docs: add Global LLM Worktree Rule to operating rules (#272)

Require mutations only from branches/ worktrees after proving project
root, cwd, branch, stable main-checkout branch, and session worktree
path. Surface in portable skill, runbooks, wiki, operator guide, and
start-issue template.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

skills/llm-project-workflow/SKILL.md

@@ -89,10 +89,37 @@ mutations; `status:in-progress` and claim comments are supporting lease signals.
 Use `review_proofs.classify_issue_for_selection` when reporting fresh issue
 selection (#188).
 
+## Global LLM Worktree Rule
+
+The main project checkout is a stable control checkout. It must stay on the
+configured stable branch: `master`, `main`, or `dev`.
+
+All LLM task work must happen inside the project's `branches/` directory.
+
+Before any mutation, prove:
+
+1. current project root
+2. current working directory
+3. current branch
+4. stable branch for the main checkout
+5. session-owned worktree path under `branches/`
+
+If `cwd` is not inside `branches/`, stop. Do not edit, create, delete, format,
+test-write, commit, merge, rebase, checkout task branches, resolve conflicts,
+or run cleanup.
+
+There are no exceptions for small fixes, docs, tests, cleanup, PR review fixes,
+conflict resolution, or emergencies.
+
+The main checkout may only be used for read-only inspection, fetching,
+stable-branch update after merged PRs, creating `branches/` worktrees, or
+explicit control-checkout repair.
+
 ## B. Isolated worktree rule
 
-**Never implement or review in the main checkout.** The main checkout is for
-orchestration and status only (issue creation, `git status`, creating worktrees).
+**Never implement or review in the main checkout** (Global LLM Worktree Rule).
+The main checkout is for orchestration and status only (issue creation,
+`git status`, creating worktrees) and must remain on the stable branch.
 
 - Each issue gets its own branch worktree under an ignored `branches/` directory.
 - Review work uses a **separate** review worktree, never the author's folder.
@@ -180,7 +207,10 @@ Worktree folder = branch with `/` replaced by `-`
 
 0. Acquire or verify a work lease (Work Selection Rule) — complete all seven
    checks before any claim, branch, or PR work.
-1. Verify the orchestration checkout (right repo, clean tree).
+0b. Global LLM Worktree Rule — prove project root, `cwd`, branch, main-checkout
+    stable branch, and session-owned `branches/` worktree path. If `cwd` is not
+    under `branches/`, stop before any mutation (no exceptions).
+1. Verify the orchestration checkout (right repo, clean tree, on stable branch).
 2. Fetch/prune: `git fetch <remote> --prune`.
 3. Confirm local `master` equals remote `master` (`git rev-list --left-right --count <remote>/master...master` → `0	0`).
 4. Create/claim the issue (§A).

skills/llm-project-workflow/templates/start-issue.md

@@ -22,6 +22,12 @@ Steps:
    as lease owner, review the existing PR, hand off, request takeover after
    expiry, or report "work already claimed"). Never open a parallel branch/PR
    unless the old branch is proven abandoned and takeover is recorded.
+0b. Global LLM Worktree Rule — before any mutation, prove and state: project
+   root; cwd; current branch; stable branch for the main checkout (master/main/dev);
+   session-owned worktree path under branches/. If cwd is not inside branches/,
+   STOP (no exceptions — not for docs, tests, small fixes, review fixes, conflicts,
+   or cleanup). Main checkout is control-only: read-only inspect, fetch, create
+   worktrees, stable-branch update after merge, explicit repair.
 1. Identity Checklist: Before claiming work, verify and state:
    - Required identity/profile for this task: author (allowed to push branches / create PRs)
    - Current authenticated identity (from whoami): <username>