Verification artifacts for issue 12100

Verification artifacts for pingdotgg#12100.

Before: upstream 0b83045, real Codex in an isolated Chromium session and worktree-local T3 server. Two follow-ups queued during sequential shell tools. First dispatched at 17:50:39.989Z, 168 ms after tool.completed, while original turn was running. Both follow-ups became input to that original turn.

After: both remain queued through tool completion; oldest starts a new turn only after original completes; second waits for first follow-up completion. Captured before rebase; repeated successfully on final commit b752e31 after rebasing onto f4ef515 (pingdotgg#12075). final-turns.json contains three completed provider turn IDs and proves non-overlapping start/end timestamps. timeline.json contains selected application events from before and after.

Send now and Ctrl+Shift+Enter steer one queued message while preserving remaining queue/draft. Stop restores remaining queue into existing draft. Focused checks: 338 tests, web typecheck, targeted lint (existing warnings), formatting. Claude Opus 5 review identified a late-checkpoint acknowledgement race. One condition now ignores timestamp-only updates on the previous turn; the focused regression failed before the guard and passes after it. Claude re-review found no issues. Final browser verification was repeated after this guard.

Videos play at 3x speed, with no frames intentionally removed. This is live Codex verification, not a mock provider. Native desktop and other provider runtimes were not exercised. Web and desktop share the changed queue implementation; mobile uses a separate queue.