fix: adversarial review fixes — failure shape, CHANGELOG guard, vet coherence

Claude adversarial subagent findings (11), all verified before applying:
- The dispatch JSON contract gains an explicit FAILURE shape
  ({"error":...}) and a parent branch for it — a doc-sync that could not
  run (spawned marking failed, broken preamble) previously had only the
  no-updates shape to emit, which the parent printed as 'Documentation is
  current': a silent false-clean of exactly the VAS-449 class.
- Scope guard now covers CHANGELOG: skip Step 5 voice polish and resolve
  CHANGELOG-touching gates to leave-as-is (the parent authored the
  release entry; the prompt's older auto-choose clause conflicted with
  the contract's never-rewrite invariant).
- Recovery vet is sequence-coherent: pushing a commit pushes its
  ancestors, so ANY non-doc commit (VERSION, package.json, CHANGELOG.md)
  blocks the whole sequence — no more push-the-vetted-child-of-an-
  unvetted-parent hole.
- Steps 7/8/10 failure branches stop a still-running backgrounded task
  before falling back, so a late result never races the inline audit.
- 'Documentation synced' print gated on pushed:true (item 6 owns the
  local-only outcome); doc-review skip note's backward step pointer
  fixed; foreground note scoped 'at initial dispatch' so the sanctioned
  inline FALLBACKS in Steps 7/8 read as sanctioned; constants docstring
  no longer overclaims single-sourcing (names the 3 inline templates).
- Runtime-hook TODO raised P2 → P1: the spawned trust chain is
  agent-self-asserted; prose cannot close it, the hook can.

Both docsync gate E2Es re-verified green on the amended prompt, including
the strict run_in_background === false dispatch assert.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

TODOS.md

@@ -2381,9 +2381,11 @@ Linux cookie import shipped in v0.11.11.0 (Wave 3). Supports Chrome, Chromium, B
 **Context:** Third recurrence of the class (#497 → #2440 → /ship Step 18 stranding). The hook must scope to gstack skill sessions (never break legitimate background Agent use elsewhere), is Claude-host only (other hosts get nothing from it), and mirrors the existing question-preference PreToolUse hook wiring in `bin/gstack-settings-hook*`. Filed from the v1.79.0.0 CEO plan review (approach C, deliberately split out for bake time).
 
 **Effort:** M (human) / S (CC)
-**Priority:** P2
+**Priority:** P1
 **Depends on:** None
 
+*Priority raised P2 → P1 by the v1.79.0.0 adversarial review: the spawned trust chain is agent-self-asserted (the echo exists because the agent typed the env prefix a prompt told it to), so instruction text read before the preamble can convert an interactive run to full-auto. Prose cannot close this; the hook can.*
+
 ### Structural ship-mode for document-release
 
 **What:** A capability-narrowed dispatch mode for /document-release (cannot bump VERSION, run review passes, or push) instead of narrowing the full workflow through prose in /ship's dispatch prompt; the parent /ship owns all git operations.