quest: plan keeping .worktrees/ out of git status

quest/m0/user-dev-shell/README.md

@@ -73,4 +73,5 @@ moq-dev/moq's `.codex/hooks/direnv.sh`.
 
 ## Required
 
+- [.worktrees/ stays out of git status](/quest/m0/user-dev-shell/worktrees-exclude.md) - `quest worktree` adds `/.worktrees/` to the clone's local exclude unless something ignores it
 - [Repositories drop dev-shell config](/quest/m0/user-dev-shell/repo-config.md) - quest, moq, moq.pro, rind, and rust2 drop their dev-shell hooks and `nix develop` instructions

quest/m0/user-dev-shell/worktrees-exclude.md

@@ -0,0 +1,39 @@
+# [S] .worktrees/ stays out of git status
+
+## Goal
+
+When `quest worktree` creates a checkout under a repository's `.worktrees/`,
+it adds `/.worktrees/` to that repository's `$GIT_COMMON_DIR/info/exclude`
+unless something already ignores the directory, so the main checkout's
+`git status` never lists `.worktrees/`. The exclude is local to the clone:
+no repository change, and every checkout of it shares the file.
+
+## Plan
+
+Decided 2026-11-04 (user, /quest-complete follow-up of
+[moq-dev/quest#466](https://github.com/moq-dev/quest/pull/466)). With
+Quest's worktree hooks an opt-in in each user's own Claude settings, they
+run in every repository the user opens, and a repository that doesn't ignore
+`.worktrees/` shows `?? .worktrees/` in its main checkout (reproduced with
+`git worktree add .worktrees/a` in a fresh repository; nothing in
+`src/cli/worktree.ts` writes an exclude).
+
+- What should the quest's goal be?
+  - ✅ A local exclude written by `quest worktree`
+  - Rejected: telling users to add `.worktrees/` to their global gitignore;
+    leaving it
+- Which milestone and epic?
+  - ✅ m0, in this epic beside the opt-in that exposed it
+  - Rejected: m1; m2
+
+Implementation guidance:
+
+- Check with `git check-ignore`, as `ignored()` in `src/cli/worktree.ts`
+  does, whether `.worktrees/` is already ignored, by the repository, a
+  global `core.excludesFile`, or an earlier exclude, before appending.
+  Query it with the trailing slash: until the directory exists,
+  `git check-ignore .worktrees` misses a directory-only rule such as
+  `/.worktrees/`.
+- Test with a repository that has no ignore rule, one whose `.gitignore`
+  already lists `/.worktrees/`, and a second checkout, which must not
+  append the line again.