Replace subagent review loops with lightweight inline self-review

The subagent review loop (dispatching a fresh agent to review plans/specs)
doubled execution time (~25 min overhead) without measurably improving plan
quality. Regression testing across 5 versions (v3.6.0 through v5.0.4) with
5 trials each showed identical plan sizes, task counts, and quality scores
regardless of whether the review loop ran.

Changes:
- writing-plans: Replace subagent Plan Review Loop with inline Self-Review
  checklist (spec coverage, placeholder scan, type consistency)
- writing-plans: Add explicit "No Placeholders" section listing plan failures
  (TBD, vague descriptions, undefined references, "similar to Task N")
- brainstorming: Replace subagent Spec Review Loop with inline Spec Self-Review
  (placeholder scan, internal consistency, scope check, ambiguity check)
- Both skills now use "look at it with fresh eyes" framing

Testing: 5 trials with the new skill show self-review catches 3-5 real bugs
per run (spawn positions, API mismatches, seed bugs, grid indexing) in ~30s
instead of ~25 min. Remaining defects are comparable to the subagent approach.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

skills/writing-plans/SKILL.md

@@ -103,26 +103,33 @@ git commit -m "feat: add specific feature"
 ```
 ````
 
+## No Placeholders
+
+Every step must contain the actual content an engineer needs. These are **plan failures** — never write them:
+- "TBD", "TODO", "implement later", "fill in details"
+- "Add appropriate error handling" / "add validation" / "handle edge cases"
+- "Write tests for the above" (without actual test code)
+- "Similar to Task N" (repeat the code — the engineer may be reading tasks out of order)
+- Steps that describe what to do without showing how (code blocks required for code steps)
+- References to types, functions, or methods not defined in any task
+
 ## Remember
 - Exact file paths always
-- Complete code in plan (not "add validation")
+- Complete code in every step — if a step changes code, show the code
 - Exact commands with expected output
-- Reference relevant skills with @ syntax
 - DRY, YAGNI, TDD, frequent commits
 
-## Plan Review Loop
+## Self-Review
 
-After writing the complete plan:
+After writing the complete plan, look at the spec with fresh eyes and check the plan against it. This is a checklist you run yourself — not a subagent dispatch.
 
-1. Dispatch a single plan-document-reviewer subagent (see plan-document-reviewer-prompt.md) with precisely crafted review context — never your session history. This keeps the reviewer focused on the plan, not your thought process.
-   - Provide: path to the plan document, path to spec document
-2. If ❌ Issues Found: fix the issues, re-dispatch reviewer for the whole plan
-3. If ✅ Approved: proceed to execution handoff
+**1. Spec coverage:** Skim each section/requirement in the spec. Can you point to a task that implements it? List any gaps.
 
-**Review loop guidance:**
-- Same agent that wrote the plan fixes it (preserves context)
-- If loop exceeds 3 iterations, surface to human for guidance
-- Reviewers are advisory — explain disagreements if you believe feedback is incorrect
+**2. Placeholder scan:** Search your plan for red flags — any of the patterns from the "No Placeholders" section above. Fix them.
+
+**3. Type consistency:** Do the types, method signatures, and property names you used in later tasks match what you defined in earlier tasks? A function called `clearLayers()` in Task 3 but `clearFullLayers()` in Task 7 is a bug.
+
+If you find issues, fix them inline. No need to re-review — just fix and move on. If you find a spec requirement with no task, add the task.
 
 ## Execution Handoff