feat(pr): Add structured PR body skill

.claude/skills/pr-ready/SKILL.md

@@ -0,0 +1,170 @@
+---
+name: pr-ready
+description: "Use when writing or updating a PR body. Produces Summary (visual), Evidence (before/after), and Merge Danger (door + blast radius) sections."
+metadata:
+  credits:
+    skill: show-me
+    author: Dex Horthy
+    organisation: Humanlayer
+    url: "https://github.com/humanlayer/skills/blob/main/plugins/show-me/skills/show-me/SKILL.md"
+---
+
+Use this template for writing the PR body:
+
+```markdown
+## Summary
+
+<diagram, diff-sketch, or tree>
+
+## Evidence
+
+- **Before:** <screenshot/output/failing test run>
+  **After:** <screenshot/output/passing test run>
+
+## Merge Danger
+
+**Door:** <one-way or two-way>
+
+<optional: description>
+
+**Blast Radius:** <one-word description>
+
+<optional: potential ramifications of merge>
+```
+
+## Sections
+
+Skip all preambles and keep prose brief. Use the user's domain language from `GLOSSARY.md`.
+
+### Summary
+
+Pick the smallest view that makes the key point clear.
+
+- Show logic or an algorithm as pseudocode:
+
+```text
+on(save)
+  if content is unchanged
+    return cached result
+  write new content
+  return fresh result
+```
+
+- Show runtime control flow as a call tree:
+
+```text
+submitForm
+  createSession
+    persistPrompt
+    launchAgent
+  navigateToSession
+```
+
+- Show UI structure as a component tree, including state and module boundaries that matter:
+
+```text
+<SessionPage> (apps/example/src/routes/session.tsx)
+  useSessionEvents()
+  <SessionToolbar>
+    <RunSkillButton> (packages/ui)
+```
+
+- Show file responsibility or a broad refactor as a shallow file tree:
+
+```text
+src/
+├── commands/       # parses user actions
+├── sessions/       # owns session state
+└── transport/      # sends API requests
+```
+
+- Show component interaction, control flow, or data flow with Mermaid:
+
+```mermaid
+sequenceDiagram
+    participant User
+    participant UI
+    participant Daemon
+    User->>UI: choose command
+    UI->>Daemon: send expanded prompt
+    Daemon-->>UI: stream result
+```
+
+- Use `diff` when the point is what changes and the surrounding shape already exists. Match the diff shape to the topic.
+
+For a component change:
+
+```diff
+ <SessionPage>
+   useSessionEvents()
+   <SessionToolbar>
++    <RunSkillButton />
+   <SessionTimeline>
++    <SkillResultCard />
+```
+
+For a file-layout change:
+
+```diff
+ src/
+ ├── commands/
++│   └── show-me.ts       # expands the slash command
+ ├── sessions/
+-└── transport.ts
++└── transport/
++    ├── client.ts
++    └── stream.ts
+```
+
+For a call-tree or call-stack change:
+
+```diff
+ submitForm
+   createSession
+     persistPrompt
++    expandSkillMention
+     launchAgent
+-  navigateToSession
++  navigateToSession
++    subscribeToEvents
+```
+
+For a state or control-flow change:
+
+```diff
+ on(save)
+-  write content
++  if content is unchanged
++    return cached result
++  write new content
++  invalidate cache
+```
+
+- Show the whole block when most of it is new, when omitted context would hide ownership or order, or when the user needs a copyable target shape:
+
+```ts
+function expandSkill(command: string): string {
+  const skillName = command.slice(1);
+  return `use the ${skillName} skill`;
+}
+```
+
+#### Guidance
+
+Place each visual next to the short text it supports. Keep only the calls, files, props, states, and boundaries needed to answer the user's current question or the options to resolve the current discussion point.
+
+You may use one of these, you may use several, it is unlikely you will use all of them. Use your judgement and don't overwhelm the user.
+
+### Evidence
+
+Concrete evidence that the change works. Show a before and after.
+
+Screenshots are S-tier - when the environment is set up for it and the change is visual.
+
+Execution-based evidence is A-tier. Test results, console output. Show the exact test that now fails and passes, using pseudocode.
+
+### Merge Danger
+
+Describe whether it's a one-way or two-way door. You can walk back through two-way doors, but not one-way doors. A PR that is cheap to roll back is lower risk. Changes that involve destructive actions or hard-to-reverse decisions are one-way doors.
+
+The blast radius is the potential impact or scope of the changes introduced by this PR. Consider all possibilities. Examples are layout shift, breakages for consumers, mobile responsiveness, etc.

.github/workflows/pr-ready.yml

@@ -0,0 +1,129 @@
+# Rewrite PR body with Claude (pr-ready skill) on ready-for-review label.
+name: PR Ready Body
+
+on:
+  pull_request:
+    types: [labeled]
+
+permissions:
+  contents: read
+  pull-requests: write
+
+concurrency:
+  group: pr-ready-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
+jobs:
+  rewrite-body:
+    if: >-
+      github.event.label.name == 'ready-for-review' &&
+      github.actor != 'dependabot[bot]' &&
+      github.event.pull_request.head.repo.full_name == github.repository
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - name: Checkout (skill + PR template only)
+        uses: actions/checkout@v7
+        with:
+          sparse-checkout: |
+            .claude/skills/pr-ready/SKILL.md
+            .github/pull_request_template.md
+          sparse-checkout-cone-mode: false
+          persist-credentials: false
+
+      - name: Rewrite PR body with Claude
+        uses: actions/github-script@v9
+        env:
+          ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
+        with:
+          script: |
+            const fs = require('fs');
+            const pr = context.payload.pull_request;
+
+            if (!process.env.ANTHROPIC_API_KEY) {
+              core.setFailed('ANTHROPIC_API_KEY secret is not set');
+              return;
+            }
+
+            const skill = fs.readFileSync('.claude/skills/pr-ready/SKILL.md', 'utf8');
+            const template = fs.readFileSync('.github/pull_request_template.md', 'utf8');
+
+            const { data: rawDiff } = await github.rest.pulls.get({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              pull_number: pr.number,
+              mediaType: { format: 'diff' },
+            });
+            // Cap huge diffs (lockfiles, fixtures) to fit context.
+            const DIFF_CHAR_CAP = 400000;
+            const diff = rawDiff.length > DIFF_CHAR_CAP
+              ? rawDiff.slice(0, DIFF_CHAR_CAP) + '\n\n[diff truncated]'
+              : rawDiff;
+
+            const prompt = `You are rewriting the body of a GitHub pull request.
+
+            Follow the skill below exactly. Keep the repository PR template's sections (## Issue, ## Checklist, ## Notes) and fill them from the current body; replace the template's ## Summary with the skill's three sections (## Summary, ## Evidence, ## Merge Danger) in that order, between ## Issue and ## Checklist. Keep any "Closes ..." issue reference verbatim; if none, write "Closes #PLEASE_TYPE_ISSUE_NUMBER". Preserve checklist [x]/[ ] states from the current body. Do not invent evidence: only cite tests, numbers or screenshots present in the current body or diff. Output ONLY the markdown body.
+
+            <skill>
+            ${skill}
+            </skill>
+
+            <pull_request_template>
+            ${template}
+            </pull_request_template>
+
+            PR title: ${pr.title}
+            Branch: ${pr.head.ref} -> ${pr.base.ref}
+
+            <current_body>
+            ${pr.body || '(empty)'}
+            </current_body>
+
+            <diff>
+            ${diff}
+            </diff>`;
+
+            const response = await fetch('https://api.anthropic.com/v1/messages', {
+              method: 'POST',
+              headers: {
+                'Content-Type': 'application/json',
+                'x-api-key': process.env.ANTHROPIC_API_KEY,
+                'anthropic-version': '2023-06-01',
+                'anthropic-beta': 'server-side-fallback-2026-07-01',
+              },
+              body: JSON.stringify({
+                model: 'claude-opus-5-5',
+                max_tokens: 8000,
+                fallbacks: 'default',
+                output_config: { effort: 'medium' },
+                messages: [{ role: 'user', content: prompt }],
+              }),
+            });
+
+            const data = await response.json();
+            if (!response.ok) {
+              core.setFailed(`Anthropic API error: ${JSON.stringify(data)}`);
+              return;
+            }
+            if (data.stop_reason === 'refusal') {
+              core.setFailed(`Claude declined the request: ${JSON.stringify(data.stop_details)}`);
+              return;
+            }
+
+            const body = data.content
+              .filter((block) => block.type === 'text')
+              .map((block) => block.text)
+              .join('')
+              .trim();
+            if (!body) {
+              core.setFailed('Empty response from Claude');
+              return;
+            }
+
+            const original = pr.body || '(empty)';
+            await github.rest.pulls.update({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              pull_number: pr.number,
+              body: `${body}\n\n<details><summary>Previous PR description</summary>\n\n${original}\n\n</details>`,
+            });