Parallel detectors with highest-severity short-circuit

[susheem-k]

Summary

Detectors currently run sequentially; all signals are collected, then sorted by severity (TRIP > WARN > OK) and enforced in order. Slow detectors block higher-severity outcomes unnecessarily.

Area: Governor.pre_call / observe / _enforce

Desired behavior

• Run detectors in parallel (thread/async pool as appropriate).
• First highest-severity outcome can cancel/ignore the rest (short-circuit): e.g. any TRIP wins and remaining detector work is aborted when practical.
• Preserve deterministic tie-break (policy priority / name order) when severities equal.
• Keep unit tests deterministic (fake executor or ordered barrier in tests).

Acceptance sketch

• Semantics documented; TRIP from one detector does not wait on slow detectors unnecessarily.
• No flaky tests from scheduling.

Reference: docs/notes/2026-07-23-design-fix-notes.md §16