docs: add Work Selection Rule for LLM operating rules

Require lease verification (open PRs, branches, worktrees, leases,
merged completion) before any issue or PR work. Surface the rule in
the portable skill, Gitea runbooks, operator guide, and start-issue
template; add doc-contract tests.

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

docs/llm-workflow-runbooks.md

@@ -229,6 +229,34 @@ Legacy environment-only setups keep working unchanged until migrated.
 Each runbook names the **profile role** it runs under, the steps, and a safe
 prompt. Confirm the active profile first (`gitea_get_profile` / `gitea_whoami`).
 
+## Work Selection Rule for LLMs
+
+Before starting any issue or PR work, acquire or verify a work lease. Do not
+begin coding, reviewing, fixing, branching, committing, pushing, commenting,
+or creating a PR until you prove the target is not already being worked.
+
+Required checks:
+
+1. List open PRs.
+2. Search for PRs linked to the target issue.
+3. Search local and remote branches for the issue number.
+4. Search registered worktrees for the issue branch.
+5. Check dirty worktrees.
+6. Check active leases or recent handoffs.
+7. Check whether the issue was already completed by a merged PR.
+
+If another active LLM/session owns the lease, stop. Allowed responses:
+continue as the lease owner; review the existing PR if reviewer capability
+allows; produce a handoff; request takeover after lease expiry; stop with
+"work already claimed."
+
+Never create a parallel branch or PR for the same issue unless the old branch
+is proven abandoned and the takeover is recorded.
+
+Gitea-Tools lease gates: `gitea_lock_issue` (fail-closed before author
+mutations), `status:in-progress`, and claim comments. Full portable wording:
+[`skills/llm-project-workflow/SKILL.md`](../skills/llm-project-workflow/SKILL.md).
+
 ## Branch worktree isolation
 
 All LLM implementation and review work happens in an isolated branch worktree

docs/wiki/Workflow.md

@@ -14,6 +14,9 @@
 
 ## Step 2: Implement issues (author profile)
 
+0. Work Selection Rule — verify a work lease before any mutations (open PRs,
+   issue-linked PRs, branches, worktrees, dirty worktrees, active leases/
+   handoffs, merged-PR completion). Stop if another session owns the lease.
 1. `gitea_resolve_task_capability` for the author task.
 2. `gitea_lock_issue` before implementation mutations.
 3. Claim with `gitea_mark_issue` / `status:in-progress` label.