The base adapter's active-session guard queues all messages when an agent
is running. This creates a deadlock for /approve and /deny: the agent
thread is blocked on threading.Event.wait() in tools/approval.py waiting
for resolve_gateway_approval(), but the /approve command is queued waiting
for the agent to finish.
Dispatch /approve and /deny directly to the message handler (which routes
to gateway/run.py's _handle_approve_command) without going through
_process_message_background — avoids spawning a competing background task
that would mess with session lifecycle/guards.
Fixes#4898
Co-authored-by: mechovation (original diagnosis in PR #4904)
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