Behavior: a plugin before_agent_finalize hook that never resolves could previously freeze an agent run forever after a successful compaction retry, with no errors and no recovery from a gateway restart; this was the frozen-runner mechanism behind #84777. before_agent_finalize now has the same 15s default budget as sibling modifying hooks and fails open with the original final answer, converting the freeze into a bounded delay.
Surface: plugin hook runner defaults (src/plugins/hooks.ts), docs/plugins/hooks.md.
Refs #84777.
b2baf799b4
