Add setup-matt-pocock-skills; rename github-triage to triage; migrate engineering skills to vague prose

Engineering skills no longer hard-code GitHub or specific label strings.
A new setup skill scaffolds an `## Agent skills` block in
AGENTS.md/CLAUDE.md plus `docs/agents/` so each repo can declare its own
backlog backend, triage label vocabulary, and domain doc layout. Skills
that need the mapping (to-issues, to-prd, triage) point at the setup
skill; skills that only soften with it (diagnose, tdd,
improve-codebase-architecture, zoom-out) stay vague. ADR-0001 records
the split.

Closes #88, #89.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

skills/engineering/triage/AGENT-BRIEF.md

@@ -0,0 +1,168 @@
+# Writing Agent Briefs
+
+An agent brief is a structured comment posted on a GitHub issue when it moves to `ready-for-agent`. It is the authoritative specification that an AFK agent will work from. The original issue body and discussion are context — the agent brief is the contract.
+
+## Principles
+
+### Durability over precision
+
+The issue may sit in `ready-for-agent` for days or weeks. The codebase will change in the meantime. Write the brief so it stays useful even as files are renamed, moved, or refactored.
+
+- **Do** describe interfaces, types, and behavioral contracts
+- **Do** name specific types, function signatures, or config shapes that the agent should look for or modify
+- **Don't** reference file paths — they go stale
+- **Don't** reference line numbers
+- **Don't** assume the current implementation structure will remain the same
+
+### Behavioral, not procedural
+
+Describe **what** the system should do, not **how** to implement it. The agent will explore the codebase fresh and make its own implementation decisions.
+
+- **Good:** "The `SkillConfig` type should accept an optional `schedule` field of type `CronExpression`"
+- **Bad:** "Open src/types/skill.ts and add a schedule field on line 42"
+- **Good:** "When a user runs `/triage` with no arguments, they should see a summary of issues needing attention"
+- **Bad:** "Add a switch statement in the main handler function"
+
+### Complete acceptance criteria
+
+The agent needs to know when it's done. Every agent brief must have concrete, testable acceptance criteria. Each criterion should be independently verifiable.
+
+- **Good:** "Running `gh issue list --label needs-triage` returns issues that have been through initial classification"
+- **Bad:** "Triage should work correctly"
+
+### Explicit scope boundaries
+
+State what is out of scope. This prevents the agent from gold-plating or making assumptions about adjacent features.
+
+## Template
+
+```markdown
+## Agent Brief
+
+**Category:** bug / enhancement
+**Summary:** one-line description of what needs to happen
+
+**Current behavior:**
+Describe what happens now. For bugs, this is the broken behavior.
+For enhancements, this is the status quo the feature builds on.
+
+**Desired behavior:**
+Describe what should happen after the agent's work is complete.
+Be specific about edge cases and error conditions.
+
+**Key interfaces:**
+- `TypeName` — what needs to change and why
+- `functionName()` return type — what it currently returns vs what it should return
+- Config shape — any new configuration options needed
+
+**Acceptance criteria:**
+- [ ] Specific, testable criterion 1
+- [ ] Specific, testable criterion 2
+- [ ] Specific, testable criterion 3
+
+**Out of scope:**
+- Thing that should NOT be changed or addressed in this issue
+- Adjacent feature that might seem related but is separate
+```
+
+## Examples
+
+### Good agent brief (bug)
+
+```markdown
+## Agent Brief
+
+**Category:** bug
+**Summary:** Skill description truncation drops mid-word, producing broken output
+
+**Current behavior:**
+When a skill description exceeds 1024 characters, it is truncated at exactly
+1024 characters regardless of word boundaries. This produces descriptions
+that end mid-word (e.g. "Use when the user wants to confi").
+
+**Desired behavior:**
+Truncation should break at the last word boundary before 1024 characters
+and append "..." to indicate truncation.
+
+**Key interfaces:**
+- The `SkillMetadata` type's `description` field — no type change needed,
+  but the validation/processing logic that populates it needs to respect
+  word boundaries
+- Any function that reads SKILL.md frontmatter and extracts the description
+
+**Acceptance criteria:**
+- [ ] Descriptions under 1024 chars are unchanged
+- [ ] Descriptions over 1024 chars are truncated at the last word boundary
+      before 1024 chars
+- [ ] Truncated descriptions end with "..."
+- [ ] The total length including "..." does not exceed 1024 chars
+
+**Out of scope:**
+- Changing the 1024 char limit itself
+- Multi-line description support
+```
+
+### Good agent brief (enhancement)
+
+```markdown
+## Agent Brief
+
+**Category:** enhancement
+**Summary:** Add `.out-of-scope/` directory support for tracking rejected feature requests
+
+**Current behavior:**
+When a feature request is rejected, the issue is closed with a `wontfix` label
+and a comment. There is no persistent record of the decision or reasoning.
+Future similar requests require the maintainer to recall or search for the
+prior discussion.
+
+**Desired behavior:**
+Rejected feature requests should be documented in `.out-of-scope/<concept>.md`
+files that capture the decision, reasoning, and links to all issues that
+requested the feature. When triaging new issues, these files should be
+checked for matches.
+
+**Key interfaces:**
+- Markdown file format in `.out-of-scope/` — each file should have a
+  `# Concept Name` heading, a `**Decision:**` line, a `**Reason:**` line,
+  and a `**Prior requests:**` list with issue links
+- The triage workflow should read all `.out-of-scope/*.md` files early
+  and match incoming issues against them by concept similarity
+
+**Acceptance criteria:**
+- [ ] Closing a feature as wontfix creates/updates a file in `.out-of-scope/`
+- [ ] The file includes the decision, reasoning, and link to the closed issue
+- [ ] If a matching `.out-of-scope/` file already exists, the new issue is
+      appended to its "Prior requests" list rather than creating a duplicate
+- [ ] During triage, existing `.out-of-scope/` files are checked and surfaced
+      when a new issue matches a prior rejection
+
+**Out of scope:**
+- Automated matching (human confirms the match)
+- Reopening previously rejected features
+- Bug reports (only enhancement rejections go to `.out-of-scope/`)
+```
+
+### Bad agent brief
+
+```markdown
+## Agent Brief
+
+**Summary:** Fix the triage bug
+
+**What to do:**
+The triage thing is broken. Look at the main file and fix it.
+The function around line 150 has the issue.
+
+**Files to change:**
+- src/triage/handler.ts (line 150)
+- src/types.ts (line 42)
+```
+
+This is bad because:
+- No category
+- Vague description ("the triage thing is broken")
+- References file paths and line numbers that will go stale
+- No acceptance criteria
+- No scope boundaries
+- No description of current vs desired behavior