fix: resolve conflicts for PR #416

Merge current prgs/master into feat/issue-399-conflict-fix-leases.
Preserve reviewer PR lease gate (#407) before conflict-fix stale-head
gate (#399); document both as §26B and §26C. Align MCP and validator
tests with mandatory expected_head_sha and stale-head proof fields.

skills/llm-project-workflow/workflows/review-merge-pr.md

@@ -732,7 +732,27 @@ The final report must identify:
 * whether same-PR merge continuation was allowed
 * whether the run stopped as required
 
-## 26B. Conflict-fix lease and stale-head protection (#399)
+## 26B. Per-PR reviewer lease (#407)
+
+Parallel reviewer sessions are allowed only when each session holds a distinct,
+live PR lease.
+
+Before validation or review mutation on a selected PR:
+
+1. Call `gitea_acquire_reviewer_pr_lease` with worktree path, candidate head SHA,
+   and target branch SHA.
+2. Post heartbeats via `gitea_heartbeat_reviewer_pr_lease` before validation,
+   after validation, before review mutation, and before merge.
+3. Do not approve, request changes, or merge unless the in-session lease
+   matches the selected PR.
+
+If PR head or target branch advances during the lease, stop and refresh
+inventory before continuing.
+
+Final reports must include lease session id, acquisition proof, heartbeat
+status, and release/blocked status.
+
+## 26C. Conflict-fix lease and stale-head protection (#399)
 
 Before validating, approving, or merging a PR:
 

skills/llm-project-workflow/workflows/work-issue.md

@@ -297,6 +297,36 @@ Report:
 
 Do not create another branch/PR for the same issue unless the project explicitly allows taking over or updating existing work and exact capability is proven.
 
+### 10A. Duplicate-work gate phases (#400)
+
+Before any file edits, prove duplicate-work clearance with
+`gitea_assess_work_issue_duplicate` or `gitea_lock_issue` (which runs the same
+gate). The gate checks live:
+
+* open PRs linked to the issue (head branch or Closes/Fixes reference),
+* remote branches matching `issue-<number>`,
+* active claim leases from structured heartbeats.
+
+Re-check immediately before:
+
+* `gitea_commit_files` (commit),
+* branch push,
+* `gitea_create_pr` (PR creation).
+
+If a concurrent open PR appears after work begins:
+
+* before commit/push → stop and preserve local work without pushing,
+* after commit but before push → stop without pushing,
+* after push but before PR creation → stop and produce a reconciliation
+  handoff instead of opening a PR.
+
+Final reports must state exactly one duplicate-work outcome:
+
+* `duplicate PR prevented`
+* `duplicate branch prevented`
+* `duplicate commit prevented`
+* `duplicate work not prevented`
+
 ## 11. Claim or lock the issue before implementation
 
 Claim/lock the issue before implementation if the project provides a claim/lock mechanism.
@@ -740,6 +770,12 @@ Use only precise categories:
 * External-state mutations:
 * Read-only diagnostics:
 
+Issue-lock file (`/tmp/gitea_issue_lock.json`) read/write/delete is always an
+external-state mutation. Never claim `External-state mutations: none` after
+seeding, restoring, or removing that file. Manual lock seeding is not a normal
+recovery path (#447); use `gitea_lock_issue` or the #442 adoption recovery path
+instead. Link broader redesign: #438.
+
 `git fetch`, `git remote update`, and any command that updates refs must be listed under `Git ref mutations`, not read-only diagnostics.
 
 If `git reset --hard`, checkout, clean, worktree add/remove, merge simulation, merge abort, or similar commands occurred, report them under `Worktree/index mutations`.