Gap closure: feedback loops, traceability, and new /content-audit skill

- NEW /content-audit skill: GDD-specified content vs implemented content gap
  report with COMPLETE/IN PROGRESS/EARLY/NOT STARTED per system
- balance-check: Fix & Verify Cycle phase (fix → re-verify → propagate-design-change)
- perf-profile: Scope & Timeline Decision phase for M/L effort optimizations
- playtest-report: Action Routing phase categorizes findings → design/balance/bugs/polish
- review-all-gdds: Phase 4 Cross-System Scenario Walkthrough (multi-system sequences)
- story-done: Test-Criterion Traceability (each AC mapped to a test, BLOCKING if >50% untested)
- code-review: ADR Compliance Check (ARCHITECTURAL VIOLATION / ADR DRIFT / MINOR DEVIATION)
- setup-engine: upgrade subcommand (pre-upgrade API scan, migration plan, VERSION.md update)
- story-readiness: Asset References Check (verifies referenced asset paths exist)
- validate-assets.sh: invalid JSON now exits 1 (blocking); naming issues exit 0 (warning)
- workflow-catalog.yaml + sprint-plan: /scope-check wired into production phase

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/skills/setup-engine/SKILL.md

@@ -1,7 +1,7 @@
 ---
 name: setup-engine
 description: "Configure the project's game engine and version. Pins the engine in CLAUDE.md, detects knowledge gaps, and populates engine reference docs via WebSearch when the version is beyond the LLM's training data."
-argument-hint: "[engine version] or no args for guided selection"
+argument-hint: "[engine version] | refresh | upgrade [old-version] [new-version] | no args for guided selection"
 user-invocable: true
 allowed-tools: Read, Glob, Grep, Write, Edit, WebSearch, WebFetch, Task
 ---
@@ -10,11 +10,13 @@ When this skill is invoked:
 
 ## 1. Parse Arguments
 
-Three modes:
+Four modes:
 
 - **Full spec**: `/setup-engine godot 4.6` — engine and version provided
 - **Engine only**: `/setup-engine unity` — engine provided, version will be looked up
 - **No args**: `/setup-engine` — fully guided mode (engine recommendation + version)
+- **Refresh**: `/setup-engine refresh` — update reference docs (see Section 10)
+- **Upgrade**: `/setup-engine upgrade [old-version] [new-version]` — migrate to a new engine version (see Section 11)
 
 ---
 
@@ -275,7 +277,112 @@ If invoked as `/setup-engine refresh`:
 
 ---
 
-## 11. Output Summary
+## 11. Upgrade Subcommand
+
+If invoked as `/setup-engine upgrade [old-version] [new-version]`:
+
+### Step 1 — Read Current Version State
+
+Read `docs/engine-reference/<engine>/VERSION.md` to confirm the current pinned
+version, risk level, and any migration note URLs already recorded. If
+`old-version` was not provided as an argument, use the pinned version from this
+file.
+
+### Step 2 — Fetch Migration Guide
+
+Use WebSearch and WebFetch to locate the official migration guide between
+`old-version` and `new-version`:
+
+- Search: `"[engine] [old-version] to [new-version] migration guide"`
+- Search: `"[engine] [new-version] breaking changes changelog"`
+- Fetch the migration guide URL from VERSION.md if one is already recorded,
+  or use the URL found via search.
+
+Extract: renamed APIs, removed APIs, changed defaults, behavior changes, and
+any "must migrate" items.
+
+### Step 3 — Pre-Upgrade Audit
+
+Scan `src/` for code that uses APIs known to be deprecated or changed in the
+target version:
+
+- Use Grep to search for deprecated API names extracted from the migration
+  guide (e.g., old function names, removed node types, changed property names)
+- List each file that matches, with the specific API reference found
+
+Present the audit results as a table:
+
+```
+Pre-Upgrade Audit: [engine] [old-version] → [new-version]
+==========================================================
+
+Files requiring changes:
+  File                              | Deprecated API Found       | Effort
+  --------------------------------- | -------------------------- | ------
+  src/gameplay/player_movement.gd   | old_api_name               | Low
+  src/ui/hud.gd                     | removed_node_type          | Medium
+
+Breaking changes to watch for:
+  - [change description from migration guide]
+  - [change description from migration guide]
+
+Recommended migration order (dependency-sorted):
+  1. [system/layer with fewest dependencies first]
+  2. [next system]
+  ...
+```
+
+If no deprecated APIs are found in `src/`, report: "No deprecated API usage
+found in src/ — upgrade may be low-risk."
+
+### Step 4 — Confirm Before Updating
+
+Ask the user before making any changes:
+
+> "Pre-upgrade audit complete. Found [N] files using deprecated APIs.
+> Proceed with upgrading VERSION.md to [new-version]?
+> (This will update the pinned version and add migration notes — it does NOT
+> change any source files. Source migration is done manually or via stories.)"
+
+Wait for explicit confirmation before continuing.
+
+### Step 5 — Update VERSION.md
+
+After confirmation:
+
+1. Update `docs/engine-reference/<engine>/VERSION.md`:
+   - `Engine Version` → `[new-version]`
+   - `Project Pinned` → today's date
+   - `Last Docs Verified` → today's date
+   - Re-evaluate and update the `Risk Level` and `Post-Cutoff Version Timeline`
+     table if the new version falls beyond the LLM knowledge cutoff
+   - Add a `## Migration Notes — [old-version] → [new-version]` section
+     containing: migration guide URL, key breaking changes, deprecated APIs
+     found in this project, and recommended migration order from the audit
+
+2. If `breaking-changes.md` or `deprecated-apis.md` exist in the engine
+   reference directory, append the new version's changes to those files.
+
+### Step 6 — Post-Upgrade Reminder
+
+After updating VERSION.md, output:
+
+```
+VERSION.md updated: [engine] [old-version] → [new-version]
+
+Next steps:
+1. Migrate deprecated API usages in the [N] files listed above
+2. Run /setup-engine refresh after upgrading the actual engine binary to
+   verify no new deprecations were missed
+3. Run /architecture-review — the engine upgrade may invalidate ADRs that
+   reference specific APIs or engine capabilities
+4. If any ADRs are invalidated, run /propagate-design-change to update
+   downstream stories
+```
+
+---
+
+## 12. Output Summary
 
 After setup is complete, output: