Merge pull request '[abcip] AbCip — _RefreshTagDb writeable system tag' (#384) from auto/abcip/4.4 into auto/driver-gaps

docs/Driver.AbCip.Cli.md

@@ -89,6 +89,38 @@ otopcua-abcip-cli write -g ab://10.0.0.5/1,0 -t StartCommand --type Bool -v true
 otopcua-abcip-cli subscribe -g ab://10.0.0.5/1,0 -t Motor01_Speed --type Real -i 500
 ```
 
+### `rebrowse` — force a controller-side `@tags` re-walk
+
+PR abcip-2.5 (issue #233) added `RebrowseAsync` to drop the cached UDT
+template shapes and re-run the symbol-table enumerator without restarting
+the driver. The CLI variant builds a transient driver against the supplied
+gateway, runs the rebrowse, and prints the freshly discovered tag names —
+useful after a controller program-download to confirm the new tags are
+visible on the wire before wiring them through the OtOpcUa server.
+
+```powershell
+otopcua-abcip-cli rebrowse -g ab://10.0.0.5/1,0
+```
+
+## Refreshing the tag DB
+
+Two operator-facing surfaces drive the same `RebrowseAsync` plumbing — pick
+the one that matches your context:
+
+| Surface | When to use | Command |
+|---|---|---|
+| **CLI `rebrowse`** | Off-server validation. Spins up a transient driver against the gateway, prints the discovered tag list, no shared state with the live OtOpcUa server. | `otopcua-abcip-cli rebrowse -g ab://10.0.0.5/1,0` |
+| **OPC UA write to `_RefreshTagDb`** | Production / Admin-UI button (PR abcip-4.4). Forces the **live** driver to re-walk + clear its template cache. The `AbCip.RefreshTriggers` driver-diagnostics counter increments per truthy write. | `otopcua-client-cli write -u opc.tcp://localhost:4840 -n "ns=2;s=AbCip/ab://10.0.0.5/1,0/_System/_RefreshTagDb" -v true --type Boolean` |
+
+Read-back semantics: `_RefreshTagDb` always reads back as `false` (Kepware-
+style "latches to idle the moment the dispatch returns") so a subscribed
+client sees a stable shape regardless of how many refreshes have fired.
+Falsy / unparseable writes are no-ops that still report `Good` so a UI
+template that resets the trigger flag after firing it doesn't see a phantom
+error. See
+[AbCip-Operability §System tags](drivers/AbCip-Operability.md#refreshing-the-tag-db-via-opc-ua-write)
+for the full semantics + the diagnostics counter wiring.
+
 ## Typical workflows
 
 - **"Is the PLC reachable?"** → `probe`.
@@ -97,6 +129,10 @@ otopcua-abcip-cli subscribe -g ab://10.0.0.5/1,0 -t Motor01_Speed --type Real -i
 - **"Is this GuardLogix safety tag writable from non-safety?"** → `write` and
   read the status code — safety tags surface `BadNotWritable` / CIP errors,
   non-safety tags surface `Good`.
+- **"Did my program download show up in the address space?"** → `rebrowse`
+  (off-server) or write `true` to the live server's `_RefreshTagDb` system
+  tag (in-server, PR abcip-4.4) — both drop the template cache + force a
+  fresh `@tags` walk.
 
 ## Connection Size
 

docs/drivers/AbCip-Operability.md

@@ -306,17 +306,19 @@ wire up?" to "what's our scan rate / tag count?" without leaving the OPC UA
 address space. The values come straight from the live
 `IHostConnectivityProbe` + `DriverHealth` surfaces — reads bypass libplctag
 and are served from the in-memory snapshot the probe loop / read loop
-updates.
+updates. PR abcip-4.4 added `_RefreshTagDb` as a sixth, writeable entry —
+the Kepware-style refresh trigger.
 
 ### What it ships
 
-| Variable | Type | Source | Notes |
+| Variable | Type | Access | Source | Notes |
-|---|---|---|---|
+|---|---|---|---|---|
-| `_ConnectionStatus` | String | `HostState` | `Running` / `Stopped` / `Unknown` / `Faulted`. Mirrors what the connectivity probe sees. |
+| `_ConnectionStatus` | String | ViewOnly | `HostState` | `Running` / `Stopped` / `Unknown` / `Faulted`. Mirrors what the connectivity probe sees. |
-| `_ScanRate` | Float64 | `AbCipProbeOptions.Interval` | Configured probe interval in milliseconds — compare against `_LastScanTimeMs` to spot wire stretch. |
+| `_ScanRate` | Float64 | ViewOnly | `AbCipProbeOptions.Interval` | Configured probe interval in milliseconds — compare against `_LastScanTimeMs` to spot wire stretch. |
-| `_TagCount` | Int32 | `_tagsByName` | Discovered tag count for this device, excluding `_System/*`. |
+| `_TagCount` | Int32 | ViewOnly | `_tagsByName` | Discovered tag count for this device, excluding `_System/*`. |
-| `_DeviceError` | String | `DriverHealth.LastError` | Most recent error message; empty when the device is healthy. |
+| `_DeviceError` | String | ViewOnly | `DriverHealth.LastError` | Most recent error message; empty when the device is healthy. |
-| `_LastScanTimeMs` | Float64 | `ReadAsync` wall-clock | Duration of the most-recent `ReadAsync` iteration on this device. |
+| `_LastScanTimeMs` | Float64 | ViewOnly | `ReadAsync` wall-clock | Duration of the most-recent `ReadAsync` iteration on this device. |
+| `_RefreshTagDb` | Boolean | **Operate** | n/a (write-only trigger) | PR abcip-4.4 — Kepware-style refresh trigger. Reads always return `false`. Writing any truthy value (`true`, non-zero number, `"true"` / `"1"` strings, case-insensitive) dispatches to `RebrowseAsync` against the device's cached `IAddressSpaceBuilder`. Falsy / unparseable writes are no-ops that report `Good` so a UI that resets the trigger flag doesn't see a phantom error. The `AbCip.RefreshTriggers` diagnostic counter increments per truthy write. |
 
 ### When the snapshot updates
 
@@ -346,19 +348,59 @@ otopcua-client-cli read -u opc.tcp://localhost:4840 \
 
 The driver-side reference embeds the device host address (the
 `_System/<device>/<name>` form) so the dispatcher can route by device
-without an additional registry. PR abcip-4.4 will turn `_RefreshTagDb` into
+without an additional registry. PR abcip-4.4 turned `_RefreshTagDb` into
-a writeable refresh trigger; everything 4.3 ships is `ViewOnly`.
+a writeable refresh trigger; the rest of the surface remains `ViewOnly`.
+
+### Refreshing the tag DB via OPC UA write
+
+PR abcip-4.4 wires `_RefreshTagDb` to the same `RebrowseAsync` entry point
+the CLI's `rebrowse` command exercises (issue #233). Operators have two
+roughly-equivalent ways to force a controller-side `@tags` re-walk after a
+program download:
+
+```powershell
+# Path A — OPC UA write to the system tag (production / Admin UI path)
+otopcua-client-cli write -u opc.tcp://localhost:4840 \
+    -n "ns=2;s=AbCip/ab://10.0.0.5/1,0/_System/_RefreshTagDb" \
+    -v true --type Boolean
+
+# Path B — direct CLI rebrowse against a transient driver (admin / debug path)
+otopcua-abcip-cli rebrowse -g ab://10.0.0.5/1,0
+```
+
+Both paths drop the UDT template cache + re-run the enumerator walk. Path A
+is the operator-facing surface (the same `IDriverControl.RebrowseAsync`
+contract, just dispatched from the OPC UA write surface instead of an
+in-process call). Path B spins up its own driver instance so it doesn't
+share the live server's cache, which makes it useful for one-off
+controller-side validation.
+
+The `AbCip.RefreshTriggers` driver-diagnostics counter increments per
+successful truthy write, so the Admin UI / driver-diagnostics RPC can show
+a "Refreshes since boot" tile that pairs naturally with the existing
+`WritesSuppressed` / `WritesPassedThrough` write-coalescer counters.
 
 ### Verification
 
 - **Unit**: `AbCipSystemTagSourceTests`
   (`tests/.../AbCip.Tests`) — covers snapshot round-trip, two-device
   isolation, recognised-name lookup, default-shape on unseeded devices,
-  discovery emits the five canonical nodes, and `ReadAsync` dispatches
+  discovery emits the six canonical nodes, and `ReadAsync` dispatches
   through the source instead of libplctag.
+- **Unit**: `AbCipRefreshTagDbTests`
+  (`tests/.../AbCip.Tests`) — PR abcip-4.4 — covers discovery emits the
+  trigger as Operate, reads always return `false`, truthy/falsy/null write
+  semantics, the `AbCip.RefreshTriggers` counter, two-device counter
+  independence, defends-in-depth `BadNotWritable` for read-only system
+  variables, no-op-Good when no builder is cached yet, and mixed-batch
+  routing alongside ordinary tag writes.
 - **Integration**: `AbCipSystemTagDiscoveryTests`
   (`tests/.../AbCip.IntegrationTests`) — `[AbServerFact]` connects to a
   real `ab_server`, browses `_System/`, reads each variable, asserts
   every one returns Good with a non-null value.
-- **E2E**: `scripts/e2e/test-abcip.ps1` — see the *SystemTagBrowse*
+- **Integration**: `AbCipRefreshTagDbTests`
-  assertion.
+  (`tests/.../AbCip.IntegrationTests`) — PR abcip-4.4 — `[AbServerFact]`
+  drives a `_RefreshTagDb` write, asserts the template cache drops + the
+  per-device counter advances against a live `ab_server`.
+- **E2E**: `scripts/e2e/test-abcip.ps1` — see the *SystemTagBrowse* +
+  *RefreshTagDbWrite* assertions.

scripts/e2e/test-abcip.ps1

@@ -46,6 +46,14 @@
   runs the SystemTagBrowse assertion — reads the value through the OPC UA
   server + asserts it surfaces one of the canonical HostState strings.
   NodeId form: ns=<n>;s=AbCip/<gateway>/_System/_ConnectionStatus.
+
+.PARAMETER RefreshTagDbNodeId
+  Optional NodeId for the writeable _System/_RefreshTagDb trigger added in
+  PR abcip-4.4. When supplied, the script runs the RefreshTagDbWrite
+  assertion — writes True through the OPC UA server + reads back, asserting
+  the trigger latches to False (Kepware-style "always idle" semantics) and
+  the write itself surfaces Good. NodeId form:
+  ns=<n>;s=AbCip/<gateway>/_System/_RefreshTagDb.
 #>
 
 param(
@@ -60,7 +68,12 @@ param(
     # discovery emits under each device. Optional — when wired, runs the
     # SystemTagBrowse assertion that browses + reads the system folder through the OPC UA
     # server. NodeId form: ns=<n>;s=AbCip/<gateway>/_System/_ConnectionStatus.
-    [string]$SystemConnectionStatusNodeId
+    [string]$SystemConnectionStatusNodeId,
+    # PR abcip-4.4 — NodeId for the writeable _System/_RefreshTagDb refresh-trigger.
+    # Mirrors the SystemConnectionStatusNodeId knob: optional, only runs the
+    # RefreshTagDbWrite assertion when supplied. NodeId form:
+    # ns=<n>;s=AbCip/<gateway>/_System/_RefreshTagDb.
+    [string]$RefreshTagDbNodeId
 )
 
 $ErrorActionPreference = "Stop"
@@ -243,5 +256,42 @@ if ($SystemConnectionStatusNodeId) {
     }
 }
 
+# PR abcip-4.4 — _RefreshTagDb write-then-verify assertion. Writes True through the
+# OPC UA server (the live driver intercepts the write + dispatches to RebrowseAsync
+# against the cached IAddressSpaceBuilder) + reads back, asserting Kepware-style
+# latch semantics: the trigger always reads False the moment the dispatch returns.
+# Pairs with the existing rebrowse step driven by the AbCip CLI (issue #233) — both
+# surfaces hit the same RebrowseAsync entry point, just from different sides of the
+# OPC UA wire.
+if ($RefreshTagDbNodeId) {
+    Write-Header "RefreshTagDbWrite (_System/_RefreshTagDb from $RefreshTagDbNodeId)"
+    $writeArgs = @($opcUaCli.PrefixArgs) + @(
+        "write", "-u", $OpcUaUrl, "-n", $RefreshTagDbNodeId, "-v", "true", "--type", "Boolean")
+    $writeOut = & $opcUaCli.File @writeArgs 2>&1
+    $writeJoined = ($writeOut -join "`n")
+    # The OPC UA Client CLI surfaces "Good" on success; a non-Good result still
+    # round-trips the literal status code so we can match generously.
+    $writeOk = $writeJoined -match "Good"
+
+    $readArgs = @($opcUaCli.PrefixArgs) + @("read", "-u", $OpcUaUrl, "-n", $RefreshTagDbNodeId)
+    $readOut = & $opcUaCli.File @readArgs 2>&1
+    $readJoined = ($readOut -join "`n")
+    # Kepware-style trigger reads always return false — assert the trigger isn't
+    # latched to true after the write. Match case-insensitively because the OPC UA
+    # Client CLI may render the value as "False" or "false".
+    $readFalse = $readJoined -imatch "false"
+
+    $passed = $writeOk -and $readFalse
+    $results += [PSCustomObject]@{
+        Name   = "RefreshTagDbWrite"
+        Passed = $passed
+        Detail = if ($passed) {
+            "_RefreshTagDb write returned Good and read-back surfaced false — Kepware-style latch held"
+        } else {
+            "RefreshTagDb write/verify failed — write='$writeJoined' read='$readJoined'"
+        }
+    }
+}
+
 Write-Summary -Title "AB CIP e2e" -Results $results
 if ($results | Where-Object { -not $_.Passed }) { exit 1 }

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipDriver.cs

@@ -37,6 +37,11 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
     private readonly SemaphoreSlim _discoverySemaphore = new(1, 1);
     private readonly AbCipWriteCoalescer _writeCoalescer = new();
     private readonly AbCipSystemTagSource _systemTagSource = new();
+    // PR abcip-4.4 — cached builder reference so a _RefreshTagDb write can dispatch to
+    // RebrowseAsync without an out-of-band call back into Core. Set by every successful
+    // DiscoverAsync / RebrowseAsync run; null before first discovery (a refresh write that
+    // arrives before the address space exists is a no-op + reports Good).
+    private IAddressSpaceBuilder? _cachedBuilder;
     private DriverHealth _health = new(DriverState.Unknown, null, null);
 
     public event EventHandler<DataChangeEventArgs>? OnDataChange;
@@ -1330,22 +1335,60 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
         ArgumentNullException.ThrowIfNull(writes);
         var results = new WriteResult[writes.Count];
 
+        // PR abcip-4.4 — intercept _System/<host>/_RefreshTagDb writes BEFORE the
+        // multi-write planner runs. These are driver-local control writes: they never
+        // hit libplctag, they're not coalesced, and they don't ride the per-device
+        // bulkhead because the dispatch is in-memory (RebrowseAsync's discovery semaphore
+        // already serialises concurrent refreshes). Truthy writes invoke RebrowseAsync;
+        // falsy / unparseable writes report Good as a no-op so a UI that toggles the
+        // trigger off after firing it doesn't see a phantom error.
+        //
+        // Filter the request list to a non-system slice for the planner so genuine tag
+        // writes still flow through the multi-write packing path unchanged.
+        var nonSystemIndices = new List<int>(writes.Count);
+        for (var i = 0; i < writes.Count; i++)
+        {
+            var w = writes[i];
+            if (AbCipSystemTagSource.IsSystemReference(w.FullReference))
+            {
+                results[i] = await HandleSystemWriteAsync(w, cancellationToken).ConfigureAwait(false);
+            }
+            else
+            {
+                nonSystemIndices.Add(i);
+            }
+        }
+
+        if (nonSystemIndices.Count == 0) return results;
+
+        // Slice the input down to the genuine-tag writes; the planner reports preflight
+        // failures back through the original-index closure so we have to remap.
+        var nonSystemWrites = new WriteRequest[nonSystemIndices.Count];
+        for (var i = 0; i < nonSystemIndices.Count; i++)
+            nonSystemWrites[i] = writes[nonSystemIndices[i]];
+
         var plans = AbCipMultiWritePlanner.Build(
-            writes, _tagsByName, _devices,
+            nonSystemWrites, _tagsByName, _devices,
-            reportPreflight: (idx, code) => results[idx] = new WriteResult(code));
+            reportPreflight: (slicedIdx, code) =>
+                results[nonSystemIndices[slicedIdx]] = new WriteResult(code));
+
+        // PR abcip-4.4 — the planner's OriginalIndex addresses the sliced input list, so
+        // every write back into the caller-visible results array translates through
+        // nonSystemIndices to land at the right slot.
+        int Remap(int slicedIdx) => nonSystemIndices[slicedIdx];
 
         foreach (var plan in plans)
         {
             if (!_devices.TryGetValue(plan.DeviceHostAddress, out var device))
             {
-                foreach (var e in plan.Packable) results[e.OriginalIndex] = new WriteResult(AbCipStatusMapper.BadNodeIdUnknown);
+                foreach (var e in plan.Packable) results[Remap(e.OriginalIndex)] = new WriteResult(AbCipStatusMapper.BadNodeIdUnknown);
-                foreach (var e in plan.BitRmw) results[e.OriginalIndex] = new WriteResult(AbCipStatusMapper.BadNodeIdUnknown);
+                foreach (var e in plan.BitRmw) results[Remap(e.OriginalIndex)] = new WriteResult(AbCipStatusMapper.BadNodeIdUnknown);
                 continue;
             }
 
             // Bit-RMW writes always serialise per-parent — never packed.
             foreach (var entry in plan.BitRmw)
-                results[entry.OriginalIndex] = new WriteResult(
+                results[Remap(entry.OriginalIndex)] = new WriteResult(
                     await ExecuteBitRmwWriteAsync(device, entry, cancellationToken).ConfigureAwait(false));
 
             if (plan.Packable.Count == 0) continue;
@@ -1362,7 +1405,7 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
                 }
                 var outcomes = await Task.WhenAll(tasks).ConfigureAwait(false);
                 foreach (var (idx, code) in outcomes)
-                    results[idx] = new WriteResult(code);
+                    results[Remap(idx)] = new WriteResult(code);
             }
             else
             {
@@ -1371,7 +1414,7 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
                 {
                     var code = await ExecutePackableWriteAsync(device, entry, cancellationToken)
                         .ConfigureAwait(false);
-                    results[entry.OriginalIndex] = new WriteResult(code.code);
+                    results[Remap(entry.OriginalIndex)] = new WriteResult(code.code);
                 }
             }
         }
@@ -1379,6 +1422,66 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
         return results;
     }
 
+    /// <summary>
+    ///     PR abcip-4.4 — handle a write against a <c>_System/&lt;host&gt;/&lt;name&gt;</c>
+    ///     reference. Today only <c>_RefreshTagDb</c> is writeable; everything else under
+    ///     <c>_System/</c> is <see cref="SecurityClassification.ViewOnly"/> + the OPC UA
+    ///     server layer rejects the write before it reaches the driver. The driver still
+    ///     defends in depth here: an unrecognised system-tag write reports
+    ///     <see cref="AbCipStatusMapper.BadNotWritable"/> rather than silently succeeding.
+    /// </summary>
+    private async Task<WriteResult> HandleSystemWriteAsync(WriteRequest write, CancellationToken cancellationToken)
+    {
+        var deviceHost = ExtractSystemDeviceHost(write.FullReference);
+        var nameUnderSystem = ExtractSystemTagName(write.FullReference);
+        if (deviceHost is null || nameUnderSystem is null)
+            return new WriteResult(AbCipStatusMapper.BadNodeIdUnknown);
+
+        if (!AbCipSystemTagSource.IsRefreshTagDb(nameUnderSystem))
+        {
+            // Read-only system variable — the server-layer ACL should already have
+            // rejected this, but defend in depth so a misconfigured client gets a
+            // recognisable error instead of "Good but nothing happened".
+            return new WriteResult(AbCipStatusMapper.BadNotWritable);
+        }
+
+        // Falsy / unparseable writes are a no-op so a UI that resets the trigger flag
+        // back to false (after firing it) doesn't see a phantom error. Good is the same
+        // shape Kepware's driver returns for an inert trigger write.
+        if (!AbCipSystemTagSource.IsTruthyRefresh(write.Value))
+            return new WriteResult(AbCipStatusMapper.Good);
+
+        if (!_devices.ContainsKey(deviceHost))
+            return new WriteResult(AbCipStatusMapper.BadNodeIdUnknown);
+
+        var builder = _cachedBuilder;
+        if (builder is null)
+        {
+            // Refresh fired before discovery had a chance to cache the builder — bump the
+            // counter (so operators can correlate the click with the lack of effect) but
+            // skip the dispatch since RebrowseAsync needs a builder to stream nodes into.
+            _systemTagSource.RecordRefreshTrigger(deviceHost);
+            return new WriteResult(AbCipStatusMapper.Good);
+        }
+
+        try
+        {
+            await RebrowseAsync(builder, cancellationToken).ConfigureAwait(false);
+            _systemTagSource.RecordRefreshTrigger(deviceHost);
+            return new WriteResult(AbCipStatusMapper.Good);
+        }
+        catch (OperationCanceledException)
+        {
+            throw;
+        }
+        catch (Exception ex)
+        {
+            _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead,
+                $"_RefreshTagDb dispatch failed: {ex.Message}");
+            return new WriteResult(AbCipStatusMapper.BadCommunicationError);
+        }
+    }
+
     /// <summary>
     ///     Execute one packable write — encode the value into the per-tag runtime, flush, and
     ///     map the resulting libplctag status. Exception-to-StatusCode mapping mirrors the
@@ -1652,6 +1755,8 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
     {
         ["AbCip.WritesSuppressed"] = _writeCoalescer.TotalWritesSuppressed,
         ["AbCip.WritesPassedThrough"] = _writeCoalescer.TotalWritesPassedThrough,
+        // PR abcip-4.4 — total _RefreshTagDb truthy writes that dispatched to RebrowseAsync.
+        ["AbCip.RefreshTriggers"] = _systemTagSource.TotalRefreshTriggers,
     };
 
     /// <summary>
@@ -1722,6 +1827,12 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
 
     private async Task DiscoverCoreAsync(IAddressSpaceBuilder builder, CancellationToken cancellationToken)
     {
+        // PR abcip-4.4 — remember the most-recent builder so a subsequent _RefreshTagDb
+        // write can hand it back to RebrowseAsync without a callback through Core. The
+        // IAddressSpaceBuilder contract documents that builders are reusable for the
+        // lifetime of the address space + the host owns the lifecycle, so caching the
+        // reference here is safe.
+        _cachedBuilder = builder;
         var root = builder.Folder("AbCip", "AbCip");
 
         foreach (var device in _options.Devices)
@@ -1841,25 +1952,29 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
     }
 
     /// <summary>
-    ///     PR abcip-4.3 — emit the per-device <c>_System</c> folder + its five read-only
+    ///     PR abcip-4.3 — emit the per-device <c>_System</c> folder + its diagnostic
-    ///     diagnostic variables. The <c>FullName</c> on each variable encodes the owning
+    ///     variables. PR abcip-4.4 added <c>_RefreshTagDb</c> as the sixth writeable entry.
-    ///     device's host address (<c>_System/&lt;host&gt;/&lt;name&gt;</c>) so the read path
+    ///     The <c>FullName</c> on each variable encodes the owning device's host address
-    ///     can route to <see cref="AbCipSystemTagSource.TryRead"/> without a separate
+    ///     (<c>_System/&lt;host&gt;/&lt;name&gt;</c>) so the read path can route to
-    ///     registry. Names + types stay in lockstep with
+    ///     <see cref="AbCipSystemTagSource.TryRead"/> without a separate registry. Names +
-    ///     <see cref="AbCipSystemTagSource.SystemTagNames"/>.
+    ///     types stay in lockstep with <see cref="AbCipSystemTagSource.SystemTagNames"/>.
     /// </summary>
     private static void EmitSystemTagFolder(IAddressSpaceBuilder deviceFolder, string deviceHostAddress)
     {
         var systemFolder = deviceFolder.Folder("_System", "_System");
-        EmitSystemVariable(systemFolder, deviceHostAddress, "_ConnectionStatus", DriverDataType.String);
+        EmitSystemVariable(systemFolder, deviceHostAddress, "_ConnectionStatus", DriverDataType.String, writeable: false);
-        EmitSystemVariable(systemFolder, deviceHostAddress, "_ScanRate", DriverDataType.Float64);
+        EmitSystemVariable(systemFolder, deviceHostAddress, "_ScanRate", DriverDataType.Float64, writeable: false);
-        EmitSystemVariable(systemFolder, deviceHostAddress, "_TagCount", DriverDataType.Int32);
+        EmitSystemVariable(systemFolder, deviceHostAddress, "_TagCount", DriverDataType.Int32, writeable: false);
-        EmitSystemVariable(systemFolder, deviceHostAddress, "_DeviceError", DriverDataType.String);
+        EmitSystemVariable(systemFolder, deviceHostAddress, "_DeviceError", DriverDataType.String, writeable: false);
-        EmitSystemVariable(systemFolder, deviceHostAddress, "_LastScanTimeMs", DriverDataType.Float64);
+        EmitSystemVariable(systemFolder, deviceHostAddress, "_LastScanTimeMs", DriverDataType.Float64, writeable: false);
+        // PR abcip-4.4 — Kepware-style writeable refresh trigger. Reads return false; a
+        // truthy write dispatches to RebrowseAsync via the cached IAddressSpaceBuilder.
+        EmitSystemVariable(systemFolder, deviceHostAddress, AbCipSystemTagSource.RefreshTagDbName,
+            DriverDataType.Boolean, writeable: true);
     }
 
     private static void EmitSystemVariable(
-        IAddressSpaceBuilder systemFolder, string deviceHostAddress, string name, DriverDataType type)
+        IAddressSpaceBuilder systemFolder, string deviceHostAddress, string name, DriverDataType type, bool writeable)
     {
         var fullName = $"{AbCipSystemTagSource.SystemFolderPrefix}{deviceHostAddress}/{name}";
         systemFolder.Variable(name, name, new DriverAttributeInfo(
@@ -1867,11 +1982,15 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
             DriverDataType: type,
             IsArray: false,
             ArrayDim: null,
-            // Read-only for now — PR abcip-4.4 will flip _RefreshTagDb to Operate when the
+            // PR abcip-4.4 — _RefreshTagDb is the only writeable entry; everything else
-            // refresh trigger lands. Today the AbCip system folder has no writeable members.
+            // remains ViewOnly so subscribed clients can't accidentally write the
-            SecurityClass: SecurityClassification.ViewOnly,
+            // diagnostic surface from a misbehaving SCADA template.
+            SecurityClass: writeable ? SecurityClassification.Operate : SecurityClassification.ViewOnly,
             IsHistorized: false,
             IsAlarm: false,
+            // _RefreshTagDb is idempotent in spirit (writing true twice is the same as
+            // once — both fire one rebrowse) but Kepware-style triggers don't deduplicate
+            // because operators expect each click to issue a fresh refresh.
             WriteIdempotent: false,
             Description: name switch
             {
@@ -1880,6 +1999,8 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
                 "_TagCount" => "Count of discovered tags on this device, excluding _System.",
                 "_DeviceError" => "Most recent driver-error message; empty when the device is healthy.",
                 "_LastScanTimeMs" => "Wall-clock duration of the most recent ReadAsync iteration on this device, in milliseconds.",
+                AbCipSystemTagSource.RefreshTagDbName =>
+                    "Writeable Kepware-style refresh trigger. Reads always return false. Writing a truthy value (true / non-zero / \"true\" / \"1\") forces a controller-side @tags re-walk via RebrowseAsync.",
                 _ => null,
             }));
     }

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipSystemTagSource.cs

@@ -10,11 +10,12 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip;
 ///     <see cref="IHostConnectivityProbe"/> + <see cref="DriverHealth"/> surfaces.
 /// </summary>
 /// <remarks>
-///     <para>Design parity with Modbus' <c>ModbusSystemTags</c> — the same five canonical
+///     <para>Design parity with Modbus' <c>ModbusSystemTags</c> — the same six canonical
 ///     names are exposed under each device's <c>_System</c> folder so the Admin UI / SCADA
 ///     clients can pivot from "is the wire up?" to "what's our scan rate / tag count?"
-///     without leaving the OPC UA address space. PR 4.4 will turn <c>_RefreshTagDb</c>
+///     without leaving the OPC UA address space. PR 4.4 turns <c>_RefreshTagDb</c> into a
-///     into a writeable refresh trigger; everything 4.3 ships is read-only.</para>
+///     writeable Kepware-style trigger — reads always return <c>false</c>, writes of any
+///     truthy value dispatch to <see cref="AbCipDriver.RebrowseAsync"/>.</para>
 ///     <list type="bullet">
 ///         <item><c>_ConnectionStatus</c> — string, mirrors the device's <see cref="HostState"/>.</item>
 ///         <item><c>_ScanRate</c> — double, the configured probe interval in milliseconds
@@ -24,10 +25,21 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip;
 ///         <item><c>_DeviceError</c> — string, the most recent driver-error message or empty.</item>
 ///         <item><c>_LastScanTimeMs</c> — double, wall-clock ms of the last poll-loop
 ///         iteration on this device.</item>
+///         <item><c>_RefreshTagDb</c> — boolean, writeable Kepware-style trigger. Reads
+///         always return <c>false</c>; writing any truthy value (true / non-zero / "true"
+///         / "1") forces a controller-side re-walk via
+///         <see cref="AbCipDriver.RebrowseAsync"/>.</item>
 ///     </list>
 /// </remarks>
 public sealed class AbCipSystemTagSource
 {
+    /// <summary>
+    ///     PR abcip-4.4 — the writeable Kepware-style refresh-trigger system tag. Reads
+    ///     always return <c>false</c>; writes of any truthy value cause the driver to
+    ///     re-run discovery against the live controller symbol table.
+    /// </summary>
+    public const string RefreshTagDbName = "_RefreshTagDb";
+
     /// <summary>Canonical names the system folder exposes — keep in lockstep with discovery.</summary>
     public static readonly IReadOnlyList<string> SystemTagNames =
     [
@@ -36,6 +48,7 @@ public sealed class AbCipSystemTagSource
         "_TagCount",
         "_DeviceError",
         "_LastScanTimeMs",
+        RefreshTagDbName,
     ];
 
     /// <summary>
@@ -48,8 +61,49 @@ public sealed class AbCipSystemTagSource
 
     private readonly Dictionary<string, SystemTagSnapshot> _snapshots =
         new(StringComparer.OrdinalIgnoreCase);
+    private readonly Dictionary<string, long> _refreshTriggers =
+        new(StringComparer.OrdinalIgnoreCase);
+    private long _totalRefreshTriggers;
     private readonly object _lock = new();
 
+    /// <summary>
+    ///     PR abcip-4.4 — total <c>_RefreshTagDb</c> writes across every device managed by
+    ///     the driver. Surfaced through <see cref="AbCipDriver.GetHealth"/> as the
+    ///     <c>AbCip.RefreshTriggers</c> diagnostic counter.
+    /// </summary>
+    public long TotalRefreshTriggers => Interlocked.Read(ref _totalRefreshTriggers);
+
+    /// <summary>
+    ///     PR abcip-4.4 — number of times <c>_RefreshTagDb</c> has been written for this
+    ///     specific device. Returns <c>0</c> when the device has never seen a refresh
+    ///     write (or isn't known to the source).
+    /// </summary>
+    public long GetRefreshTriggerCount(string deviceHostAddress)
+    {
+        ArgumentNullException.ThrowIfNull(deviceHostAddress);
+        lock (_lock)
+        {
+            return _refreshTriggers.TryGetValue(deviceHostAddress, out var n) ? n : 0;
+        }
+    }
+
+    /// <summary>
+    ///     PR abcip-4.4 — bump the per-device + global refresh counters for a successful
+    ///     <c>_RefreshTagDb</c> write. Called from <see cref="AbCipDriver.WriteAsync"/>
+    ///     after the rebrowse dispatch lands so a failed dispatch doesn't pollute the
+    ///     counter.
+    /// </summary>
+    public void RecordRefreshTrigger(string deviceHostAddress)
+    {
+        ArgumentNullException.ThrowIfNull(deviceHostAddress);
+        Interlocked.Increment(ref _totalRefreshTriggers);
+        lock (_lock)
+        {
+            _refreshTriggers[deviceHostAddress] =
+                (_refreshTriggers.TryGetValue(deviceHostAddress, out var n) ? n : 0) + 1;
+        }
+    }
+
     /// <summary>
     ///     Replace the snapshot for one device. Called on every health transition + every
     ///     successful read iteration so the surfaced values track the live driver loop
@@ -112,6 +166,15 @@ public sealed class AbCipSystemTagSource
             return false;
         }
 
+        // PR abcip-4.4 — _RefreshTagDb is a Kepware-style writeable trigger: reads always
+        // return false (the trigger latches back to "idle" the moment the dispatch returns)
+        // so subscribed clients see a stable shape regardless of how many refreshes fired.
+        if (string.Equals(name, RefreshTagDbName, StringComparison.Ordinal))
+        {
+            value = false;
+            return true;
+        }
+
         var snapshot = TryGet(deviceHostAddress);
         if (snapshot is null)
         {
@@ -139,6 +202,51 @@ public sealed class AbCipSystemTagSource
         return true;
     }
 
+    /// <summary>
+    ///     PR abcip-4.4 — recognise <c>_RefreshTagDb</c> writes. Accepts both bare
+    ///     (<c>_RefreshTagDb</c>) + prefixed (<c>_System/_RefreshTagDb</c>) shapes so
+    ///     callers can pass whichever form the address came in as.
+    /// </summary>
+    public static bool IsRefreshTagDb(string addressUnderSystem)
+    {
+        if (string.IsNullOrEmpty(addressUnderSystem)) return false;
+        var name = addressUnderSystem.StartsWith(SystemFolderPrefix, StringComparison.Ordinal)
+            ? addressUnderSystem[SystemFolderPrefix.Length..]
+            : addressUnderSystem;
+        return string.Equals(name, RefreshTagDbName, StringComparison.Ordinal);
+    }
+
+    /// <summary>
+    ///     PR abcip-4.4 — Kepware-style truthy coercion for the <c>_RefreshTagDb</c> trigger.
+    ///     Mirrors the same wire-format the OPC UA stack delivers: booleans pass through;
+    ///     integers / doubles trigger when non-zero; strings parse as <c>"true"</c> /
+    ///     <c>"1"</c> (case-insensitive). Anything else (null, empty, an unparseable string)
+    ///     is treated as <c>false</c> + the write becomes a no-op.
+    /// </summary>
+    public static bool IsTruthyRefresh(object? value)
+    {
+        if (value is null) return false;
+        return value switch
+        {
+            bool b => b,
+            sbyte s => s != 0,
+            byte b => b != 0,
+            short s => s != 0,
+            ushort u => u != 0,
+            int i => i != 0,
+            uint u => u != 0,
+            long l => l != 0,
+            ulong u => u != 0,
+            float f => f != 0f && !float.IsNaN(f),
+            double d => d != 0.0 && !double.IsNaN(d),
+            decimal m => m != 0m,
+            string s => bool.TryParse(s, out var parsed)
+                ? parsed
+                : (int.TryParse(s, out var n) && n != 0),
+            _ => false,
+        };
+    }
+
     /// <summary>
     ///     <c>true</c> when <paramref name="reference"/> targets a node under the synthetic
     ///     <c>_System/</c> folder. The driver's read path uses this to bypass the libplctag

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/AbCipRefreshTagDbTests.cs

@@ -0,0 +1,91 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.AbCip;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests;
+
+/// <summary>
+///     PR abcip-4.4 — end-to-end coverage that writing <c>_RefreshTagDb</c> on the
+///     synthetic system folder dispatches to <see cref="AbCipDriver.RebrowseAsync"/>
+///     against a live <c>ab_server</c>. Mirrors <see cref="AbCipSystemTagDiscoveryTests"/>
+///     but exercises the write entry point so the same outcome (template cache cleared,
+///     enumerator re-walked) is observable through the OPC UA write surface.
+/// </summary>
+[Trait("Category", "Integration")]
+[Trait("Requires", "AbServer")]
+public sealed class AbCipRefreshTagDbTests
+{
+    [AbServerFact]
+    public async Task RefreshTagDb_write_invokes_rebrowse_and_bumps_counter()
+    {
+        var profile = KnownProfiles.ControlLogix;
+        var fixture = new AbServerFixture(profile);
+        await fixture.InitializeAsync();
+        try
+        {
+            var deviceUri = $"ab://127.0.0.1:{fixture.Port}/1,0";
+            var drv = new AbCipDriver(new AbCipDriverOptions
+            {
+                Devices = [new AbCipDeviceOptions(deviceUri, profile.Family)],
+                Tags = [new AbCipTagDefinition("Counter", deviceUri, "TestDINT", AbCipDataType.DInt)],
+                EnableControllerBrowse = true,
+                Timeout = TimeSpan.FromSeconds(5),
+            }, "drv-refresh-tagdb");
+
+            await drv.InitializeAsync("{}", CancellationToken.None);
+
+            // Discovery primes the cached builder so the subsequent _RefreshTagDb write
+            // has a target to dispatch to. The same fixture pattern from AbCipRebrowseTests
+            // is exercised here through the write surface instead of a direct
+            // RebrowseAsync call.
+            var builder = new RecordingBuilder();
+            await drv.DiscoverAsync(builder, CancellationToken.None);
+
+            // Seed the template cache so we can assert RebrowseAsync clears it — same
+            // behavioural contract as the unit test, validated against a live walker.
+            drv.TemplateCache.Put(deviceUri, 42, new AbCipUdtShape("T", 4, []));
+            drv.TemplateCache.Count.ShouldBe(1);
+
+            var refreshRef = $"_System/{deviceUri}/{AbCipSystemTagSource.RefreshTagDbName}";
+            var results = await drv.WriteAsync(
+                [new WriteRequest(refreshRef, true)], CancellationToken.None);
+
+            results[0].StatusCode.ShouldBe(AbCipStatusMapper.Good);
+            // RebrowseAsync drops the template cache + the diagnostics counter advances.
+            drv.TemplateCache.Count.ShouldBe(0);
+            drv.SystemTagSource.GetRefreshTriggerCount(deviceUri).ShouldBe(1);
+            drv.GetHealth().DiagnosticsOrEmpty["AbCip.RefreshTriggers"].ShouldBe(1);
+
+            await drv.ShutdownAsync(CancellationToken.None);
+        }
+        finally
+        {
+            await fixture.DisposeAsync();
+        }
+    }
+
+    private sealed class RecordingBuilder : IAddressSpaceBuilder
+    {
+        public List<(string BrowseName, string DisplayName)> Folders { get; } = new();
+        public List<(string BrowseName, DriverAttributeInfo Info)> Variables { get; } = new();
+
+        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 _, DriverDataType __, object? ___) { }
+
+        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) { }
+        }
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipRefreshTagDbTests.cs

@@ -0,0 +1,376 @@
+using System.Runtime.CompilerServices;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.AbCip;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests;
+
+/// <summary>
+///     PR abcip-4.4 — coverage for the writeable <c>_RefreshTagDb</c> system tag. Discovery
+///     emits the entry as Operate, reads always return <c>false</c>, and writes of any
+///     truthy value dispatch to <see cref="AbCipDriver.RebrowseAsync"/> while bumping the
+///     <c>AbCip.RefreshTriggers</c> diagnostic counter. Falsy / unparseable writes are
+///     no-ops so a SCADA template that pulses the trigger off after firing it doesn't see
+///     a phantom error.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class AbCipRefreshTagDbTests
+{
+    private const string Host = "ab://10.0.0.5/1,0";
+    private static string RefreshRef(string host = Host) =>
+        $"_System/{host}/{AbCipSystemTagSource.RefreshTagDbName}";
+
+    [Fact]
+    public async Task Discovery_emits_RefreshTagDb_as_writeable()
+    {
+        var builder = new RecordingBuilder();
+        await using var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Host)],
+            Probe = new AbCipProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.DiscoverAsync(builder, CancellationToken.None);
+
+        var refreshVar = builder.Variables.Single(v => v.Info.FullName.EndsWith("/_RefreshTagDb"));
+        refreshVar.Info.SecurityClass.ShouldBe(SecurityClassification.Operate);
+        refreshVar.Info.DriverDataType.ShouldBe(DriverDataType.Boolean);
+        refreshVar.Info.FullName.ShouldBe($"_System/{Host}/_RefreshTagDb");
+    }
+
+    [Fact]
+    public async Task Read_RefreshTagDb_returns_false()
+    {
+        await using var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Host)],
+            Probe = new AbCipProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var snaps = await drv.ReadAsync([RefreshRef()], CancellationToken.None);
+
+        snaps[0].StatusCode.ShouldBe(AbCipStatusMapper.Good);
+        snaps[0].Value.ShouldBe(false);
+    }
+
+    [Fact]
+    public async Task Read_RefreshTagDb_returns_false_after_truthy_write()
+    {
+        // Writing the trigger doesn't change the read shape — it's always false the next
+        // time a client reads it (Kepware-style "latches back to idle" semantics).
+        var factory = new CountingEnumeratorFactory();
+        await using var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Host)],
+            EnableControllerBrowse = true,
+            Probe = new AbCipProbeOptions { Enabled = false },
+        }, "drv-1", enumeratorFactory: factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await drv.DiscoverAsync(new RecordingBuilder(), CancellationToken.None);
+
+        await drv.WriteAsync([new WriteRequest(RefreshRef(), true)], CancellationToken.None);
+
+        var snaps = await drv.ReadAsync([RefreshRef()], CancellationToken.None);
+        snaps[0].StatusCode.ShouldBe(AbCipStatusMapper.Good);
+        snaps[0].Value.ShouldBe(false);
+    }
+
+    [Fact]
+    public async Task Truthy_write_dispatches_to_RebrowseAsync()
+    {
+        var factory = new CountingEnumeratorFactory(
+            new AbCipDiscoveredTag("Pressure", null, AbCipDataType.Real, ReadOnly: false));
+        await using var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Host)],
+            EnableControllerBrowse = true,
+            Probe = new AbCipProbeOptions { Enabled = false },
+        }, "drv-1", enumeratorFactory: factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        // First DiscoverAsync caches the builder + bumps the enumerator once.
+        await drv.DiscoverAsync(new RecordingBuilder(), CancellationToken.None);
+        factory.EnumerationCount.ShouldBe(1);
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest(RefreshRef(), true)], CancellationToken.None);
+
+        results[0].StatusCode.ShouldBe(AbCipStatusMapper.Good);
+        // RebrowseAsync re-runs the enumerator → count bumps.
+        factory.EnumerationCount.ShouldBe(2);
+    }
+
+    [Theory]
+    [InlineData(true)]
+    [InlineData(1)]
+    [InlineData(1.5)]
+    [InlineData("true")]
+    [InlineData("True")]
+    [InlineData("1")]
+    public async Task Various_truthy_shapes_all_trigger_a_refresh(object value)
+    {
+        var factory = new CountingEnumeratorFactory();
+        await using var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Host)],
+            EnableControllerBrowse = true,
+            Probe = new AbCipProbeOptions { Enabled = false },
+        }, "drv-1", enumeratorFactory: factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await drv.DiscoverAsync(new RecordingBuilder(), CancellationToken.None);
+        var baseline = factory.EnumerationCount;
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest(RefreshRef(), value)], CancellationToken.None);
+
+        results[0].StatusCode.ShouldBe(AbCipStatusMapper.Good);
+        factory.EnumerationCount.ShouldBe(baseline + 1);
+    }
+
+    [Theory]
+    [InlineData(false)]
+    [InlineData(0)]
+    [InlineData(0.0)]
+    [InlineData("false")]
+    [InlineData("False")]
+    [InlineData("0")]
+    [InlineData("")]
+    [InlineData("not-a-bool")]
+    public async Task Falsy_or_unparseable_write_is_a_noop(object value)
+    {
+        var factory = new CountingEnumeratorFactory();
+        await using var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Host)],
+            EnableControllerBrowse = true,
+            Probe = new AbCipProbeOptions { Enabled = false },
+        }, "drv-1", enumeratorFactory: factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await drv.DiscoverAsync(new RecordingBuilder(), CancellationToken.None);
+        var baseline = factory.EnumerationCount;
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest(RefreshRef(), value)], CancellationToken.None);
+
+        results[0].StatusCode.ShouldBe(AbCipStatusMapper.Good);
+        factory.EnumerationCount.ShouldBe(baseline);
+        drv.SystemTagSource.GetRefreshTriggerCount(Host).ShouldBe(0);
+    }
+
+    [Fact]
+    public async Task Null_write_is_a_noop()
+    {
+        var factory = new CountingEnumeratorFactory();
+        await using var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Host)],
+            EnableControllerBrowse = true,
+            Probe = new AbCipProbeOptions { Enabled = false },
+        }, "drv-1", enumeratorFactory: factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await drv.DiscoverAsync(new RecordingBuilder(), CancellationToken.None);
+        var baseline = factory.EnumerationCount;
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest(RefreshRef(), null)], CancellationToken.None);
+
+        results[0].StatusCode.ShouldBe(AbCipStatusMapper.Good);
+        factory.EnumerationCount.ShouldBe(baseline);
+    }
+
+    [Fact]
+    public async Task RefreshTriggers_counter_bumps_per_truthy_write()
+    {
+        var factory = new CountingEnumeratorFactory();
+        await using var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Host)],
+            EnableControllerBrowse = true,
+            Probe = new AbCipProbeOptions { Enabled = false },
+        }, "drv-1", enumeratorFactory: factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await drv.DiscoverAsync(new RecordingBuilder(), CancellationToken.None);
+
+        await drv.WriteAsync([new WriteRequest(RefreshRef(), true)], CancellationToken.None);
+        await drv.WriteAsync([new WriteRequest(RefreshRef(), true)], CancellationToken.None);
+        await drv.WriteAsync([new WriteRequest(RefreshRef(), false)], CancellationToken.None);
+
+        drv.GetHealth().DiagnosticsOrEmpty["AbCip.RefreshTriggers"].ShouldBe(2);
+        drv.SystemTagSource.GetRefreshTriggerCount(Host).ShouldBe(2);
+        drv.SystemTagSource.TotalRefreshTriggers.ShouldBe(2);
+    }
+
+    [Fact]
+    public async Task Two_devices_keep_independent_refresh_counters()
+    {
+        const string a = "ab://10.0.0.5/1,0";
+        const string b = "ab://10.0.0.6/1,0";
+        var factory = new CountingEnumeratorFactory();
+        await using var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(a), new AbCipDeviceOptions(b)],
+            EnableControllerBrowse = true,
+            Probe = new AbCipProbeOptions { Enabled = false },
+        }, "drv-1", enumeratorFactory: factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await drv.DiscoverAsync(new RecordingBuilder(), CancellationToken.None);
+
+        await drv.WriteAsync(
+            [new WriteRequest($"_System/{a}/_RefreshTagDb", true)], CancellationToken.None);
+        await drv.WriteAsync(
+            [new WriteRequest($"_System/{b}/_RefreshTagDb", true)], CancellationToken.None);
+        await drv.WriteAsync(
+            [new WriteRequest($"_System/{a}/_RefreshTagDb", true)], CancellationToken.None);
+
+        drv.SystemTagSource.GetRefreshTriggerCount(a).ShouldBe(2);
+        drv.SystemTagSource.GetRefreshTriggerCount(b).ShouldBe(1);
+        drv.SystemTagSource.TotalRefreshTriggers.ShouldBe(3);
+    }
+
+    [Fact]
+    public async Task Write_to_unknown_System_name_returns_BadNotWritable()
+    {
+        await using var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Host)],
+            Probe = new AbCipProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await drv.DiscoverAsync(new RecordingBuilder(), CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest($"_System/{Host}/_ConnectionStatus", "Running")],
+            CancellationToken.None);
+
+        results[0].StatusCode.ShouldBe(AbCipStatusMapper.BadNotWritable);
+    }
+
+    [Fact]
+    public async Task Write_to_unknown_System_device_returns_BadNodeIdUnknown()
+    {
+        await using var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Host)],
+            Probe = new AbCipProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await drv.DiscoverAsync(new RecordingBuilder(), CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("_System/ab://10.99.99.99/1,0/_RefreshTagDb", true)],
+            CancellationToken.None);
+
+        results[0].StatusCode.ShouldBe(AbCipStatusMapper.BadNodeIdUnknown);
+    }
+
+    [Fact]
+    public async Task Refresh_write_before_discovery_is_a_noop_Good()
+    {
+        // _cachedBuilder is null before DiscoverAsync runs — the write should still report
+        // Good (Kepware-style trigger semantics never bubble "no address space yet" up to
+        // the OPC UA client) but not invoke RebrowseAsync.
+        var factory = new CountingEnumeratorFactory();
+        await using var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Host)],
+            EnableControllerBrowse = true,
+            Probe = new AbCipProbeOptions { Enabled = false },
+        }, "drv-1", enumeratorFactory: factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest(RefreshRef(), true)], CancellationToken.None);
+
+        results[0].StatusCode.ShouldBe(AbCipStatusMapper.Good);
+        factory.EnumerationCount.ShouldBe(0);
+    }
+
+    [Fact]
+    public async Task System_writes_do_not_block_genuine_tag_writes_in_the_same_batch()
+    {
+        // Mixed batch: one _RefreshTagDb + one ordinary tag write. The system entry is
+        // intercepted before the planner runs, the ordinary entry still flows through
+        // multi-write packing untouched, and both results land at their original indices.
+        var factory = new CountingEnumeratorFactory();
+        var tagFactory = new FakeAbCipTagFactory
+        {
+            Customise = p => new FakeAbCipTag(p) { Status = 0 },
+        };
+        await using var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(Host)],
+            EnableControllerBrowse = true,
+            Tags = [new AbCipTagDefinition("Speed", Host, "Motor1.Speed", AbCipDataType.DInt)],
+            Probe = new AbCipProbeOptions { Enabled = false },
+        }, "drv-1", tagFactory: tagFactory, enumeratorFactory: factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await drv.DiscoverAsync(new RecordingBuilder(), CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+        [
+            new WriteRequest(RefreshRef(), true),
+            new WriteRequest("Speed", 42),
+        ], CancellationToken.None);
+
+        results[0].StatusCode.ShouldBe(AbCipStatusMapper.Good);
+        results[1].StatusCode.ShouldBe(AbCipStatusMapper.Good);
+        drv.SystemTagSource.GetRefreshTriggerCount(Host).ShouldBe(1);
+    }
+
+    // ---- helpers (mirror AbCipRebrowseTests) ----
+
+    private sealed class RecordingBuilder : IAddressSpaceBuilder
+    {
+        public List<(string BrowseName, string DisplayName)> Folders { get; } = new();
+        public List<(string BrowseName, DriverAttributeInfo Info)> Variables { get; } = new();
+
+        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 _, DriverDataType __, object? ___) { }
+
+        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) { }
+        }
+    }
+
+    private sealed class CountingEnumeratorFactory : IAbCipTagEnumeratorFactory
+    {
+        private readonly AbCipDiscoveredTag[] _tags;
+        public int CreateCount { get; private set; }
+        public int EnumerationCount { get; private set; }
+
+        public CountingEnumeratorFactory(params AbCipDiscoveredTag[] tags) => _tags = tags;
+
+        public IAbCipTagEnumerator Create()
+        {
+            CreateCount++;
+            return new CountingEnumerator(this);
+        }
+
+        private sealed class CountingEnumerator(CountingEnumeratorFactory outer) : IAbCipTagEnumerator
+        {
+            public async IAsyncEnumerable<AbCipDiscoveredTag> EnumerateAsync(
+                AbCipTagCreateParams deviceParams,
+                [EnumeratorCancellation] CancellationToken cancellationToken)
+            {
+                outer.EnumerationCount++;
+                await Task.CompletedTask;
+                foreach (var t in outer._tags) yield return t;
+            }
+            public void Dispose() { }
+        }
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipSystemTagSourceTests.cs

@@ -104,7 +104,7 @@ public sealed class AbCipSystemTagSourceTests
     }
 
     [Fact]
-    public async Task Discovery_emits_five_system_nodes_per_device()
+    public async Task Discovery_emits_six_system_nodes_per_device()
     {
         var builder = new RecordingBuilder();
         var drv = new AbCipDriver(new AbCipDriverOptions
@@ -122,19 +122,26 @@ public sealed class AbCipSystemTagSourceTests
             .Select(v => v.BrowseName)
             .OrderBy(s => s)
             .ToList();
+        // PR abcip-4.4 — _RefreshTagDb joins the original five.
         systemVars.ShouldBe(new[]
         {
             "_ConnectionStatus", "_DeviceError", "_LastScanTimeMs",
-            "_ScanRate", "_TagCount",
+            "_RefreshTagDb", "_ScanRate", "_TagCount",
         });
-        // All five carry the device host inside the FullName.
+        // All six carry the device host inside the FullName.
         builder.Variables
             .Where(v => v.Info.FullName.StartsWith("_System/"))
             .ShouldAllBe(v => v.Info.FullName.StartsWith("_System/ab://10.0.0.5/1,0/"));
-        // PR 4.4 will flip _RefreshTagDb to writeable; today every system var is ViewOnly.
+        // PR abcip-4.4 — _RefreshTagDb is the sole writeable entry (Operate); the rest
+        // remain ViewOnly so a SCADA template can't accidentally clobber the diagnostic
+        // surface.
         builder.Variables
-            .Where(v => v.Info.FullName.StartsWith("_System/"))
+            .Where(v => v.Info.FullName.StartsWith("_System/")
+                && !v.Info.FullName.EndsWith("/_RefreshTagDb"))
             .ShouldAllBe(v => v.Info.SecurityClass == SecurityClassification.ViewOnly);
+        builder.Variables
+            .Single(v => v.Info.FullName.EndsWith("/_RefreshTagDb"))
+            .Info.SecurityClass.ShouldBe(SecurityClassification.Operate);
     }
 
     [Fact]
@@ -155,7 +162,8 @@ public sealed class AbCipSystemTagSourceTests
         await drv.DiscoverAsync(builder, CancellationToken.None);
 
         builder.Folders.Count(f => f.BrowseName == "_System").ShouldBe(2);
-        builder.Variables.Count(v => v.Info.FullName.StartsWith("_System/")).ShouldBe(10);
+        // PR abcip-4.4 — six system variables per device (added _RefreshTagDb).
+        builder.Variables.Count(v => v.Info.FullName.StartsWith("_System/")).ShouldBe(12);
         builder.Variables
             .Where(v => v.Info.FullName.StartsWith("_System/"))
             .Select(v => v.Info.FullName)