File and fix Server-030 and Client.Dotnet-017 from e2e surfacing

Both findings surfaced when running the cross-language e2e matrix
(scripts/run-client-e2e-tests.ps1) against the redeployed gateway at
commit 84d36b7. Filed in code-reviews/Server/findings.md and
code-reviews/Client.Dotnet/findings.md and fixed in the same change.

Server-030 (Medium / Error handling): GatewaySession.GetReadyWorkerClient
gated on `_state == Ready && _workerClient.State == Ready` but only
formatted `_state` into the SessionManagerException message. Under load
the gateway-driven `_state` and the worker-driven `WorkerClient.State`
can diverge, producing a self-contradictory diagnostic ("Session ... is
not ready. Current state is Ready."). The Java e2e client hit this on
the 56th item after 55 successful add-items. Rewrote the message to
include both states ("Session state is X; worker state is Y"), added
an XML doc explaining the two-state contract and that this branch is
the fail-fast for a divergence race, and added regression test
SessionManagerTests.InvokeAsync_WhenWorkerNotReadyButSessionReady_DiagnosticIncludesBothStates
that pins both states appear in the message. The deeper race (should
the gateway briefly wait for worker-Ready before failing?) remains
open as a follow-up.

Client.Dotnet-017 (Low / Error handling): stream-events CLI threw
OperationCanceledException as an unhandled exception when the user's
--timeout expired before --max-events was reached. Exit code
-532462766, no aggregate JSON. The other client CLIs (Go, Rust, Python,
Java) exit 0 in this case. Wrapped the `await foreach` in
`catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)`
so the supplied token's cancellation (--timeout, Ctrl+C, or parent
CTS) becomes graceful completion; the aggregate `{ "events": [...] }`
JSON still runs after the catch. Added regression test
RunAsync_StreamEvents_WhenTimeoutFiresAfterEvents_EmitsCollectedEventsAndExitsZero
backed by a new FakeCliClient.StreamHangAfterEvents hook that yields
the configured events then parks on the cancellation token.

Side cleanup: the GatewayApplicationTests test added under Server-020
was asserting an invariant (`/dashboard/dashboard/X` doesn't exist)
that I broke by reverting Server-020 in 84d36b7. The doubled endpoint
shapes do exist now (MapGroup("/dashboard") prefixing an already
"/dashboard/X" @page directive) but they're harmless — no client
requests `/dashboard/dashboard/X`. Replaced the test with a positive
assertion (`/dashboard/X` routes ARE registered) and rewrote the XML
doc to record the actual contract.

Verified: dotnet test src/MxGateway.Tests passes 480/480, dotnet test
clients/dotnet/MxGateway.Client.Tests passes 77/77, gateway redeployed
at this commit and GET http://localhost:5130/dashboard returns 200.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

clients/dotnet/MxGateway.Client.Cli/MxGatewayClientCli.cs

@@ -1216,29 +1216,43 @@ public static class MxGatewayClientCli
             AfterWorkerSequence = arguments.GetUInt64("after-worker-sequence", 0),
         };
 
-        await foreach (MxEvent gatewayEvent in client.StreamEventsAsync(request, cancellationToken)
-            .WithCancellation(cancellationToken)
-            .ConfigureAwait(false))
+        try
         {
-            if (jsonLines)
+            await foreach (MxEvent gatewayEvent in client.StreamEventsAsync(request, cancellationToken)
+                .WithCancellation(cancellationToken)
+                .ConfigureAwait(false))
             {
-                output.WriteLine(ProtobufJsonFormatter.Format(gatewayEvent));
-            }
-            else if (json)
-            {
-                events.Add(gatewayEvent);
-            }
-            else
-            {
-                output.WriteLine(ProtobufJsonFormatter.Format(gatewayEvent));
-            }
+                if (jsonLines)
+                {
+                    output.WriteLine(ProtobufJsonFormatter.Format(gatewayEvent));
+                }
+                else if (json)
+                {
+                    events.Add(gatewayEvent);
+                }
+                else
+                {
+                    output.WriteLine(ProtobufJsonFormatter.Format(gatewayEvent));
+                }
 
-            eventCount++;
-            if (maxEvents > 0 && eventCount >= maxEvents)
-            {
-                break;
+                eventCount++;
+                if (maxEvents > 0 && eventCount >= maxEvents)
+                {
+                    break;
+                }
             }
         }
+        catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
+        {
+            // Client.Dotnet-017: the supplied cancellation token covers both the
+            // user's --timeout wall-clock budget (via CreateCancellation's
+            // CancelAfter) and external Ctrl+C / parent CTS cancellation. All
+            // three are graceful completion modes for a finite-window event
+            // collector: emit the events that arrived before the window closed
+            // and exit 0. The events list is well-formed at this point; the
+            // aggregate JSON below still runs. This matches how the Go, Rust,
+            // Python, and Java CLIs treat their equivalent timeouts.
+        }
 
         if (json && !jsonLines)
         {