fix: write-skill governance review — model field, eval self-check, grill wiring

- Add model: sonnet to SKILL.md frontmatter (Claude Code extension; correct
  location per research — runtime config belongs in frontmatter, not META.md)
- Document model field in SKILL-TEMPLATE.md with factory §9 routing guidance
- Wire grill output explicitly to trigger description step (step 3 now references
  agreed name/category/purpose from grill rather than drafting independently)
- Strengthen eval self-check: presence check → coverage check (trigger cases +
  at least one output case required)
- Bump META.md to v1.2 (2026-05-26)
- Add three LESSONS.md entries: META-TEMPLATE comment retention, overlap check
  scope (deployed dir not just repo), model field placement boundary

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

LESSONS.md

@@ -70,6 +70,18 @@ When a skill produces a structured artifact like SKILL.md, the natural approach
 
 The agent-level HITL rule ("require explicit confirmation before irreversible shared-state operations") is being bypassed: the agent calls the tool and lets the permission dialog catch it. This means the rule is not firing in agent reasoning — it's the permission system acting as a safety net. If a user selects "don't ask again," the net disappears. Fix: the HITL rule needs to be framed as "do not call the tool" rather than "ask before proceeding" — the agent must ask first, then act only after explicit confirmation.
 
+## 2026-05-26 — META-TEMPLATE uses YAML comments; META.md output retains them
+
+META-TEMPLATE.md uses YAML `#` comments to explain fields inline. SKILL-TEMPLATE.md uses HTML comments inside XML tags, which the agent strips on fill. The structural difference means SKILL.md output is clean but META.md output retains the explanatory `#` lines — an inconsistency. Fix: restructure META-TEMPLATE.md so all explanatory guidance is prose above the code block (markdown, never copied into the output YAML), and the code block itself uses `<placeholder>` syntax with no `#` comment lines. This makes META.md fill behaviour deterministic for the same reason SKILL.md fill is: `<...>` markers are unambiguously replaceable; prose above the block is not part of the template.
+
+## 2026-05-26 — Overlap checks must scan the deployed directory, not just the source repo
+
+`write-a-skill` existed only in `~/.agents/skills/` (installed from a pre-refactor source) and was invisible during a repo-level scan of `.agents/skills/`. Governance reviews and overlap checks that only look at the source repo will miss skills added by install.sh from other sources or prior runs. Fix: overlap checks must scan the deployed `~/.agents/skills/` directory, not just the repo's `.agents/skills/`.
+
+## 2026-05-26 — `model:` field belongs in SKILL.md frontmatter, not META.md
+
+Claude Code supports `model:` as a provider extension in SKILL.md frontmatter — it overrides the session model for the skill's turn and reverts after. Attempting to put it in META.md was wrong: META.md is provenance/audit metadata, not runtime config. The boundary: if a field affects agent behaviour at invocation time, it belongs in SKILL.md frontmatter; if it serves upgrade reviews and audit trails, it belongs in META.md.
+
 ## 2026-05-18 — Planning meta-commentary does not belong in deployed artifacts
 
 During write-skill refactor, an "open thread" note (about a deferred research step) was written directly into the SKILL.md Process section. The user caught it. The rule it violated: a deployed artifact (SKILL.md, a runtime file loaded by agents) must not contain planning meta-commentary — deferred items, open threads, and implementation notes belong in the issue file, which is the planning artifact. The skill body should contain only content relevant to runtime execution. If a decision is deferred, record it in the issue and leave no trace in the skill. The distinction: issue = planning record; skill = executable instruction.