fix: never-Skill prohibition made unambiguous; docsync fixture made diagnostic

The ship-docsync E2E flaked on this sandbox because the driven agent
resolved the STOP pointer's ~ to nonexistent homes (/root, /home) and
acted blind — pass/fail sampled model priors, not the prompt. The
fixture prompt now names the planted sections dir, making local runs
deterministic (CI, with real install paths, was always diagnostic).
With a diagnostic fixture: 2/2 passes, real pr-body read, Agent dispatch
with run_in_background: false, zero Skill-tool substitutions.

Prose: the foreground note now states the dispatch happens ONLY via the
Agent tool (invoking the target as a Skill is wrong even though it
appears in the skills list; inline FALLBACKs apply only after a
dispatched subagent has failed), and the Step 18 imperative carries the
never-the-Skill-tool clause at the decision point.

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

ship/sections/greptile.md

@@ -4,7 +4,7 @@
 
 **Dispatch the fetch + classification as a subagent** using the Agent tool with `subagent_type: "general-purpose"`. The subagent pulls every Greptile comment, runs the escalation detection algorithm, and classifies each comment. Parent receives a structured list and handles user interaction + file edits.
 
-**Foreground required:** pass `run_in_background: false` on the Agent call — subagents run in the BACKGROUND by default since Claude Code v2.1.198. (Merely omitting the flag no longer produces a foreground run; it must be explicitly false.) Dispatch with the Agent tool itself — never substitute the Skill tool or inline execution at initial dispatch to "guarantee" blocking: the explicit flag already makes the Agent call block, and running the work inline forfeits the fresh-context isolation this dispatch exists for.
+**Foreground required:** pass `run_in_background: false` on the Agent call — subagents run in the BACKGROUND by default since Claude Code v2.1.198. (Merely omitting the flag no longer produces a foreground run; it must be explicitly false.) The dispatch happens ONLY via the Agent tool: invoking the target as a Skill, or executing its workflow inline in your own context, is WRONG even though the skill may appear in your available-skills list — inline execution forfeits the fresh-context isolation this dispatch exists for, and the explicit flag already makes the Agent call block. (Where a step defines an inline FALLBACK, it applies only after a dispatched subagent has failed.)
 
 **Subagent prompt:**
 

ship/sections/plan-completion.md

@@ -4,7 +4,7 @@
 
 **Dispatch this step as a subagent** using the Agent tool with `subagent_type: "general-purpose"`. The subagent reads the plan file and every referenced code file in its own fresh context. Parent gets only the conclusion.
 
-**Foreground required:** pass `run_in_background: false` on the Agent call — subagents run in the BACKGROUND by default since Claude Code v2.1.198. (Merely omitting the flag no longer produces a foreground run; it must be explicitly false.) Dispatch with the Agent tool itself — never substitute the Skill tool or inline execution at initial dispatch to "guarantee" blocking: the explicit flag already makes the Agent call block, and running the work inline forfeits the fresh-context isolation this dispatch exists for. The Gate Logic below consumes this audit's LAST-line JSON before /ship can proceed.
+**Foreground required:** pass `run_in_background: false` on the Agent call — subagents run in the BACKGROUND by default since Claude Code v2.1.198. (Merely omitting the flag no longer produces a foreground run; it must be explicitly false.) The dispatch happens ONLY via the Agent tool: invoking the target as a Skill, or executing its workflow inline in your own context, is WRONG even though the skill may appear in your available-skills list — inline execution forfeits the fresh-context isolation this dispatch exists for, and the explicit flag already makes the Agent call block. (Where a step defines an inline FALLBACK, it applies only after a dispatched subagent has failed.) The Gate Logic below consumes this audit's LAST-line JSON before /ship can proceed.
 
 **Subagent prompt:** Pass these instructions to the subagent:
 

ship/sections/pr-body.md

@@ -2,9 +2,9 @@
 <!-- Regenerate: bun run gen:skill-docs -->
 ## Step 18: Documentation sync (via subagent, before PR creation)
 
-**Dispatch /document-release as a subagent** using the Agent tool with `subagent_type: "general-purpose"`. The subagent gets a fresh context window — zero rot from the preceding 17 steps. It also runs the **full** `/document-release` workflow (with CHANGELOG clobber protection, doc exclusions, risky-change gates, named staging, race-safe PR body editing) rather than a weaker reimplementation. The dispatch prompt marks the subagent session as spawned (`GSTACK_SESSION_KIND=spawned`) so document-release's interactive gates auto-choose their recommended options instead of prose-stopping — a prose-STOP inside the subagent breaks the parent's LAST-line JSON parse and drops the Documentation section (#2733).
+**Dispatch /document-release as a subagent** using the Agent tool — never the Skill tool, even though document-release appears in your skills list — with `subagent_type: "general-purpose"`. The subagent gets a fresh context window — zero rot from the preceding 17 steps. It also runs the **full** `/document-release` workflow (with CHANGELOG clobber protection, doc exclusions, risky-change gates, named staging, race-safe PR body editing) rather than a weaker reimplementation. The dispatch prompt marks the subagent session as spawned (`GSTACK_SESSION_KIND=spawned`) so document-release's interactive gates auto-choose their recommended options instead of prose-stopping — a prose-STOP inside the subagent breaks the parent's LAST-line JSON parse and drops the Documentation section (#2733).
 
-**Foreground required:** pass `run_in_background: false` on the Agent call — subagents run in the BACKGROUND by default since Claude Code v2.1.198. (Merely omitting the flag no longer produces a foreground run; it must be explicitly false.) Dispatch with the Agent tool itself — never substitute the Skill tool or inline execution at initial dispatch to "guarantee" blocking: the explicit flag already makes the Agent call block, and running the work inline forfeits the fresh-context isolation this dispatch exists for. Step 19 consumes this subagent's LAST-line JSON, so the dispatch must block — a backgrounded dispatch strands the entire ship run (#497, #2440: third recurrence of this class). Record `git rev-parse HEAD` immediately before dispatching; the recovery branch below reconciles against it.
+**Foreground required:** pass `run_in_background: false` on the Agent call — subagents run in the BACKGROUND by default since Claude Code v2.1.198. (Merely omitting the flag no longer produces a foreground run; it must be explicitly false.) The dispatch happens ONLY via the Agent tool: invoking the target as a Skill, or executing its workflow inline in your own context, is WRONG even though the skill may appear in your available-skills list — inline execution forfeits the fresh-context isolation this dispatch exists for, and the explicit flag already makes the Agent call block. (Where a step defines an inline FALLBACK, it applies only after a dispatched subagent has failed.) Step 19 consumes this subagent's LAST-line JSON, so the dispatch must block — a backgrounded dispatch strands the entire ship run (#497, #2440: third recurrence of this class). Record `git rev-parse HEAD` immediately before dispatching; the recovery branch below reconciles against it.
 
 **Sequencing:** This step runs AFTER Step 17 (Push) and BEFORE Step 19 (Create PR). The PR is created once from final HEAD with the `## Documentation` section baked into the initial body. No create-then-re-edit dance.
 

ship/sections/pr-body.md.tmpl

@@ -1,6 +1,6 @@
 ## Step 18: Documentation sync (via subagent, before PR creation)
 
-**Dispatch /document-release as a subagent** using the Agent tool with `subagent_type: "general-purpose"`. The subagent gets a fresh context window — zero rot from the preceding 17 steps. It also runs the **full** `/document-release` workflow (with CHANGELOG clobber protection, doc exclusions, risky-change gates, named staging, race-safe PR body editing) rather than a weaker reimplementation. The dispatch prompt marks the subagent session as spawned (`GSTACK_SESSION_KIND=spawned`) so document-release's interactive gates auto-choose their recommended options instead of prose-stopping — a prose-STOP inside the subagent breaks the parent's LAST-line JSON parse and drops the Documentation section (#2733).
+**Dispatch /document-release as a subagent** using the Agent tool — never the Skill tool, even though document-release appears in your skills list — with `subagent_type: "general-purpose"`. The subagent gets a fresh context window — zero rot from the preceding 17 steps. It also runs the **full** `/document-release` workflow (with CHANGELOG clobber protection, doc exclusions, risky-change gates, named staging, race-safe PR body editing) rather than a weaker reimplementation. The dispatch prompt marks the subagent session as spawned (`GSTACK_SESSION_KIND=spawned`) so document-release's interactive gates auto-choose their recommended options instead of prose-stopping — a prose-STOP inside the subagent breaks the parent's LAST-line JSON parse and drops the Documentation section (#2733).
 
 {{FOREGROUND_DISPATCH_NOTE}} Step 19 consumes this subagent's LAST-line JSON, so the dispatch must block — a backgrounded dispatch strands the entire ship run (#497, #2440: third recurrence of this class). Record `git rev-parse HEAD` immediately before dispatching; the recovery branch below reconciles against it.
 

ship/sections/test-coverage.md

@@ -4,7 +4,7 @@
 
 **Dispatch this step as a subagent** using the Agent tool with `subagent_type: "general-purpose"`. The subagent runs the coverage audit in a fresh context window — the parent only sees the conclusion, not intermediate file reads. This is context-rot defense.
 
-**Foreground required:** pass `run_in_background: false` on the Agent call — subagents run in the BACKGROUND by default since Claude Code v2.1.198. (Merely omitting the flag no longer produces a foreground run; it must be explicitly false.) Dispatch with the Agent tool itself — never substitute the Skill tool or inline execution at initial dispatch to "guarantee" blocking: the explicit flag already makes the Agent call block, and running the work inline forfeits the fresh-context isolation this dispatch exists for. The parent needs this audit's LAST-line JSON before continuing.
+**Foreground required:** pass `run_in_background: false` on the Agent call — subagents run in the BACKGROUND by default since Claude Code v2.1.198. (Merely omitting the flag no longer produces a foreground run; it must be explicitly false.) The dispatch happens ONLY via the Agent tool: invoking the target as a Skill, or executing its workflow inline in your own context, is WRONG even though the skill may appear in your available-skills list — inline execution forfeits the fresh-context isolation this dispatch exists for, and the explicit flag already makes the Agent call block. (Where a step defines an inline FALLBACK, it applies only after a dispatched subagent has failed.) The parent needs this audit's LAST-line JSON before continuing.
 
 **Subagent prompt:** Pass the following instructions to the subagent, with `<base>` substituted with the base branch: