Improvements for connection desynchronization and hardening of error handling with connections (#1998)

Close desynchronized connections and harden response handling

Detect responseTo mismatches before processing response bodies so session
state is not advanced from an unrelated reply, and close the connection to
prevent desynchronized streams from returning to the pool.

Ensure read and post-read failures close connections only when appropriate,
release buffers before closing, preserve fatal Error propagation, and keep
command monitoring to one started event and one terminal event across sync
and async paths.

Add unit coverage for responseTo mismatch handling, reusable exception paths,
buffer release ordering, and sync/async error handling. Document related
JUnit test conventions.

JAVA-6210

Author: rozza

.agents/references/testing-guide.md

@@ -29,6 +29,15 @@ description: Testing frameworks, conventions, and commands for the MongoDB Java
 - Descriptive method names: `shouldReturnEmptyListWhenNoDocumentsMatch()` not `test1()`
 - Use `@DisplayName` for human-readable names
 - Clean up test data in `@AfterEach` / `cleanup()` to prevent pollution
+- Import types at the top of the file — do not use inline fully-qualified names
+  (`com.mongodb.connection.AsyncCompletionHandler`, `java.util.List`) in signatures or bodies
+- Use `AtomicInteger` / `AtomicBoolean` for mutable state captured by lambdas or anonymous
+  classes — not single-element array wrappers (`int[]`, `boolean[]`)
+- Assert the most specific exception type the code guarantees
+  (`assertInstanceOf(MongoCommandException.class, e)`, not `Exception.class`)
+- When testing that a side effect happens on condition X (e.g. connection closed on stream
+  desync), also test that it does NOT happen on the neighbouring condition Y (e.g. connection
+  stays open on a command error) — one-sided tests let behavioral regressions through
 
 ## Running Tests