fix(recorder): keep late progress updates from rewriting the state being sealed

[abrichr]

Problem

tests/test_control.py::test_concurrent_repeated_stop_is_idempotent fails intermittently on test-macos:

• 2026-10-14 run 38601787804: both stop callers get CaptureControlError('Capture control failed: capture_seal_failed')
• 2026-08-27, on older code: the same test fails with recording_or_finalization_failed

Root cause

This is a real race in Recorder, not just a slow test. A timeout bump would not fix it.

1. After record() returns, _run_record writes the final capture-state.json (_stage_completed_control_state). It then calls seal_capture, which inventories every file in the capture directory, including that file, and verifies the inventory.
2. _transition_control only refused updates once the in-memory phase was terminal. That phase becomes complete only after the seal. During the seal, any non-terminal transition still rewrote capture-state.json:
   • the status-drain thread handling a late record.stopping → finalizing, which happens when that thread is scheduled late on a loaded runner, or
   • a stop caller's finalization_timeout transition.
3. If the rewrite lands during the seal, an inventoried artifact changes (or its atomic-write temp file appears), and the stop returns capture_seal_failed. If it lands just before the seal, the capture seals a stale finalizing state.

Reproduced deterministically: delivering the finalizing update right after build_artifact_manifest returns gives exactly capture_seal_failed.

Fix

Once the final state is staged, _transition_control ignores non-terminal transitions. That file now belongs to the seal. A terminal outcome, such as a seal failure marking the capture failed, can still replace it. A stop caller that times out still gets its finalization_timeout response; the timeout just no longer rewrites a sealed artifact.

Test

Added test_late_progress_update_cannot_rewrite_the_state_being_sealed. It runs an in-process recorder and delivers late finalizing and finalization_timeout updates in the middle of the seal.

• Without the fix it fails with capture_seal_failed.
• With it, the stop completes, verify_capture_artifacts passes, and the sealed state is complete.

Locally on macOS: tests/test_control.py passed 5 runs in a row, and the full non-slow suite passed (871 passed).