feat(lint): expand Vale audit prefilter into a broader plugin-content harness

Deferred item from PR #85 review. Per ADR-0013: cherry-picks two low-noise
rules from trialing write-good/alex against the real corpus (VagueQualifier,
SentenceOpenerThereIs) into styles/Kyberforge rather than adopting either
package wholesale (both are tuned for blog prose and were noisy on this
repo's terse, imperative instruction files - see the ADR's rejected-rule
list). Adds a new skill-size-check pre-commit hook enforcing agentskills.io's
500-line/5,000-token SKILL.md ceiling, currently unenforced. Fixes the 28
resulting violations across 20 existing SKILL.md/agent files so the
enforcing pre-commit hook lands clean.

governance.md/CONTROLS.md were evaluated and excluded as rule sources -
they're org/CI-infrastructure controls, not prose patterns Vale can express.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QUDczvw1H3eEeMD29Q9Lbi

docs/adr/0013-vale-harness-scope-and-rule-sources.md

@@ -0,0 +1,84 @@
+# Vale audit prefilter expands into a plugin-content harness, scoped to prose-pattern rules only
+
+Issue #84 wired Vale as a deterministic prefilter for `skill-audit`/`agent-audit`, scoped to
+exactly four pattern-matchable checks (imperative description opener, vague capability wording,
+generic reference-pointer padding, Copilot's dead `Use proactively` phrasing), documented only in
+CONTEXT.md's "Vale audit prefilter" section — never its own ADR — and explicitly excluding body
+discipline, near-miss exclusion strength, and control calibration as non-goals. This ADR records a
+deferred PR #85 review item to broaden that coverage, retroactively captures #84's own rationale
+(since it was never recorded as a decision in its own right), and layers the expansion on top
+without reversing or weakening the original four rules.
+
+**File scope stays the same.** `SKILL.md` plus agent files (`plugins/*/agents/*.md`,
+`plugins/*/agents/*.agent.md`) only — matching the existing prefilter's globs. Skill-level
+`README.md` files and `plugin.json` manifests are not added: README.md files are navigational, not
+spec-governed content, and `plugin.json` is JSON, not prose Vale can meaningfully lint.
+
+**Rule categories are prose-pattern-matchable only.** Structural, schema, and security concerns
+stay out of this Vale-based harness because this repo already has dedicated tools for them:
+`skill-frontmatter` (required frontmatter fields), `validate-plugins`/`validate-marketplace`
+(`claude plugin validate --strict`, schema), and `gitleaks`/`detect-private-key` (secrets).
+Duplicating those concerns as Vale rules would fight tools that already own them better.
+
+**Governance docs are excluded as a rule source.** `docs/research/governance_principles/CONTROLS.md`
+and `governance.md` were investigated and found to contribute nothing minable: CONTROLS.md is
+org/CI-infrastructure controls (secret scanning, dependency/license scanning, agent permission
+scoping, audit logging, human approval gates, periodic reviews) — none of it is a prose pattern
+expressible as a Vale rule against SKILL.md/agent-file text, and what it does cover is either
+already handled elsewhere (gitleaks) or genuinely out of scope for a plugin-content prose harness
+(dependency/license scanning is a code-dependency concern, not skill authoring).
+
+**Spec-derived custom rules stay mostly as-is.** Re-reading agentskills.io's
+`optimizing-descriptions.md` and `skill-authoring.md`, plus `claude-code-plugins/agent-definition.md`
+and `github-copilot-plugins/agent-definition.md`, found that the existing four Kyberforge rules
+already cover the pattern-matchable surface those specs describe. The remaining spec guidance —
+calibrating control vs. giving freedom, avoiding menus of options, coherent skill scope, moderate
+detail level — is semantic judgment, already `skill-audit`'s job via LLM review, not new lintable
+rules. One confirmation surfaced: Claude Code's `Use proactively` phrasing is meaningful for `.md`
+agent files (it triggers auto-invocation), unlike Copilot's `.agent.md` files where it's dead
+phrasing — so `KyberforgeCopilot/ProactivePhrase`'s existing `.agent.md`-only scope is correct and
+must not be extended to `.md` files.
+
+**`write-good`/`alex` are trialed, not adopted wholesale.** These built-in/third-party Vale
+packages are tuned for general blog-style prose (passive voice, weasel words, wordy phrases) and
+are expected to be noisy against this repo's terse, imperative instruction-file corpus. Only
+individual rules proven low-noise against the existing corpus get cherry-picked into
+`styles/Kyberforge`; the packages are never referenced wholesale in `BasedOnStyles`.
+
+**A new non-Vale check closes a real gap.** `skill-authoring.md` states `SKILL.md` should stay
+under 500 lines / 5,000 tokens — currently unenforced anywhere in this repo. This is a whole-file
+length ceiling, not a text pattern, so it isn't a Vale rule — it becomes a new deterministic script
+and pre-commit hook, sibling to the existing `skill-frontmatter` hook.
+
+**Rules land directly in `styles/Kyberforge`, enforcing immediately.** No trial/report-only tier
+is introduced (see Considered Options). The implementation pass finalizes the cherry-picked
+`write-good`/`alex` rules and any new spec-derived rule wording, runs the full set against the
+existing SKILL.md/agent-file corpus, fixes any resulting violations across that corpus, and lands
+the rule changes and the corpus fixes as one atomic commit — the same enforcement model as the
+original four rules, never a partial or opt-in state.
+
+## Considered options
+
+**Phased rollout via a separate trial style + config (rejected).** A `styles/KyberforgeTrial/`
+directory plus a parallel `.vale.trial.ini` (mirroring the root config's globs but with
+`BasedOnStyles = Kyberforge, KyberforgeTrial`) would let new rules be swept report-only via
+`lint-runner`/`vale-run` before promotion into the enforcing `styles/Kyberforge` + root
+`.vale.ini`. This was considered because `BasedOnStyles = Kyberforge` activates every rule file
+under that directory automatically — there's no partial/opt-in application within a style, so a
+rule dropped straight into `styles/Kyberforge` goes live in the blocking pre-commit hook
+immediately. Rejected in favor of finalizing rules directly and fixing violations via subagent
+before committing: simpler, no new trial-config machinery to build or maintain — at the cost of no
+standing report-only tier for future candidate rules.
+
+## Consequences
+
+- `styles/Kyberforge/` will gain new rule files once the (separate, later) implementation pass
+  finalizes the exact cherry-picked `write-good`/`alex` rules and any new wording — none are named
+  by this ADR, since none have been chosen yet.
+- A new pre-commit hook (name TBD by the implementer) enforces the 500-line/5,000-token `SKILL.md`
+  ceiling, sibling to `skill-frontmatter`.
+- `styles/KyberforgeTrial/` and `.vale.trial.ini` are deliberately not created — noted here so a
+  future reader doesn't wonder if a trial tier was forgotten.
+- Follow-up work — not part of this ADR — is: syncing and trialing `write-good`/`alex`, cherry-picking
+  low-noise rules, writing the size-ceiling script and hook, fixing existing corpus violations, and
+  the atomic commit landing all of it.