docs: issue 0016 — skill implementation workflow grill

Produces docs/notes/skill-implementation-workflow.md with agreed conventions
for all Chunk 3 skill issues (0017–0028). Key decisions:

- Per-skill process: source discovery (sub-agent) → source review with
  licence/security check (sub-agent) → conflict check vs constitution +
  factory principles (sub-agent) → synthesis grill → co-write iteratively
- Bootstrap: write-eval (hand-written) → write-skill (hand-written) →
  write-docs (first factory-authored, phase 2 of 0018) → everything else
- Upstream review changed from per-chunk-start to per-skill
- `when:` and `references:` frontmatter fields added to authoring standard
- Sub-agent usage prescribed as named steps in the workflow
- HITL: human reviewed and approved conventions

Updates: PRD implementation decisions; issues 0016–0028 with specific
acceptance criteria; docs/spec/overview.md; ROADMAP Chunk 3 housekeeping note
(bootstrap order, cadence, acceptance criteria status); CONTEXT.md Source field
(per-skill cadence, references: companion field); LESSONS.md with three patterns
from the grill session.

Post-grill additions (same session): Step 6 (session handoff) added to the
workflow; handoff section appended to issue 0016; handoff checklist item added
to Chunk 3 closure issue (0028).

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

docs/issues/0028-chunk-3-closure.md

@@ -17,6 +17,7 @@ Close out Chunk 3 once all 42 skills are complete: update the skills index to re
 **Behavioral test scope:** All 42 skills (including `write-eval`, `write-skill`, and the 4 preserved skills). The `caveman` skill is exempt — it has no content-generating behavior to verify.
 
 **LESSONS.md:** Extract any cross-session learnings from Chunk 3 implementation and add entries per the LESSONS.md format. Three or more observations on the same pattern graduate to the relevant standing file.
+6. Review `docs/notes/skill-implementation-workflow.md` — verify the conventions are still accurate; update any entries that changed during implementation.
 
 ## Acceptance criteria
 
@@ -26,6 +27,8 @@ Close out Chunk 3 once all 42 skills are complete: update the skills index to re
 - [ ] `docs/ROADMAP.md` Chunk 3 row updated to ✅
 - [ ] Behavioral test run completed; all skills pass their trigger test; failures documented as issues for resolution
 - [ ] `LESSONS.md` updated with Chunk 3 observations
+- [ ] `docs/notes/skill-implementation-workflow.md` reviewed and updated to reflect any workflow changes discovered during Chunk 3
+- [ ] All skill issues (0017–0027) have a `## Handoff` section with status `complete`
 - [ ] **HITL:** human verifies the complete skills library in a fresh session before marking Chunk 3 done
 
 ## Blocked by