v1.57.3.0 fix(ship): always-loaded PR-title-version rule + fork-PR title-sync backstop (#1909)

* fix(ship): restore always-loaded PR-title-version invariant to skeleton

The v1.54.0.0 carve moved the 'PR title MUST start with v$NEW_VERSION' rule
out of the always-loaded ship skeleton and entirely into the lazily-loaded
pr-body.md section. The agent only set the version prefix if it happened to
read that section before creating the PR, so PRs landed with bare titles.

Restore a one-line invariant (+ helper reference) to ship/SKILL.md.tmpl right
before the {{SECTION:pr-body}} pointer, mirroring the AUQ always-loaded
precedent. Full procedure stays sectioned. Regenerated all hosts.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* test(ship): guard PR-title-version rule + pull_request_target safety

Two free gate tests so a future carve or workflow refactor can't silently
regress:

- ship-pr-title-version-always-loaded: asserts the invariant lives in the
  always-loaded ship/SKILL.md skeleton (not only sections/), and that the
  skeleton+sections union keeps BOTH the create and the existing-PR update
  title paths. Modeled on test/auq-format-always-loaded.test.ts.
- pr-title-sync-workflow-safety: static tripwire that fails CI if
  pr-title-sync.yml checks out PR-head code or inlines an attacker-controlled
  ${{ github.event.pull_request.* }} field inside a run: block (the two
  pull_request_target footguns actionlint cannot catch).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(ci): pr-title-sync covers fork PRs via hardened pull_request_target

Under plain pull_request the GITHUB_TOKEN is read-only on fork PRs, so the
title-sync backstop could never edit a fork/agent PR title. Switch to
pull_request_target (write token in base context) and make it safe:

- Check out the base repo only (no ref:) — execute trusted infra, never
  fork-head code.
- All attacker-controlled PR fields (title, head repo, head sha) pass via
  env: and are referenced as shell-quoted "$VAR", never inlined into run:.
- Read the PR-head VERSION as data (raw media type) from the head repo at the
  head sha; guard the assignment under set -e.
- Same-repo read failure fails loudly; fork miss warns and skips (the backstop
  stays green without going silently optional).
- Never echo the raw fork title (Actions parses ::workflow-command:: from stdout).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(ship): expand binDir path in pr-body Linked Spec block

ship/sections/pr-body.md.tmpl:98-99 used ${ctx.paths.binDir}, but the
gen-skill-docs generator only resolves {{TOKEN}} syntax in .tmpl files — the
${...} JS-template-literal form is substituted only inside .ts resolver files.
So the token passed through literally into the generated pr-body.md, leaving the
agent with an unexpandable ${ctx.paths.binDir}/gstack-paths command in the
Linked Spec auto-detect block. Use the hardcoded helper path, consistent with
every other path reference in this section.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* refactor(test): fold ship PR-title skeleton guard into carve-guard registry

main shipped a generalized carve-guard system (PR #1907) that is now the single
source of truth for carved-skill skeleton invariants. Register the PR-title rule
there instead of a standalone test: ship's mustStayInSkeleton asserts v$NEW_VERSION
+ the rewrite helper stay always-loaded, and mustMoveToSection asserts both the
create and update PR paths stay carved into pr-body.md (present in the union, out of
the skeleton). Delete the standalone ship-pr-title-version-always-loaded test it
replaces. The CI-workflow safety tripwire stays standalone (not a carve concern).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* chore: bump version and changelog (v1.57.3.0)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

ship/SKILL.md

@@ -1225,6 +1225,8 @@ git push -u origin <branch-name>
 
 ---
 
+**PR/MR title invariant (always applies — do not skip even if you don't open the section below):** Any PR or MR you create OR update in the next step MUST have a title that starts with `v$NEW_VERSION` (the version bumped in Step 12), in the format `v<NEW_VERSION> <type>: <summary>`. Never create or edit a PR/MR title without this prefix. Compute the correct title with the single source of truth helper: `~/.claude/skills/gstack/bin/gstack-pr-title-rewrite.sh "$NEW_VERSION" "<current title>"`. The full create/update procedure (idempotency, redaction scan, self-check) is in the section below.
+
 > **STOP.** Before syncing docs and creating or updating the PR/MR (Steps 18-19), Read `~/.claude/skills/gstack/ship/sections/pr-body.md` and execute it
 > in full. Do not work from memory — that section is the source of truth for this step.