Pipeline integrity + brownfield adoption system

Pipeline integrity (4 fixes for snapshot-vs-live-reference problem):
- NEW docs/architecture/tr-registry.yaml: persistent stable TR-IDs per GDD
  requirement; /architecture-review bootstraps and appends, never renumbers
- /create-control-manifest: added Manifest Version stamp to header
- /create-epics-stories: stories embed TR-ID reference (not quoted text),
  Manifest Version from manifest, ADR status gate (Proposed → Blocked)
- /story-done: TR-ID registry lookup at review time, manifest staleness check
- /story-readiness: ADR Accepted check, TR-ID validity, manifest version check
- /review-all-gdds + /architecture-review: fixed parenthetical status values
  ("Needs Revision" only, no parentheticals that break exact-match reads)

Workflow infrastructure:
- NEW /help skill: context-aware "what's next" using workflow-catalog.yaml
- NEW .claude/docs/workflow-catalog.yaml: YAML-driven phase/step sequence
- /sprint-plan + /sprint-status: sprint-status.yaml machine-written tracking

Brownfield adoption system (migrate, not replace):
- NEW /adopt skill: format compliance audit (not existence check); classifies
  gaps BLOCKING/HIGH/MEDIUM/LOW; produces docs/adoption-plan-[date].md with
  numbered migration plan; never regenerates existing artifacts
- /design-system retrofit [path]: fills only missing GDD sections, preserves
  all existing content
- /architecture-decision retrofit [path]: adds missing ADR sections (Status,
  ADR Dependencies, Engine Compatibility) without touching existing content
- /start option D: split into D1 (early-stage) and D2 (has GDDs/ADRs → adopt)

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

.claude/skills/design-system/SKILL.md

@@ -10,13 +10,45 @@ When this skill is invoked:
 
 ## 1. Parse Arguments & Validate
 
-A system name argument is **required**. If missing, fail with:
+A system name or retrofit path is **required**. If missing, fail with:
 > "Usage: `/design-system <system-name>` — e.g., `/design-system combat-system`
+> Or to fill gaps in an existing GDD: `/design-system retrofit design/gdd/combat-system.md`
 > Run `/map-systems` first to create the systems index, then use this skill
 > to write individual system GDDs."
 
-Normalize the system name to kebab-case for the filename (e.g., "combat system"
-becomes `combat-system`).
+**Detect retrofit mode:**
+If the argument starts with `retrofit` or the argument is a file path to an
+existing `.md` file in `design/gdd/`, enter **retrofit mode**:
+
+1. Read the existing GDD file.
+2. Identify which of the 8 required sections are present (scan for section headings).
+   Required sections: Overview, Player Fantasy, Detailed Design/Rules, Formulas,
+   Edge Cases, Dependencies, Tuning Knobs, Acceptance Criteria.
+3. Identify which sections contain only placeholder text (`[To be designed]` or
+   equivalent — blank, a single line, or obviously incomplete).
+4. Present to the user before doing anything:
+   ```
+   ## Retrofit: [System Name]
+   File: design/gdd/[filename].md
+
+   Sections already written (will not be touched):
+   ✓ [section name]
+   ✓ [section name]
+
+   Missing or incomplete sections (will be authored):
+   ✗ [section name] — missing
+   ✗ [section name] — placeholder only
+   ```
+5. Ask: "Shall I fill the [N] missing sections? I will not modify any existing content."
+6. If yes: proceed to **Phase 2 (Gather Context)** as normal, but in **Phase 3**
+   skip creating the skeleton (file already exists) and in **Phase 4** skip
+   sections that are already complete. Only run the section cycle for missing/
+   incomplete sections.
+7. **Never overwrite existing section content.** Use Edit tool to replace only
+   `[To be designed]` placeholders or empty section bodies.
+
+If NOT in retrofit mode, normalize the system name to kebab-case for the
+filename (e.g., "combat system" becomes `combat-system`).
 
 ---