Replace is held G instead of Ctrl (Ctrl+W/Ctrl+D were hit while flying)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/agent-log.md

@@ -4,6 +4,21 @@ What agents have done, newest first. Add an entry for every piece of work: the d
 note or request it was for, what changed, the files touched, the tests run, and anything left
 open or not verified. Keep each entry short; the git history has the details.
 
+## 2026-10-23: Replace is held G, not Ctrl (Claude Code, with Codex)
+
+Note: "i see the issue was ctrl+w closing the tab… it happens for the bookmark hotkey too. maybe
+change the replace key?" The owner chose holding G.
+
+- `src/ui/input.js`: `GAME.ctrl` became `GAME.replace`, set while G is held. Ctrl no longer
+  does anything on its own, so WASD works while replacing. Ctrl+S, Ctrl+Z, Ctrl+wheel and the
+  leave-page prompt are unchanged.
+- Flag users and text: `previews.js`, `actions.js` ("Hold G to replace it."), `build-menu.js`
+  (Replace · G chip, key hints), `loop.js`, `state.js`, `notebook.js` controls, `docs/DESIGN.md`.
+- `test/play.py`: the replace checks hold G; a new check flies right with D while G is held
+  (121 checks pass). All 11 headless suites pass. `t_smooth.py`'s half-resolution check failed
+  on the slow fallback again (known, flaky under load).
+- Open: nothing.
+
 ## 2026-10-23: Ctrl+W no longer closes the game without asking (Claude Code)
 
 Note: "crash: hoplding crtl and pressing W crashes the whole browser."