fix(focas): PMC coalescing treats any rc refusal as per-tag fallback, skips transient busy memo, one connect per batch (#266)

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe
2026-10-08 17:03:25 -04:00
parent 487d394cde
commit c86204b7d6
4 changed files with 99 additions and 21 deletions
@@ -132,6 +132,68 @@ public sealed class FocasPmcCoalescingDriverTests
        await drv.ShutdownAsync(CancellationToken.None);
    }

+    [Fact]
+    public async Task A_refusal_with_an_unmapped_rc_that_maps_to_BadCommunicationError_still_falls_back_per_tag()
+    {
+        var (drv, c) = await StartAsync(null,
+            Tag("A", "R100", FocasDataType.Byte), Tag("B", "R101", FocasDataType.Byte));
+        c.PmcRangeRejectors.Add((_, _, _) => true);
+        c.PmcRangeRejectStatus = FocasStatusMapper.BadCommunicationError;   // what an unlisted rc / EW_PARITY / EW_SOCKET maps to
+        c.Values["R100"] = (sbyte)1; c.Values["R101"] = (sbyte)2;
+
+        var r = await drv.ReadAsync(["A", "B"], CancellationToken.None);
+        r.Select(s => s.Value).ShouldBe([(object)(sbyte)1, (sbyte)2]);
+        r.ShouldAllBe(s => s.StatusCode == FocasStatusMapper.Good);
+
+        await drv.ReadAsync(["A", "B"], CancellationToken.None);
+        c.PmcRangeReads.Count.ShouldBe(1, "a deterministic rc refusal is memoised");
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task A_transient_busy_refusal_is_not_memoised()
+    {
+        var (drv, c) = await StartAsync(null,
+            Tag("A", "R100", FocasDataType.Byte), Tag("B", "R101", FocasDataType.Byte));
+        var busy = true;
+        c.PmcRangeRejectors.Add((_, _, _) => busy);
+        c.PmcRangeRejectStatus = FocasStatusMapper.BadDeviceFailure;        // EW_BUSY
+        c.Values["R100"] = (sbyte)1; c.Values["R101"] = (sbyte)2;
+
+        (await drv.ReadAsync(["A", "B"], CancellationToken.None)).ShouldAllBe(s => s.StatusCode == FocasStatusMapper.Good);
+        busy = false;
+        c.PmcMemory[("R", 100)] = 5; c.PmcMemory[("R", 101)] = 6;
+        var r = await drv.ReadAsync(["A", "B"], CancellationToken.None);
+
+        c.PmcRangeReads.Count.ShouldBe(2, "the range is retried once the CNC is no longer busy");
+        r.Select(s => s.Value).ShouldBe([(object)(sbyte)5, (sbyte)6]);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task A_down_device_costs_one_connect_attempt_per_batch_not_one_per_plan_and_tag()
+    {
+        var client = new FakeFocasClient { ThrowOnConnect = true };
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions(Host)],
+            Probe = new FocasProbeOptions { Enabled = false },
+            RawTags = FocasRawTags.Entries(new[]
+            {
+                Tag("A", "R100", FocasDataType.Byte), Tag("B", "R101", FocasDataType.Byte),
+                Tag("C", "R900", FocasDataType.Byte), Tag("D", "R2000", FocasDataType.Byte),
+            }),
+        }, "drv-1", new FakeFocasClientFactory { Customise = () => client });
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        var before = client.ConnectCount;
+
+        var r = await drv.ReadAsync(["A", "B", "C", "D"], CancellationToken.None);
+
+        r.ShouldAllBe(s => s.StatusCode == FocasStatusMapper.BadCommunicationError);
+        (client.ConnectCount - before).ShouldBe(1);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
    [Fact]
    public async Task A_transport_failure_fails_every_member_without_per_tag_retries()
    {