Resolve Client.Java-006..012 code-review findings

Client.Java-006: close() on both clients only called shutdown(). It now
awaits termination up to the connect timeout and shutdownNow()s on timeout.

Client.Java-007: added MxGatewayLowFindingsTests covering the alarm surface,
async streaming, MxEventStream overflow, and TLS channel construction. A
latent bug surfaced: a missing CA file throws IllegalArgumentException, not
SSLException — the channel-builder catch was broadened accordingly.

Client.Java-008: async thenApply sites now route stray RuntimeExceptions
through MxGatewayErrors.fromGrpc via a normalising validator.

Client.Java-009: extracted ~80 duplicated lines (createChannel, withDeadline,
toCompletable, ...) into a shared MxGatewayChannels; both clients delegate.

Client.Java-010 (re-triaged): the README's metadata:read scope was correct;
the acknowledgeAlarm Javadoc's invoke:alarm-ack was wrong — corrected to the
admin scope.

Client.Java-011: documented the intentional fail-fast event-stream
backpressure in Javadoc and the README.

Client.Java-012: replaced CommonOptions.resolved()'s mutate-and-return-this
with side-effect-free resolvedApiKey()/resolvedTimeout() accessors.

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

clients/java/README.md

@@ -74,10 +74,25 @@ that RPC so a close-time error never replaces the exception a try-with-resources
 body is already propagating. Call `closeRaw()` explicitly when you need to
 observe the close result or handle a close-time failure.
 
+`MxGatewayClient` and `GalaxyRepositoryClient` implement `AutoCloseable`. For a
+client that owns its channel (built with `connect`), the try-with-resources
+`close()` shuts the channel down and waits up to the configured connect timeout
+for termination, forcibly shutting it down on timeout, so in-flight calls and
+Netty event-loop threads are not left running after the block exits. If the
+calling thread is interrupted while waiting, the channel is forcibly shut down
+and the interrupt flag is restored. `closeAndAwaitTermination()` does the same
+but throws `InterruptedException` for callers that want a checked,
+blocking-aware shutdown. `close()` is a no-op for a caller-managed channel.
+
 `MxEventStream` implements `Iterator<MxEvent>` and `AutoCloseable`. Closing it
 cancels the underlying gRPC stream. Canceling or timing out a Java client call
 only stops the client from waiting; it does not abort an in-flight MXAccess COM
-call on the worker STA.
+call on the worker STA. The event stream uses gRPC's default auto-inbound flow
+control with a fixed 16-element buffer and no client-side flow control: this is
+the gateway's documented fail-fast event-backpressure model, so a consumer that
+stalls long enough to fill the buffer triggers an overflow that cancels the
+subscription and surfaces an `MxGatewayException` from the next `next()` call.
+Drain events promptly and be prepared to resubscribe with a resume cursor.
 
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