[Bug]: [P3] Game input stays live on a dead renderer during in-place recovery

Imported from the engineering backlog (_bmad-output/implementation-artifacts/backlog.md, story context-loss-recovery).
Priority P3 (do-first order) | Severity: low | Status: open | Epic: stability | Type: review-deferral | Recorded: 2026-07-13

What happened?

Game input stays live on a dead renderer during the in-place recovery wait (gds-code-review, Edge Case Hunter). Between a context loss and the restore (up to ~8s of visible time, longer while backgrounded) the canvas is frozen but keyboard shortcuts, the palette, Load/New/Import and the speed buttons all still work, so a player can mutate the sim blind. The crash-screen path mutes game keys via CRASH_SCREEN_ID; the recovery wait has no equivalent guard. Mitigations already shipped: the "Recovering..." toast, gesture-state reset in rebuildEngine, and the tower-swap guard on the success bulletin. If revisited, add a lightweight input gate (like the crash screen's key mute) for the wait window.

Start at the in-place recovery wait and compare its input handling with the crash-screen path using CRASH_SCREEN_ID. Review rebuildEngine and the existing recovery guards; done means keyboard shortcuts, the palette, Load/New/Import, and speed buttons remain inactive until the renderer is restored.