fix(agent): bound authorization gate lock acquire and cap excluded_seconds (#79719)

[RelaxJonh]

Summary

Two coupled problems in _ConcurrentToolAuthorizationGate (agent/tool_executor.py):

1. self._serialization_lock is an unbounded blocking acquire. If the worker holding it wedges (hung pre_tool_block plugin, dead approval client), every other worker needing authorization blocks behind it forever.

2. excluded_seconds() grows 1:1 with wall clock. The batch-deadline loop adds it to the deadline on every poll (tool_executor.py:1168,1190), so remaining is constant and the deadline never fires — the turn hangs indefinitely.

Fix

• Add a 120s timeout to _serialization_lock.acquire(). On timeout, log a warning and proceed in degraded mode (run the callback without serialization) rather than hanging forever.
• Cap excluded_seconds() at _MAX_EXCLUDED_SECONDS (120s) so the batch deadline can eventually fire.

Tests

• test_excluded_seconds_capped — verifies the cap is enforced
• test_lock_timeout_proceeds — verifies a second caller proceeds when the lock is held too long
• test_normal_operation_unaffected — verifies normal non-wedged calls work as before

Closes #79719

[kshitijk4poor]

Thanks for the fix — bounding the serialization lock and capping the exclusion were the right two levers for #79719.

We ended up fixing it via #80297, which restructures the exclusion instead of capping it: a flat cap on total excluded_seconds (as here) would also truncate legitimate approval waits — two real 90s approvals in one batch would exhaust a 120s budget, and a single legit approval can run to approvals.timeout (300s default), past the cap. #80297 measures the exclusion at the source of the human wait (tools/approval.py marks the CLI prompt and gateway approval poll loop as explicit windows), so a wedged plugin contributes zero exclusion while genuine approvals are excluded in full, and the lock bound is derived from approvals.timeout rather than fixed. You're credited in the PR body.

Closing in favor of #80297. Thanks again!