fix(calculation): read cache carries real input status + timestamps

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationEvaluatorTests.cs

@@ -4,6 +4,7 @@ using Microsoft.Extensions.Logging.Abstractions;
 using Serilog;
 using Shouldly;
 using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 using ZB.MOM.WW.OtOpcUa.Core.Scripting;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests;
@@ -230,6 +231,74 @@ public sealed class CalculationEvaluatorTests
         return (int)countProp.GetValue(cache)!;
     }
 
+    // ── input quality reaches the script (archreview 05/STAB-19) ────────────────────────────
+
+    /// <summary>
+    ///     A script reading <c>ctx.GetTag(path).StatusCode</c> sees the input's <b>real</b> status.
+    ///     The read cache used to stamp every dependency Good, so a script that checked quality was lied
+    ///     to — and, since the driver now holds on Bad, an Uncertain input is precisely the case where a
+    ///     script can still make a qualified decision and needs the truth to do it.
+    /// </summary>
+    [Fact]
+    public void The_read_cache_carries_the_inputs_real_status_code()
+    {
+        const uint uncertain = 0x40000000u;
+        using var sut = new CalculationEvaluator(NullLogger<CalculationEvaluator>.Instance, NoOpScriptRoot());
+        var sourceStamp = new DateTime(2026, 8, 20, 9, 0, 0, DateTimeKind.Utc);
+
+        var result = sut.Evaluate(
+            calcTagId: "calc-quality",
+            scriptSource: "return (long)ctx.GetTag(\"a\").StatusCode;",
+            dependencies: new Dictionary<string, DataValueSnapshot>
+            {
+                ["a"] = new(7.0, uncertain, sourceStamp, sourceStamp),
+            });
+
+        result.Success.ShouldBeTrue(result.Reason);
+        result.Value.ShouldBe((long)uncertain);
+    }
+
+    /// <summary>
+    ///     The dependency's own source timestamp reaches the script too. The old cache stamped
+    ///     evaluation time on every input, so a script comparing input ages compared its own clock with
+    ///     itself.
+    /// </summary>
+    [Fact]
+    public void The_read_cache_carries_the_inputs_real_source_timestamp()
+    {
+        using var sut = new CalculationEvaluator(NullLogger<CalculationEvaluator>.Instance, NoOpScriptRoot());
+        var sourceStamp = new DateTime(2026, 8, 20, 9, 0, 0, DateTimeKind.Utc);
+
+        var result = sut.Evaluate(
+            calcTagId: "calc-stamp",
+            scriptSource: "return ctx.GetTag(\"a\").SourceTimestampUtc;",
+            dependencies: new Dictionary<string, DataValueSnapshot>
+            {
+                ["a"] = new(7.0, 0u, sourceStamp, DateTime.UtcNow),
+            });
+
+        result.Success.ShouldBeTrue(result.Reason);
+        result.Value.ShouldBe(sourceStamp);
+    }
+
+    /// <summary>The passthrough fast path takes the same snapshot input and returns its value.</summary>
+    [Fact]
+    public void The_passthrough_fast_path_accepts_snapshots()
+    {
+        using var sut = new CalculationEvaluator(NullLogger<CalculationEvaluator>.Instance, NoOpScriptRoot());
+
+        var result = sut.Evaluate(
+            calcTagId: "calc-mirror",
+            scriptSource: "return ctx.GetTag(\"a\").Value;",
+            dependencies: new Dictionary<string, DataValueSnapshot>
+            {
+                ["a"] = new(42, 0u, DateTime.UtcNow, DateTime.UtcNow),
+            });
+
+        result.Success.ShouldBeTrue(result.Reason);
+        result.Value.ShouldBe(42);
+    }
+
     /// <summary>Minimal <see cref="ILogger{T}"/> that records emitted entries so the SetVirtualTag-drop
     /// test can assert the Debug "dropped" line was logged.</summary>
     private sealed class CapturingLogger : ILogger<CalculationEvaluator>