fix(vtags): real script timeout + ALC-safe compile cache (arch-review 02/U2,U3)

U2 (Critical): RoslynVirtualTagEvaluator ran scripts with a CancellationToken
that a synchronous Roslyn script can never observe, so one CPU-bound/infinite-
loop virtual-tag script hung the owning VirtualTagActor forever (no timeout, no
recovery). Route evaluation through the existing TimedScriptEvaluator (Task.Run
+ WaitAsync) so the wall-clock budget is real; a runaway script now returns Bad
within the timeout instead of wedging the actor.

U3 (High): the live path cached evaluators in a raw ConcurrentDictionary never
cleared on republish, leaking a collectible AssemblyLoadContext per edited
script forever. Swap in the purpose-built CompiledScriptCache (Lazy single-
compile, dispose-on-Clear) and add an apply-boundary clear: a new narrow
IScriptCacheOwner seam the VirtualTagHostActor calls on each ApplyVirtualTags
generation (mirrors ScriptedAlarmEngine's per-generation clear).

Tests: infinite-loop-fails-within-timeout (bounded by WaitAsync so a regression
fails instead of hanging), happy-path-after-wrapping, ClearCompiledScripts-
empties-cache, and a host-actor wiring guard asserting each apply generation
calls ClearCompiledScripts (theme #1 production-caller assertion). Host.Integration
VT suite 18/18, Runtime VT suite 12/12.

tests/Server/ZB.MOM.WW.OtOpcUa.Host.IntegrationTests/RoslynVirtualTagEvaluatorTests.cs

@@ -251,7 +251,7 @@ public sealed class RoslynVirtualTagEvaluatorTests
     }
 
     /// <summary>Decisive proof the fast-path skips Roslyn: the compiled-script cache (which every
-    /// Roslyn evaluation populates via <c>GetOrAdd</c>) stays EMPTY after a mirror evaluation, then
+    /// Roslyn evaluation populates via <c>GetOrCompile</c>) stays EMPTY after a mirror evaluation, then
     /// grows to one entry once a genuine (non-mirror) expression forces compilation.</summary>
     [Fact]
     public void Passthrough_does_not_populate_the_compiled_script_cache()
@@ -299,13 +299,74 @@ public sealed class RoslynVirtualTagEvaluatorTests
         entry.VirtualTagId.ShouldBe("vt-log");
     }
 
-    /// <summary>Reads the count of the private compiled-script cache via reflection.</summary>
+    // ── U2 — production timeout must be REAL: a CPU-bound/infinite-loop script must fail within the
+    //    wall-clock budget, never hang the owning actor. The pre-fix CTS-only path could not interrupt
+    //    a synchronous Roslyn script, so this class of script wedged the VirtualTagActor forever. ──
+
+    /// <summary>An infinite-loop script returns Failure ("timed out") within the timeout budget instead
+    /// of hanging. The whole call is bounded by <c>WaitAsync</c> so a regression FAILS the test (with a
+    /// TimeoutException) rather than wedging the suite.</summary>
+    [Fact]
+    public async Task Evaluate_infinite_loop_script_fails_within_timeout_and_does_not_hang()
+    {
+        using var sut = new RoslynVirtualTagEvaluator(
+            NullLogger<RoslynVirtualTagEvaluator>.Instance, NoOpScriptRoot(), TimeSpan.FromMilliseconds(200));
+
+        var evalTask = Task.Run(
+            () => sut.Evaluate("vt-loop", "while(true){}return 0;", new Dictionary<string, object?>()),
+            TestContext.Current.CancellationToken);
+
+        var result = await evalTask.WaitAsync(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken);
+
+        result.Success.ShouldBeFalse();
+        result.Reason.ShouldNotBeNull();
+        result.Reason.ShouldContain("timed out");
+    }
+
+    /// <summary>Regression: routing through <see cref="TimedScriptEvaluator{TContext, TResult}"/> did not
+    /// break the happy path — a fast compiled script still returns its value well within the budget.</summary>
+    [Fact]
+    public void Evaluate_fast_script_still_returns_value_after_timeout_wrapping()
+    {
+        using var sut = new RoslynVirtualTagEvaluator(
+            NullLogger<RoslynVirtualTagEvaluator>.Instance, NoOpScriptRoot(), TimeSpan.FromMilliseconds(200));
+
+        var result = sut.Evaluate("vt-fast", "return (int)ctx.GetTag(\"a\").Value + 1;",
+            new Dictionary<string, object?> { ["a"] = 41 });
+
+        result.Success.ShouldBeTrue(result.Reason);
+        result.Value.ShouldBe(42);
+    }
+
+    // ── U3 — the apply-boundary clear (IScriptCacheOwner) drops compiled entries so their collectible
+    //    AssemblyLoadContexts are reclaimed. (The ALC-unload-on-Clear proof lives in CompiledScriptCacheTests;
+    //    here we assert the adapter's ClearCompiledScripts actually empties its cache.) ──
+
+    /// <summary>Verifies <see cref="RoslynVirtualTagEvaluator.ClearCompiledScripts"/> drops every cached
+    /// compile — the hook the host actor calls per deploy generation to release stale ALCs.</summary>
+    [Fact]
+    public void ClearCompiledScripts_empties_the_compile_cache()
+    {
+        using var sut = new RoslynVirtualTagEvaluator(NullLogger<RoslynVirtualTagEvaluator>.Instance, NoOpScriptRoot());
+
+        sut.Evaluate("vt-a", "return (int)ctx.GetTag(\"a\").Value + 1;", new Dictionary<string, object?> { ["a"] = 1 });
+        CompiledCacheCount(sut).ShouldBe(1);
+
+        sut.ClearCompiledScripts();
+
+        CompiledCacheCount(sut).ShouldBe(0);
+    }
+
+    /// <summary>Reads the count of the private compiled-script cache via reflection. The cache is a
+    /// <c>CompiledScriptCache&lt;,&gt;</c> which exposes a <c>Count</c> property (not <c>ICollection</c>).</summary>
     private static int CompiledCacheCount(RoslynVirtualTagEvaluator sut)
     {
         var field = typeof(RoslynVirtualTagEvaluator)
             .GetField("_cache", BindingFlags.Instance | BindingFlags.NonPublic);
         field.ShouldNotBeNull();
-        var cache = (ICollection)field.GetValue(sut)!;
-        return cache.Count;
+        var cache = field.GetValue(sut)!;
+        var countProp = cache.GetType().GetProperty("Count");
+        countProp.ShouldNotBeNull();
+        return (int)countProp.GetValue(cache)!;
     }
 }