GovernorContainer: process-global governors keyed by run_id with TTL cleanup

[susheem-k]

Summary

Today: new Governor per handler call. Shared spend already lives in SQLite; request-local Governors avoid shared in-memory windows but push construction onto the user and duplicate wiring.

Area: Governor lifecycle, concurrency, cleanup

Desired behavior

• Top-level GovernorContainer (name TBD) is process-global / singleton-friendly.
• Internally holds per-run_id Governor (or run state) instances.
• pre_call / observe route by run_id from ambient attribution.
• Periodic cleanup of completed / halted / TTL-expired runs’ local state.
• Cloning from prototype (§10) when a run is first seen.

Acceptance sketch

• Agent code does not build_governor per request; it talks to the container (or ambient scope does).
• Concurrent runs in one process do not share step windows.

Reference: docs/notes/2026-07-23-design-fix-notes.md §11