refine: Tighten review skill — fail-fast ref check, single-sourced rules, no-op cuts

- Validate the fixed point resolves and diff is non-empty before spawning sub-agents
- Single-source the tooling-enforced and two-axis rationale (point to Why two axes)
- Fix rerank contradiction: summarize worst issue per axis, not across axes
- Drop dead "Read X, then read the diff" preambles from both briefs

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

skills/in-progress/review/SKILL.md

@@ -22,6 +22,8 @@ Whatever the user said is the fixed point — a commit SHA, branch name, tag, `m
 
 Capture the diff command once: `git diff <fixed-point>...HEAD` (three-dot, so the comparison is against the merge-base). Also note the list of commits via `git log <fixed-point>..HEAD --oneline`.
 
+Before going further, confirm the fixed point resolves (`git rev-parse <fixed-point>`) and the diff is non-empty. A bad ref or empty diff should fail here — not inside two parallel sub-agents.
+
 ### 2. Identify the spec source
 
 Look for the originating spec, in this order:
@@ -33,16 +35,7 @@ Look for the originating spec, in this order:
 
 ### 3. Identify the standards sources
 
-Anything in the repo that documents how code should be written. Common locations:
-
-- `CLAUDE.md`, `AGENTS.md`
-- `CONTRIBUTING.md`
-- `CONTEXT.md`, `CONTEXT-MAP.md`, per-context `CONTEXT.md` files
-- `docs/adr/` (architectural decisions are standards)
-- `.editorconfig`, `eslint.config.*`, `biome.json`, `prettier.config.*`, `tsconfig.json` (machine-enforced standards — note them but don't re-check what tooling already checks)
-- Any `STYLE.md`, `STANDARDS.md`, `STYLEGUIDE.md`, or similar at the repo root or under `docs/`
-
-Collect the list of files. The **Standards** sub-agent will read them.
+Anything in the repo that documents how code should be written, such as `CODING_STANDARDS.md` or `CONTRIBUTING.md`.
 
 ### 4. Spawn both sub-agents in parallel
 
@@ -52,21 +45,21 @@ Send a single message with two `Agent` tool calls. Use the `general-purpose` sub
 
 - The full diff command and commit list.
 - The list of standards-source files you found in step 3.
-- The brief: "Read the standards docs. Then read the diff. Report — per file/hunk where relevant — every place the diff violates a documented standard. Cite the standard (file + the rule). Distinguish hard violations from judgement calls. Skip anything tooling enforces. Under 400 words."
+- The brief: "Report — per file/hunk where relevant — every place the diff violates a documented standard. Cite the standard (file + the rule). Distinguish hard violations from judgement calls. Skip anything tooling enforces. Under 400 words."
 
 **Spec sub-agent prompt** — include:
 
 - The diff command and commit list.
 - The path or fetched contents of the spec.
-- The brief: "Read the spec. Then read the diff. Report: (a) requirements the spec asked for that are missing or partial; (b) behaviour in the diff that wasn't asked for (scope creep); (c) requirements that look implemented but where the implementation looks wrong. Quote the spec line for each finding. Under 400 words."
+- The brief: "Report: (a) requirements the spec asked for that are missing or partial; (b) behaviour in the diff that wasn't asked for (scope creep); (c) requirements that look implemented but where the implementation looks wrong. Quote the spec line for each finding. Under 400 words."
 
 If the spec is missing, skip the Spec sub-agent and note this in the final report.
 
 ### 5. Aggregate
 
-Present the two reports under `## Standards` and `## Spec` headings, verbatim or lightly cleaned. Do **not** merge or rerank findings — the two axes are deliberately separate so the user can see them independently.
+Present the two reports under `## Standards` and `## Spec` headings, verbatim or lightly cleaned. Do **not** merge or rerank findings — the two axes are deliberately separate (see *Why two axes*).
 
-End with a one-line summary: total findings per axis, and the worst single issue (if any) flagged.
+End with a one-line summary: total findings per axis, and the worst issue _within each axis_ (if any). Don't pick a single winner across axes — that's the reranking the separation exists to prevent.
 
 ## Why two axes