fix(historian-gateway): cancellation-safe alarm writer + dispose-safe outbox + provisioner polish + outbox tests

I-1: GatewayAlarmHistorianWriter no longer dead-letters events cancelled
mid-drain at shutdown. WriteBatchAsync short-circuits remaining events to
RetryPlease once cancellation is requested, and SendOneAsync catches
OperationCanceledException (when the token is cancelled) -> RetryPlease,
so in-flight events stay queued instead of being permanently dropped.

I-2: FasterLogHistorizationOutbox.Dispose now guards the awaited periodic
loop with a broad catch (Exception) after the OperationCanceledException
catch, so a non-Faster teardown fault (e.g. ObjectDisposedException) can
never escape Dispose.

M-1: GatewayTagProvisioner skips the empty EnsureTags round-trip when every
request is non-historizable (early return).

M-2: GatewayTagProvisioner handles plain shutdown cancellation quietly
(Debug, not Warning), counting the unsent batch as Failed, never throwing.

M-3/M-4: Added remove-last-entry (TailAddress truncation branch) and
FIFO implicit-ack (RemoveAsync acks up to and including the target)
durability tests, both reopen-and-survive.

M-5: Clarifying comment in RecoverState on the transient over-capacity
rebuild after a crash between append-commit and drop-truncation-commit.

Claude-Session: https://claude.ai/code/session_012SDSQ3AcaXqPcBtDESBRii

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway.Tests/GatewayAlarmHistorianWriterTests.cs

@@ -174,6 +174,23 @@ public sealed class GatewayAlarmHistorianWriterTests
         Assert.Equal(HistorianWriteOutcome.PermanentFail, outcomes[0]);
     }
 
+    [Fact]
+    public async Task Cancellation_mid_drain_is_RetryPlease_not_PermanentFail()
+    {
+        // Shutdown mid-drain: a cancelled token must NOT dead-letter in-flight events (silent data
+        // loss). Every outcome is RetryPlease (stays queued for next startup), WriteBatchAsync never
+        // throws, and the gateway is not called with a cancelled token (short-circuited up front).
+        using var cts = new CancellationTokenSource();
+        await cts.CancelAsync();
+        var fake = new FakeHistorianGatewayClient { SendEventThrows = new OperationCanceledException() };
+
+        var outcomes = await Writer(fake).WriteBatchAsync(new[] { Evt("A"), Evt("B") }, cts.Token);
+
+        Assert.Equal(2, outcomes.Count);
+        Assert.All(outcomes, o => Assert.Equal(HistorianWriteOutcome.RetryPlease, o));
+        Assert.Equal(0, fake.SendEventCallCount);
+    }
+
     [Fact]
     public async Task Empty_batch_returns_empty()
     {