docs: Chunk 3 issues 0015-0028 and doc updates

14 issues created covering AGENTS.md refactor prerequisite, skill
implementation workflow grill, bootstrap skills (write-eval, write-skill),
remaining factory skills, and one issue per skill category group through
to chunk closure. All HITL; acceptance criteria for 0017-0028 to be
refined after 0016 grill session.

Doc updates: CONTEXT.md PRD/issue scope clarified (HOW distribution
across architecture-review and issue design notes); ROADMAP.md housekeeping
updated with bootstrap order and issue range; spec/overview.md recent
changes entry added; PRD updated (skills-index: delete → update).

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

docs/issues/0021-implement-skills.md

@@ -0,0 +1,53 @@
+# 0021 — Implement skills: implement-feature, tdd, refactor, write-docs, diagnose
+
+**Type:** HITL  
+**Parent PRD:** `docs/prd/chunk-3-skills-library.md`
+
+## What to build
+
+The 5 implement phase skills. Two are new; three are preserved Pocock placeholders upgraded to the authoring standard. All authored via `write-skill` (0018), evals via `write-eval` (0017).
+
+**Skills, origins, and trigger descriptions:**
+
+| Flat name | Origin | Trigger description |
+|---|---|---|
+| `implement-feature` | New | Implement a feature, build this, write the code for X |
+| `tdd` | Preserved; frontmatter + standard added | TDD, test-driven, red-green-refactor |
+| `refactor` | New | Refactor this code, improve structure, clean up |
+| `write-docs` | New | Write documentation, add docstrings, generate README |
+| `diagnose` | Preserved; frontmatter + standard added | Diagnose this, what's wrong with X, debug this |
+
+**Key constraints per skill:**
+- `implement-feature`: must start from a linked issue with an EARS spec (checks `docs/issues/` in the file-based phase, Gitea MCP when configured); flags if none exists; no unrequested abstractions; updates `docs/spec/` as part of implementation if behaviour changes; calls `tdd` as its implementation methodology
+- `tdd`: composable and separate from `implement-feature` so TDD can be used outside full feature implementation; red-green-refactor loop
+- `refactor`: preserves all existing behaviour; documents what changed and why
+- `write-docs`: derives from code and spec; never invents behaviour
+- `diagnose`: preserved behavior; add frontmatter, authoring standard sections, and dead-reference cleanup
+
+## Implementation notes
+
+Follow the per-skill workflow defined in `docs/notes/skill-implementation-workflow.md` (produced by issue 0016).
+
+**Known upstream sources to review for this category:**
+- `mattpocock/skills` — original `tdd` and `diagnose` placeholders; review at current HEAD; record SHAs in `source:` for any adopted content
+- `bmad-method/bmad-method` — BMAD developer role and implementation patterns; relevant for `implement-feature` and `refactor`
+
+For new skills (`implement-feature`, `refactor`, `write-docs`): search for prior art in the above repos before writing from scratch.
+
+## Acceptance criteria
+
+- [ ] All 5 SKILL.md files exist at `.agents/skills/<skill-name>/SKILL.md`; `metadata.category: implement`; authoring standard met
+- [ ] Dead references removed from Pocock skills (`tdd`, `diagnose`)
+- [ ] `implement-feature` checks for linked issue with EARS spec before proceeding; calls `tdd` by name
+- [ ] `source:` fields populated for adopted upstream content
+- [ ] Each skill has a co-located eval at `.agents/evals/implement/<skill-name>/eval.yaml` via `write-eval`
+- [ ] `install.sh` deploys all 5 to `~/.agents/skills/`
+- [ ] **HITL:** human runs behavioral test per skill
+- [ ] **HITL:** human reviews each SKILL.md and eval before committing
+- [ ] _(Further criteria to be refined after issue 0016 grill session)_
+
+## Blocked by
+
+- 0016 (per-skill workflow)
+- 0017 (`write-eval`)
+- 0018 (`write-skill`)