZB.MOM.WW.OtOpcUa.AdminUI.Components.Shared.Drivers.Pickers;
 
 /// <summary>
-/// Pure static helper that converts a FOCAS parameter group + parameter ID
-/// into the canonical address string (e.g. axis:5).
+/// The addressing spaces the manual FOCAS picker can compose. Mirrors the parseable subset of
+/// <see cref="FocasAreaKind"/>: <see cref="FocasAreaKind.Fixed"/> is deliberately absent because a
+/// fixed-tree path is discovered from the machine, not composed from parts — the picker's browse
+/// tree supplies those.
+/// </summary>
+public enum FocasManualAddressKind
+{
+    /// <summary>PMC area — letter + byte + optional bit.</summary>
+    Pmc,
+
+    /// <summary>CNC parameter number + optional bit.</summary>
+    Parameter,
+
+    /// <summary>Macro variable number.</summary>
+    Macro,
+}
+
+/// <summary>
+/// Pure static helper that composes a canonical FOCAS address from the manual picker's parts.
 /// Extracted so unit tests can call it without bUnit.
 /// </summary>
+/// <remarks>
+///     <para>
+///     <b>It builds through <see cref="FocasAddress"/> rather than formatting a string</b>, so what
+///     it emits is parseable by construction and the two cannot drift.
+///     </para>
+///     <para>
+///     It previously emitted <c>$"{group}:{parameterId}"</c> over a group list of
+///     <c>axis/spindle/program/status</c> — none of which is a FOCAS addressing space — so the
+///     picker's own default value, <c>axis:5</c>, was an address the driver rejects. Together with
+///     the browse-commit defect this meant every UI-assisted authoring path produced unusable tags,
+///     and only hand-typed addresses worked at all (Gitea #540).
+///     </para>
+/// </remarks>
 public static class FocasAddressBuilder
 {
-    /// <summary>Builds the canonical FOCAS address string from a parameter group and parameter ID.</summary>
-    /// <param name="group">The FOCAS parameter group (e.g. <c>"axis"</c>).</param>
-    /// <param name="parameterId">The parameter ID within the group.</param>
-    /// <returns>The canonical address string in <c>group:parameterId</c> form (e.g. <c>axis:5</c>).</returns>
-    public static string Build(string group, int parameterId)
-        => $"{group}:{parameterId}";
+    /// <summary>The PMC area letters the driver accepts, in the order the picker offers them.</summary>
+    public static IReadOnlyList<string> PmcLetters { get; } =
+        ["X", "Y", "F", "G", "R", "D", "C", "K", "A", "E", "T"];
+
+    /// <summary>
+    /// Composes the canonical FOCAS address string, or an empty string when the parts do not form a
+    /// valid address (an out-of-range bit, a negative number, an unknown PMC letter).
+    /// </summary>
+    /// <param name="kind">Which addressing space the address is in.</param>
+    /// <param name="pmcLetter">The PMC area letter; ignored unless <paramref name="kind"/> is
+    /// <see cref="FocasManualAddressKind.Pmc"/>.</param>
+    /// <param name="number">The PMC byte, parameter number or macro number.</param>
+    /// <param name="bitIndex">Optional bit index — 0–7 for PMC, 0–31 for a parameter. Null for a
+    /// whole-word address; always ignored for a macro, which has no bit form.</param>
+    /// <returns>The canonical address, or an empty string when the parts are not addressable.</returns>
+    public static string Build(
+        FocasManualAddressKind kind, string? pmcLetter, int number, int? bitIndex)
+    {
+        FocasAddress? candidate = kind switch
+        {
+            FocasManualAddressKind.Pmc => new FocasAddress(
+                FocasAreaKind.Pmc, (pmcLetter ?? "").Trim().ToUpperInvariant(), number, bitIndex),
+            FocasManualAddressKind.Parameter => new FocasAddress(
+                FocasAreaKind.Parameter, null, number, bitIndex),
+            FocasManualAddressKind.Macro => new FocasAddress(
+                FocasAreaKind.Macro, null, number, null),
+            _ => null,
+        };
+
+        // Round-trip rather than trust the parts: the record accepts any values, the parser is the
+        // authority on which of them address anything, and an empty result is what the picker shows
+        // as "no address yet" instead of a plausible-looking string the driver would silently skip.
+        return candidate?.Canonical is { } text && FocasAddress.TryParse(text) is not null ? text : "";
+    }
 }
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/FocasTagConfigModel.cs b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/FocasTagConfigModel.cs
index ac159401..b7a22faf 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/FocasTagConfigModel.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/FocasTagConfigModel.cs
@@ -47,6 +47,32 @@ public sealed class FocasTagConfigModel
 
     /// <summary>Validation hook; returns an error message or null when the model is valid.</summary>
     /// <returns>An error message describing the validation failure, or null when the model is valid.</returns>
+    /// <remarks>
+    ///     <b>This runs the driver's real parser, not a non-empty check</b> (Gitea #540). It used to
+    ///     accept any non-blank string, which is how 20 tags carrying a browse full reference
+    ///     (<c>10.201.31.5:8193/Identity/SeriesNumber</c>) were authored, deployed and sealed green —
+    ///     the driver then skipped every one at init and they read <c>BadNodeIdUnknown</c> forever
+    ///     with no signal anywhere. An address that cannot be parsed cannot be polled, so the
+    ///     rejection belongs here, where the operator is still looking at the field.
+    ///     <para><see cref="FocasAddress"/> lives in the driver's <c>Contracts</c> assembly precisely
+    ///     so this project can call it without referencing the runtime driver (Gitea #526).</para>
+    /// </remarks>
     public string? Validate()
-        => string.IsNullOrWhiteSpace(Address) ? "Address is required." : null;
+    {
+        if (string.IsNullOrWhiteSpace(Address)) return "Address is required.";
+        return FocasAddress.TryParse(Address) is null ? DescribeUnparseableAddress(Address) : null;
+    }
+
+    /// <summary>
+    ///     The operator-facing rejection message for an address the FOCAS parser will not accept,
+    ///     naming the four legal forms. Shared with the deploy-time inspector so the modal and the
+    ///     deploy gate say the same thing about the same string.
+    /// </summary>
+    /// <param name="address">The rejected address.</param>
+    /// <returns>The message.</returns>
+    internal static string DescribeUnparseableAddress(string address) =>
+        $"'{address.Trim()}' is not a FOCAS address. Expected a PMC address (X0.0, R100, F20.3), " +
+        "a CNC parameter (PARAM:1020, PARAM:1815/0), a macro variable (MACRO:500), or a fixed-tree " +
+        "path (FIXED:Identity/SeriesNumber). A browse full reference including the device host is " +
+        "not an address — commit the leaf from the browser rather than pasting its id.";
 }
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasAddressFixedFormTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasAddressFixedFormTests.cs
new file mode 100644
index 00000000..2bbb14a0
--- /dev/null
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasAddressFixedFormTests.cs
@@ -0,0 +1,90 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;
+
+/// <summary>
+///     The <c>FIXED:</c> address form added by Gitea #540, and the guarantee that adding it did not
+///     disturb the three forms that were already there.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class FocasAddressFixedFormTests
+{
+    [Theory]
+    [InlineData("FIXED:Identity/SeriesNumber", "Identity/SeriesNumber")]
+    [InlineData("FIXED:Axes/X/AbsolutePosition", "Axes/X/AbsolutePosition")]
+    [InlineData("FIXED:Timers/PowerOnSeconds", "Timers/PowerOnSeconds")]
+    [InlineData("FIXED:Spindle/S1/Load", "Spindle/S1/Load")]
+    [InlineData("fixed:Program/Name", "Program/Name")]          // prefix is case-insensitive
+    [InlineData("  FIXED:Program/Name  ", "Program/Name")]       // outer whitespace tolerated
+    public void Parses_a_fixed_tree_path(string input, string expectedPath)
+    {
+        var parsed = FocasAddress.TryParse(input);
+
+        parsed.ShouldNotBeNull();
+        parsed.Kind.ShouldBe(FocasAreaKind.Fixed);
+        parsed.FixedPath.ShouldBe(expectedPath);
+        parsed.Canonical.ShouldBe("FIXED:" + expectedPath);
+    }
+
+    [Theory]
+    [InlineData("FIXED:")]                       // no path
+    [InlineData("FIXED:   ")]
+    [InlineData("FIXED:/Identity/Series")]       // leading separator
+    [InlineData("FIXED:Identity/Series/")]       // trailing separator
+    [InlineData("FIXED:Identity//Series")]       // empty segment
+    [InlineData("FIXED:Identity/ /Series")]      // blank segment
+    [InlineData("FIXED:MACRO:500")]              // a colon would make the grammar ambiguous
+    public void Rejects_a_path_that_is_not_addressable(string input)
+        => FocasAddress.TryParse(input).ShouldBeNull();
+
+    /// <summary>
+    ///     The exact strings the defect produced. Each names a real fixed-tree field but carries the
+    ///     device host, which is the tag's Device row's job — so they must still be rejected rather
+    ///     than quietly accepted with the host treated as a path segment.
+    /// </summary>
+    [Theory]
+    [InlineData("10.201.31.5:8193/Identity/SeriesNumber")]
+    [InlineData("focas://10.201.31.5:8193/Axes/X/AbsolutePosition")]
+    [InlineData("axis:5")]     // the manual picker's old default
+    public void Still_rejects_what_the_defect_authored(string input)
+        => FocasAddress.TryParse(input).ShouldBeNull();
+
+    /// <summary>
+    ///     <c>F</c> is a valid PMC area letter, so the <c>FIXED:</c> prefix has to be tested before
+    ///     the PMC branch. Both forms must survive that ordering.
+    /// </summary>
+    [Fact]
+    public void The_fixed_prefix_does_not_shadow_the_pmc_F_area()
+    {
+        FocasAddress.TryParse("F20.3")!.Kind.ShouldBe(FocasAreaKind.Pmc);
+        FocasAddress.TryParse("F20.3")!.PmcLetter.ShouldBe("F");
+        FocasAddress.TryParse("FIXED:Program/Name")!.Kind.ShouldBe(FocasAreaKind.Fixed);
+    }
+
+    [Theory]
+    [InlineData("R100")]
+    [InlineData("X0.0")]
+    [InlineData("PARAM:1020")]
+    [InlineData("PARAM:1815/0")]
+    [InlineData("MACRO:500")]
+    public void The_pre_existing_forms_still_round_trip(string input)
+    {
+        var parsed = FocasAddress.TryParse(input);
+
+        parsed.ShouldNotBeNull();
+        parsed.Kind.ShouldNotBe(FocasAreaKind.Fixed);
+        parsed.Canonical.ShouldBe(input);
+    }
+
+    /// <summary>The one place the <c>FIXED:</c> spelling is built, so emitter and parser cannot drift.</summary>
+    [Fact]
+    public void ForFixedPath_produces_what_TryParse_accepts()
+    {
+        var built = FocasAddress.ForFixedPath("Identity/SeriesNumber");
+
+        built.ShouldBe("FIXED:Identity/SeriesNumber");
+        FocasAddress.TryParse(built)!.FixedPath.ShouldBe("Identity/SeriesNumber");
+    }
+}
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasFixedTreeAddressingTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasFixedTreeAddressingTests.cs
new file mode 100644
index 00000000..f8f4a99a
--- /dev/null
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasFixedTreeAddressingTests.cs
@@ -0,0 +1,275 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;
+
+/// <summary>
+///     Gitea #540 — authoring a fixed-tree tag through <c>/raw</c> → Browse device… produced a tag
+///     the driver could never read. The browse leaf's full reference was <c>{deviceHost}/{path}</c>,
+///     the commit mapper wrote it verbatim into <c>TagConfig.address</c>, and
+///     <see cref="FocasAddress.TryParse"/> accepts no such form — so the driver skipped the tag at
+///     init and every read returned <c>BadNodeIdUnknown</c>, indefinitely, while the deploy sealed
+///     green and driver health stayed Healthy with zero errors.
+///     <para>
+///     Found on a real Makino Pro 5 / Fanuc 30i: 0 of 20 browse-committed tags read, while two
+///     hand-authored <c>MACRO:</c> tags on the same device read Good.
+///     </para>
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class FocasFixedTreeAddressingTests
+{
+    private const string Host = "focas://10.0.0.5:8193";
+
+    private static FocasDriver NewDriver(
+        FakeFocasClientFactory factory,
+        bool fixedTreeEnabled,
+        params FocasTagDefinition[] tags) =>
+        new(new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions(Host)],
+            Probe = new FocasProbeOptions { Enabled = false },
+            FixedTree = new FocasFixedTreeOptions { Enabled = fixedTreeEnabled },
+            RawTags = FocasRawTags.Entries(tags),
+        }, "drv-1", factory);
+
+    private static async Task<bool> WaitForAsync(Func<bool> predicate, TimeSpan timeout)
+    {
+        var deadline = DateTime.UtcNow + timeout;
+        while (DateTime.UtcNow < deadline)
+        {
+            if (predicate()) return true;
+            await Task.Delay(25);
+        }
+        return predicate();
+    }
+
+    /// <summary>
+    ///     The headline regression, stated over the WHOLE emitted tree rather than a sample: nothing
+    ///     the browser can offer is unauthorable. Sampling is what let this ship — the tree looked
+    ///     right, and no test ever asked whether the strings hanging off it were addresses.
+    /// </summary>
+    [Fact]
+    public async Task Every_browse_emitted_leaf_carries_an_address_the_driver_can_parse()
+    {
+        var drv = NewDriver(new FakeFocasClientFactory(), fixedTreeEnabled: true);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        (await WaitForAsync(
+            () => drv.GetDeviceState(Host)?.FixedTreeCache is not null, TimeSpan.FromSeconds(5)))
+            .ShouldBeTrue("the fixed-tree cache never filled, so the tree under test was empty");
+
+        var builder = new RecordingBuilder();
+        await drv.DiscoverAsync(builder, CancellationToken.None);
+
+        builder.Variables.ShouldNotBeEmpty();
+        foreach (var (browseName, info) in builder.Variables)
+        {
+            FocasAddress.TryParse(info.FullName)
+                .ShouldNotBeNull($"leaf '{browseName}' emitted '{info.FullName}', which is not an address");
+            // The specific shape that broke it: the device host leaking into the address, where it
+            // is both unparseable and a second routing channel competing with the tag's Device row.
+            info.FullName.ShouldNotContain("10.0.0.5");
+        }
+
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    /// <summary>
+    ///     The end-to-end claim the issue is about: take what the browser offers, author it as a tag,
+    ///     and read it. Anything short of this passed before the fix.
+    /// </summary>
+    [Fact]
+    public async Task A_leaf_authored_from_the_browse_tree_reads_its_value()
+    {
+        // 1. Browse.
+        var browseDrv = NewDriver(new FakeFocasClientFactory(), fixedTreeEnabled: true);
+        await browseDrv.InitializeAsync("{}", CancellationToken.None);
+        (await WaitForAsync(
+            () => browseDrv.GetDeviceState(Host)?.FixedTreeCache is not null, TimeSpan.FromSeconds(5)))
+            .ShouldBeTrue();
+        var builder = new RecordingBuilder();
+        await browseDrv.DiscoverAsync(builder, CancellationToken.None);
+        await browseDrv.ShutdownAsync(CancellationToken.None);
+
+        var seriesLeaf = builder.Variables.Single(v => v.Info.FullName == "FIXED:Identity/SeriesNumber");
+
+        // 2. Commit it as a raw tag, exactly as the browse-commit mapper does — the leaf's full
+        //    reference becomes the tag's address, and its RawPath is where the operator put it.
+        var runDrv = NewDriver(
+            new FakeFocasClientFactory(),
+            fixedTreeEnabled: true,
+            new FocasTagDefinition(
+                "focas-cnc/cnc/FOCAS/cnc/Identity/SeriesNumber",
+                Host,
+                seriesLeaf.Info.FullName,
+                FocasDataType.String,
+                Writable: false));
+        await runDrv.InitializeAsync("{}", CancellationToken.None);
+        (await WaitForAsync(
+            () => runDrv.GetDeviceState(Host)?.FixedTreeCache is not null, TimeSpan.FromSeconds(5)))
+            .ShouldBeTrue();
+
+        // 3. Read it by RawPath, which is the reference the v3 server uses.
+        var read = await runDrv.ReadAsync(["focas-cnc/cnc/FOCAS/cnc/Identity/SeriesNumber"], CancellationToken.None);
+
+        read[0].StatusCode.ShouldBe(FocasStatusMapper.Good);
+        read[0].Value.ShouldBe("30i");   // FakeFocasClient.SysInfo.Series
+        await runDrv.ShutdownAsync(CancellationToken.None);
+    }
+
+    /// <summary>
+    ///     <c>FixedTree.Enabled</c> defaults to false and the universal browser force-enables it only
+    ///     for the duration of a browse. Without this, an operator would browse the tree, commit
+    ///     leaves, deploy, and land on a driver whose poll loop never starts — every tag Bad, with a
+    ///     perfectly correct address. Authoring a FIXED: tag is the request for the tree.
+    /// </summary>
+    [Fact]
+    public async Task An_authored_fixed_tag_arms_the_poll_loop_with_the_config_flag_off()
+    {
+        var drv = NewDriver(
+            new FakeFocasClientFactory(),
+            fixedTreeEnabled: false,
+            new FocasTagDefinition("raw/Program", Host, "FIXED:Program/Name", FocasDataType.String, Writable: false));
+
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        (await WaitForAsync(
+            () => drv.GetDeviceState(Host)?.FixedTreeCache is not null, TimeSpan.FromSeconds(5)))
+            .ShouldBeTrue("an authored FIXED: tag must start the fixed-tree loop on its own");
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    /// <summary>A driver with no fixed-tree tags and the flag off must still not start the loop.</summary>
+    [Fact]
+    public async Task An_ordinary_tag_does_not_arm_the_poll_loop()
+    {
+        var drv = NewDriver(
+            new FakeFocasClientFactory(),
+            fixedTreeEnabled: false,
+            new FocasTagDefinition("raw/Run", Host, "R100", FocasDataType.Byte));
+
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await Task.Delay(300);
+
+        drv.GetDeviceState(Host)!.FixedTreeCache.ShouldBeNull();
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    /// <summary>
+    ///     A path this machine does not expose is a genuine <c>BadNodeIdUnknown</c> — the address
+    ///     parsed, it simply names nothing here (a capability the series lacks, a renamed axis).
+    /// </summary>
+    [Fact]
+    public async Task A_fixed_path_the_machine_does_not_expose_reads_BadNodeIdUnknown()
+    {
+        var drv = NewDriver(
+            new FakeFocasClientFactory(),
+            fixedTreeEnabled: true,
+            new FocasTagDefinition("raw/Ghost", Host, "FIXED:Axes/Q/AbsolutePosition", FocasDataType.Float64, Writable: false));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        (await WaitForAsync(
+            () => drv.GetDeviceState(Host)?.LastFixedPollUtc is not null, TimeSpan.FromSeconds(5)))
+            .ShouldBeTrue();
+
+        var read = await drv.ReadAsync(["raw/Ghost"], CancellationToken.None);
+
+        read[0].StatusCode.ShouldBe(FocasStatusMapper.BadNodeIdUnknown);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    /// <summary>
+    ///     Nothing in the fixed tree is a writable location on the CNC — it is a read-out of machine
+    ///     state. Refused before a connection is opened.
+    /// </summary>
+    [Fact]
+    public async Task A_fixed_tree_tag_refuses_writes()
+    {
+        var drv = NewDriver(
+            new FakeFocasClientFactory(),
+            fixedTreeEnabled: true,
+            // Writable:true on purpose — the refusal must come from the address kind, not from the
+            // tag's own flag, or an operator could author their way past it.
+            new FocasTagDefinition("raw/Series", Host, "FIXED:Identity/SeriesNumber", FocasDataType.String, Writable: true));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("raw/Series", "nope")], CancellationToken.None);
+
+        results[0].StatusCode.ShouldBe(FocasStatusMapper.BadNotWritable);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    /// <summary>
+    ///     A dead CNC must not keep serving its last fixed-tree values as Good. The poll loop
+    ///     swallows a failed tick by design (LogDebug + retry), so nothing else marks the caches
+    ///     stale — and unlike an area read, a fixed-tree read issues no traffic that could fail.
+    ///     This was harmless while nothing could bind to the tree; it is not harmless now.
+    /// </summary>
+    [Fact]
+    public async Task Fixed_tree_values_go_bad_once_the_device_stops_answering()
+    {
+        var drv = NewDriver(
+            new FakeFocasClientFactory(),
+            fixedTreeEnabled: true,
+            new FocasTagDefinition("raw/Series", Host, "FIXED:Identity/SeriesNumber", FocasDataType.String, Writable: false));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        (await WaitForAsync(
+            () => drv.GetDeviceState(Host)?.LastFixedPollUtc is not null, TimeSpan.FromSeconds(5)))
+            .ShouldBeTrue();
+
+        (await drv.ReadAsync(["raw/Series"], CancellationToken.None))[0]
+            .StatusCode.ShouldBe(FocasStatusMapper.Good);
+
+        // Age the last answered poll past the staleness budget. Reaching into DeviceState rather
+        // than sleeping keeps this deterministic and instant; the budget itself is asserted below.
+        var state = drv.GetDeviceState(Host)!;
+        state.FixedTreeCts?.Cancel();
+        state.LastFixedPollUtc = DateTime.UtcNow
+            - FocasDriver.FixedTreeStaleAfter(TimeSpan.FromMilliseconds(250))
+            - TimeSpan.FromSeconds(1);
+
+        var stale = await drv.ReadAsync(["raw/Series"], CancellationToken.None);
+
+        stale[0].StatusCode.ShouldBe(FocasStatusMapper.BadCommunicationError);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    /// <summary>
+    ///     The staleness budget tracks the poll cadence but never drops below 30 s, so an ordinarily
+    ///     slow CNC on the sub-second default cadence does not flap between Good and Bad.
+    /// </summary>
+    [Theory]
+    [InlineData(250, 30_000)]        // default cadence — the 30 s floor wins
+    [InlineData(1_000, 30_000)]      // 8 s of cadence still under the floor
+    [InlineData(10_000, 80_000)]     // slow cadence — 8x the interval wins
+    public void Stale_budget_is_eight_cadences_floored_at_thirty_seconds(int pollMs, int expectedMs)
+        => FocasDriver.FixedTreeStaleAfter(TimeSpan.FromMilliseconds(pollMs))
+            .ShouldBe(TimeSpan.FromMilliseconds(expectedMs));
+
+    /// <summary>Records what <c>DiscoverAsync</c> emits, flattening the folder tree.</summary>
+    private sealed class RecordingBuilder : IAddressSpaceBuilder
+    {
+        public List<(string BrowseName, string DisplayName)> Folders { get; } = [];
+        public List<(string BrowseName, DriverAttributeInfo Info)> Variables { get; } = [];
+
+        public IAddressSpaceBuilder Folder(string browseName, string displayName)
+        { Folders.Add((browseName, displayName)); return this; }
+
+        public IVariableHandle Variable(string browseName, string displayName, DriverAttributeInfo info)
+        { Variables.Add((browseName, info)); return new Handle(info.FullName); }
+
+        public void AddProperty(string name, DriverDataType type, object? value) { }
+
+        private sealed class Handle(string fullRef) : IVariableHandle
+        {
+            public string FullReference => fullRef;
+            public IAlarmConditionSink MarkAsAlarmCondition(AlarmConditionInfo info) => new NullSink();
+        }
+
+        private sealed class NullSink : IAlarmConditionSink
+        {
+            public void OnTransition(AlarmEventArgs args) { }
+        }
+    }
+}
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Pickers/FocasAddressBuilderTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Pickers/FocasAddressBuilderTests.cs
index d95d057a..1edd0323 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Pickers/FocasAddressBuilderTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Pickers/FocasAddressBuilderTests.cs
@@ -1,16 +1,66 @@
 using Shouldly;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.AdminUI.Components.Shared.Drivers.Pickers;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
 
 namespace ZB.MOM.WW.OtOpcUa.AdminUI.Tests.Pickers;
 
+/// <summary>
+///     Gitea #540. The previous edition of this file asserted
+///     <c>Build("axis", 5) == "axis:5"</c> for four "parameter groups" that are not FOCAS
+///     addressing spaces — it pinned the exact string the driver could not parse, which is why
+///     a fully-green suite coexisted with a picker whose default value was unusable. Every case
+///     here therefore asserts the address ROUND-TRIPS through the driver's parser, not merely
+///     that it has the expected shape.
+/// </summary>
 public sealed class FocasAddressBuilderTests
 {
     [Theory]
-    [InlineData("axis", 5, "axis:5")]
-    [InlineData("spindle", 0, "spindle:0")]
-    [InlineData("program", 100, "program:100")]
-    [InlineData("status", 1, "status:1")]
-    public void Build_Canonical(string group, int parameterId, string expected)
-        => FocasAddressBuilder.Build(group, parameterId).ShouldBe(expected);
+    [InlineData(FocasManualAddressKind.Pmc, "R", 100, null, "R100")]
+    [InlineData(FocasManualAddressKind.Pmc, "X", 0, 0, "X0.0")]
+    [InlineData(FocasManualAddressKind.Pmc, "F", 20, 3, "F20.3")]
+    [InlineData(FocasManualAddressKind.Pmc, "r", 100, null, "R100")]      // letter is normalised
+    [InlineData(FocasManualAddressKind.Parameter, null, 1020, null, "PARAM:1020")]
+    [InlineData(FocasManualAddressKind.Parameter, null, 1815, 0, "PARAM:1815/0")]
+    [InlineData(FocasManualAddressKind.Macro, null, 500, null, "MACRO:500")]
+    [InlineData(FocasManualAddressKind.Macro, null, 500, 3, "MACRO:500")]  // macros have no bit form
+    public void Build_produces_an_address_the_driver_can_parse(
+        FocasManualAddressKind kind, string? letter, int number, int? bit, string expected)
+    {
+        var built = FocasAddressBuilder.Build(kind, letter, number, bit);
+
+        built.ShouldBe(expected);
+        FocasAddress.TryParse(built).ShouldNotBeNull();
+    }
+
+    [Theory]
+    [InlineData(FocasManualAddressKind.Pmc, "Z", 10, null)]     // not a PMC area letter
+    [InlineData(FocasManualAddressKind.Pmc, "", 10, null)]      // no area chosen
+    [InlineData(FocasManualAddressKind.Pmc, "R", 10, 8)]        // PMC bits are 0-7
+    [InlineData(FocasManualAddressKind.Pmc, "R", -1, null)]     // negative byte
+    [InlineData(FocasManualAddressKind.Parameter, null, 1815, 32)] // parameter bits are 0-31
+    [InlineData(FocasManualAddressKind.Parameter, null, -5, null)]
+    public void Build_returns_empty_rather_than_an_unusable_address(
+        FocasManualAddressKind kind, string? letter, int number, int? bit)
+        => FocasAddressBuilder.Build(kind, letter, number, bit).ShouldBeEmpty();
+
+    /// <summary>
+    ///     The contract that matters, stated over the whole offered surface rather than a sample:
+    ///     nothing the picker can compose is unreadable. Every PMC area the picker lists, at a
+    ///     whole-word address and at each legal bit.
+    /// </summary>
+    [Fact]
+    public void Every_offered_pmc_area_composes_a_parseable_address()
+    {
+        foreach (var letter in FocasAddressBuilder.PmcLetters)
+        {
+            foreach (int? bit in new int?[] { null, 0, 7 })
+            {
+                var built = FocasAddressBuilder.Build(FocasManualAddressKind.Pmc, letter, 12, bit);
+
+                built.ShouldNotBeEmpty($"PMC area '{letter}' bit '{bit}' composed nothing");
+                FocasAddress.TryParse(built).ShouldNotBeNull($"'{built}' does not parse");
+            }
+        }
+    }
 }
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/FocasTagConfigModelTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/FocasTagConfigModelTests.cs
index f7dbca89..c5d2ae6c 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/FocasTagConfigModelTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/FocasTagConfigModelTests.cs
@@ -74,10 +74,36 @@ public sealed class FocasTagConfigModelTests
         new FocasTagConfigModel { Address = "" }.Validate().ShouldNotBeNull();
     }
 
-    [Fact]
-    public void Validate_returns_null_when_address_filled()
+    [Theory]
+    [InlineData("R100")]
+    [InlineData("X0.0")]
+    [InlineData("PARAM:1815/0")]
+    [InlineData("MACRO:500")]
+    [InlineData("FIXED:Identity/SeriesNumber")]
+    public void Validate_returns_null_for_every_address_form_the_driver_accepts(string address)
+        => new FocasTagConfigModel { Address = address }.Validate().ShouldBeNull();
+
+    /// <summary>
+    ///     Gitea #540. <c>Validate</c> used to accept any non-blank string, so a browse full
+    ///     reference sailed through authoring, through the deploy gate, and was then skipped at
+    ///     driver init — where the only trace was a Debug-level log line nobody reads. The first
+    ///     case here is verbatim what the AdminUI showed for one of the 20 dead tags on the Makino.
+    /// </summary>
+    [Theory]
+    [InlineData("10.201.31.5:8193/Identity/SeriesNumber")]
+    [InlineData("focas://10.201.31.5:8193/Axes/X/AbsolutePosition")]
+    [InlineData("axis:5")]
+    [InlineData("Z99")]                  // Z is not a PMC area letter
+    [InlineData("PARAM:notanumber")]
+    [InlineData("FIXED:")]
+    public void Validate_rejects_an_address_the_driver_would_skip(string address)
     {
-        new FocasTagConfigModel { Address = "R100" }.Validate().ShouldBeNull();
+        var error = new FocasTagConfigModel { Address = address }.Validate();
+
+        error.ShouldNotBeNull();
+        // The operator has to be able to act on it, so the message names the legal forms.
+        error.ShouldContain("PARAM:");
+        error.ShouldContain("FIXED:");
     }
 
     [Fact]
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/RawBrowseCommitMapperTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/RawBrowseCommitMapperTests.cs
index d4cb90b9..79aebcb0 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/RawBrowseCommitMapperTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/RawBrowseCommitMapperTests.cs
@@ -3,6 +3,7 @@ using System.Text.Json.Nodes;
 using Shouldly;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.AdminUI.Uns;
+using ZB.MOM.WW.OtOpcUa.AdminUI.Uns.TagEditors;
 using ZB.MOM.WW.OtOpcUa.Commons.Types;
 using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
@@ -107,6 +108,33 @@ public sealed class RawBrowseCommitMapperTests
     private static Dictionary<string, string> NativeTypeFields(string nativeType) =>
         new() { ["dataType"] = nativeType };
 
+    /// <summary>
+    ///     Gitea #540 — the commit path, judged by whether what it produces is authorable rather
+    ///     than by which key it lands under.
+    ///     <para>
+    ///     The mapper is not where that defect lived: it faithfully wrote the reference the FOCAS
+    ///     browser handed it, which was <c>{deviceHost}/{path}</c> and parses as nothing. The fix
+    ///     was in what the driver emits, so the check that keeps it fixed is that a leaf reference
+    ///     survives the commit AND passes the same validation the modal applies — a mapper test
+    ///     asserting only <c>o["address"] == reference</c> passed happily throughout.
+    ///     </para>
+    /// </summary>
+    /// <param name="reference">A leaf reference of the kind the FOCAS browser emits.</param>
+    [Theory]
+    [InlineData("FIXED:Identity/SeriesNumber")]
+    [InlineData("FIXED:Axes/X/AbsolutePosition")]
+    [InlineData("FIXED:Spindle/S1/Load")]
+    [InlineData("FIXED:Timers/PowerOnSeconds")]
+    [InlineData("MACRO:3901")]
+    public void A_committed_FOCAS_leaf_is_an_address_the_authoring_gate_accepts(string reference)
+    {
+        var json = RawBrowseCommitMapper.BuildTagConfig(DriverTypeNames.FOCAS, reference);
+
+        var model = FocasTagConfigModel.FromJson(json);
+        model.Address.ShouldBe(reference);
+        model.Validate().ShouldBeNull($"'{reference}' committed to a tag the driver would skip");
+    }
+
     /// <summary>
     ///     The committed <c>dataType</c> is the type the CONTROLLER reported, not the model default.
     ///     AB CIP / TwinCAT / FOCAS decode the wire bytes by this field, so a browsed REAL left at the