Merge pull request 'feat: add root checkout guard for contaminated control checkout (Closes #475)' (#488) from feat/issue-475-root-checkout-guard into master

docs/llm-workflow-runbooks.md

@@ -377,6 +377,37 @@ explicit control-checkout repair.
 
 Portable wording: [`skills/llm-project-workflow/SKILL.md`](../skills/llm-project-workflow/SKILL.md).
 
+### Root checkout guard (#475)
+
+The MCP server enforces a fail-closed **root checkout guard** before author,
+reviewer, and merger mutations when the active workspace is not an isolated
+`branches/...` worktree (reconciler close paths remain exempt per #468).
+
+The guard blocks when the **control checkout** (repository root) is:
+
+- on a non-stable branch (`master` / `main` / `dev` expected),
+- detached HEAD,
+- dirty (tracked edits),
+- or its `HEAD` does not match `prgs/master` when that ref is available.
+
+**Remediation (never auto-reset or stash):**
+
+> Root checkout is not on master. Preserve state, switch root back to master,
+> and use `scripts/worktree-review` or the sanctioned issue worktree flow.
+
+**Recovery after root hijack:**
+
+1. Preserve any in-progress edits (copy paths, note branch name, or commit on a
+   rescue branch from a `branches/...` worktree).
+2. From the repository root: `git checkout master` (or `main` / `dev` per repo
+   policy) and `git fetch prgs && git merge --ff-only prgs/master` when safe.
+3. Confirm `git status` is clean and `git branch --show-current` is `master`.
+4. Resume work only inside `branches/issue-<n>-<slug>` via `gitea_lock_issue` /
+   `git worktree add`.
+
+`branches/...` directories are disposable role worktrees; the root checkout is
+the stable orchestration surface only.
+
 ## Shell Spawn Hard-Stop Rule
 
 Symptom: a shell tool call returns `exit_code: -1` with empty stdout/stderr.