The mid-turn queue drain request sent after every tool batch awaited the
client's response with no deadline. A client that silently drops unknown
methods instead of rejecting with JSON-RPC -32601 never answers, wedging
every tool-calling prompt turn. Race the drain against a 2s timeout and
latch the feature off after three consecutive timeouts.
Also make the integration-test ACP client spec-conforming: reply -32601
to unknown agent->client requests instead of ignoring them.