refactor(skills): retrofit the corpus to the ADR-0020 context contract (#129)

Retrofits all 39 skills to ADR-0020's description/body context contract, then fixes what six rounds of independent review found in that retrofit — including four ways the hot gate itself failed open.

Closes #99, #107, #108, #110, #111, #114, #115, #120.

## The retrofit (waves 1-5)

| | Start | Now |
|---|---|---|
| Description FAILs (>400 chars) | 26 | **0** |
| Body FAILs (>900 words, body-only) | 9 | **0** |
| Dangling routing targets | 2 | **0** |
| `Kyberforge.CompositionNote` | 10 | **0** |
| Preload tax | 21,005 chars | **~10,500** |

Under the 12,000-char success criterion. Per-wave detail is on #99.

## The review fixes

**The gate failed open four ways, three of them found after the retrofit shipped.** An unrecognised follower token made a dangling target vanish. A skill directory with no `SKILL.md` resolved as a valid target, so a commit could be green locally and red in a fresh clone — three existing fixtures were relying on that, one of which made the install-leak A/B pass vacuously. Then the free-standing `/name` sweep turned out to be gated on the sentence carrying a boundary marker, so route notation in any other sentence was invisible — not an ERROR, not a SUGGESTION, not an INFO — which left the documented "`/name` always blocks" promise false from a second direction. All four fixed and pinned.

**Two checks were silently not running.** `validate-provenance.sh` checks 7-8 were dead across nine skills. Waking them exposed a deeper problem: they assume `Research doc:` names a source index, but 30 of 121 entries point at topic content documents, so every new check-7 INFO was a false positive and check 8 was saved from a false-FAIL flood only by an *unannounced* skip. Checks 7/8 are now scoped to source indexes and every skip announces itself (#121).

**The retrofit's own anti-goal, four times.** ADR-0020 warns that a blunt gate gets satisfied by deleting content rather than relocating it. `diagnose` and `skill-audit` relocated prose and then read it unconditionally; `prototype` and `vale-config` deleted rules outright that survived nowhere. All four addressed.

## Verification

- `bash tests/run-tests.sh --strict` — 24 suites, 0 skipped, 0 failed
- `bash tests/run-bats.sh` — 325 tests, 0 failures
- `pre-commit run --all-files` — 17/17
- `pre-commit run --hook-stage pre-push --all-files` — 16/16, with `apm marketplace check` and `apm pack --check-clean` run against the remote, not skipped
- `scripts/skill-size-check.sh` over all 39 skills — rc 0, 0 ERROR/FAIL, SUGGESTION-only
- Preload tax measured at **10,498 chars**, max description 390 — both inside budget
- Every new test proven non-vacuous by a deliberate mutation of the behaviour it covers

**Per-commit sync, stated accurately:** the ten commits from the latest review round each pass `check-plugin-content-sync` in isolation, verified by checking each out in a detached worktree with a clean between. The earlier gitea window (`dfacf05..bedbd1d`, nine commits) does **not** — its mirror was regenerated in one batch at `bbc7300`. An earlier revision of this description claimed the property held for every commit; it does not, and a bisect through that window lands on a red commit. **Squash-merge** to collapse it, or accept that this range is not bisectable.

## Version bump

Six plugins and the catalog take a **patch**, not a minor. The branch is **89 commits — 40 `fix` / 30 `refactor` / 12 `docs` / 5 `chore` / 2 `test` — zero `feat`, zero `!`, zero `BREAKING CHANGE`** — and adds no skill, agent, command or hook. (Two earlier revisions of this section cited a stale histogram, most recently 78 commits; the figures above are measured at HEAD.) Both rules this repo ships (`forge/references/version-bump.md`, landing in this PR, and `git-commits/references/conventional-commits-spec.md`) make that a patch, and the catalog set is unchanged at 7 entries.

Not settled by that: four published files were removed from the installed tree, three moved, and `caveman` gained `disable-model-invocation`, retiring its old triggers. Under a strict reading those are major-class and currently ship under `refactor:` with no marker. Whether the deployed skill surface is a public contract is written down nowhere — worth deciding, but it outlives this PR.

## Deliberately not in scope

#112 (cherry-pick ownership, now resolved in favour of `git-commits`), #113 (`rtk git` normalisation), #116 (research fan-out), #101 (audit-skill merge), #122 (non-spec skill-root files), #123 (no PRD producer) stay open. #117 is the one worth reading: the contract's remedy is to move prose into `references/`, which is exactly where neither the size gate nor Vale looks — and the blind spot is wider than #117 currently records, since there is no root `.vale.ini` at all, so every ADR, `CONTEXT.md` and `README.md` is unlinted too.

That blind spot let this branch carry two `level: error` `Kyberforge.SentenceOpenerThereIs` violations into `references/` files it created — `provider-adapter-author/references/provider-matrix.md:31` and `agent-audit/references/finding-criteria.md:95`. Both are reworded in `afadaae`, confirmed by routing each file through the audit's own `vale-wrap.sh` (1 error each before, 0 after). Five further occurrences sit in `references/` files already on `main`; those are the pre-existing corpus and stay with #117, which is the real fix.

Also unfixed and not this PR's: `apm install` appends a duplicate `SessionStart` entry to `.claude/settings.json`, so a fresh clone cannot get pre-push green without an edit AGENTS.md warns against. Reproduces identically on `main`.

Co-authored-by: Defame1297 <gitea@rkdr.net>
Reviewed-on: https://git.dev.rkdr.net/Defame1297/holocron/pulls/129
Co-authored-by: Claude Code AI - Gitea MCP <claude@noreply.git.dev.rkdr.net>
Co-committed-by: Claude Code AI - Gitea MCP <claude@noreply.git.dev.rkdr.net>

plugins/core/skills/provider-adapter-author/references/provider-matrix.md

@@ -0,0 +1,32 @@
+---
+source_keys:
+  - adr-0002-0003-two-tier-claude-md
+---
+
+# Known provider instruction files
+
+Which files to look for when detecting a provider-specific instruction file, whether each provider
+resolves a cross-file import, and what a thin adapter therefore looks like for it.
+
+| Provider | File(s) | Import syntax | Thin adapter shape | Validator flag |
+|---|---|---|---|---|
+| Claude Code | `CLAUDE.md` at the repo root, plus any deployed copies | Yes — `@path` lines, e.g. `@AGENTS.md` | One or more `@` import lines; no other content is required | none |
+| Cursor | `.cursor/rules/*.mdc` | No | A short sentence pointing at `AGENTS.md`, plus the rule's own frontmatter and provider-specific body | `--no-import-syntax` |
+| GitHub Copilot | `.github/copilot-instructions.md` | No | A short sentence pointing at `AGENTS.md`, plus Copilot-only instructions | `--no-import-syntax` |
+| Anything else | tool-specific instruction file at whatever path the tool documents | Assume no | Text pointer, as above | `--no-import-syntax` |
+
+A provider not listed here is not evidence it has an import mechanism. Confirm against that tool's
+own documentation before emitting an `@`-style line; an unresolved import reads as literal text and
+silently drops every rule the adapter was supposed to defer to.
+
+Detection is a search, not a lookup: a repo may hold more than one of these, and each one converts
+independently against the same `AGENTS.md`.
+
+## Standalone and composed runs behave identically
+
+This skill is reached two ways: invoked directly by a user, and composed into by `agentsmd-author`
+once it has written or updated the repo's `AGENTS.md`. Behave identically either way — do not
+assume a caller skill exists. Detect the provider file yourself, confirm `AGENTS.md` yourself, and
+run the closeout validator yourself, rather than treating any step as already done by the caller or
+as something the caller will do afterwards. No handshake exists to rely on, and no state is
+passed in beyond the file paths.

plugins/core/skills/provider-adapter-author/references/sources.md

@@ -5,5 +5,5 @@
 - **URL:** (in-repo precedent — not an external source or plugin research corpus entry)
 - **Description:** This repo's own two-tier CLAUDE.md/AGENTS.md pattern: AGENTS.md is the provider-agnostic source of always-on rules; provider-specific files (CLAUDE.md) become thin adapters that import it (`@AGENTS.md` plus provider-specific additions). Grounds this skill's entire adapter-conversion design — the "thin adapter" shape, the `@`-import convention, and the size/duplication expectations enforced by `scripts/validate-adapter.sh`.
 - **Research doc:** docs/adr/0002-two-tier-claude-md.md, docs/adr/0003-agents-md-provider-agnostic-entry-point.md, providers/claude-code/CLAUDE.md (in-repo ADRs and a live example, not a plugin research corpus entry; referenced here since this skill's design is modeled directly on an existing implementation rather than external research)
-- **Contributing files:** SKILL.md
+- **Contributing files:** SKILL.md, references/provider-matrix.md
 - **Status:** `extracted`