fix(ultraplan-local): v2.3.2 — skill-drafter slug-collision hint

skill-drafter now reads {catalog_root}/<slug>.md before writing its
draft and prepends a warning block to its confirmation output when
an existing skill would be overwritten during manual `mv` promotion.
The draft is still written to .drafts/<slug>.md — the check is a
hint, not a block.

Closes v2.3.0 dogfood finding (post_dogfood_findings[0]): the
drafter produced .drafts/hooks-pattern.md when an approved
hooks-pattern.md seed already existed, giving no signal that `mv`
during promotion would silently overwrite the seed. v2.3.1
introduced the qualified-slug mechanism to resolve such collisions;
v2.3.2 surfaces them at the right moment — before promotion.

Changes:
- agents/skill-drafter.md — new Step 2 between slug computation and
  source reading. Reads {catalog_root}/<slug>.md, inspects
  review_status, derives a kebab-case qualifier from the concept
  handle (or source basename fallback). Subsequent steps renumbered
  3→7. Output format gains Collision: field and optional warning
  block. New Hard Rule.
- tests/fixtures/skill-drafter/slug-collision-expected.md — reference
  fixture documenting expected confirmation shape across four
  scenarios (no collision, approved collision, soft pending
  collision, collision with no good qualifier). Skill-drafter is
  prompt-driven; fixture anchors shape for human verification and
  downstream parsers.
- CHANGELOG [2.3.2], plugin.json 2.3.1→2.3.2, README badge, plugin
  CLAUDE.md slug-convention Collision-hint bullet, marketplace root
  README summary, marketplace root CLAUDE.md plugin table.

Non-breaking. No frontmatter/drafts-layout/tool-scope/regex changes.
Existing pipelines see one extra field and an optional warning —
both purely additive.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

plugins/ultraplan-local/agents/skill-drafter.md

@@ -54,13 +54,48 @@ message — do not write a file with an invalid name.
 
 The draft file path is `{catalog_root}/.drafts/<slug>.md`.
 
-### 2. Read the source
+### 2. Check for slug collision at the catalog root
+
+Before proceeding, attempt to `Read` `{catalog_root}/<slug>.md` (the
+approved location, NOT the draft location).
+
+- If the read fails because the file does not exist → no collision.
+  Proceed to Step 3. Record `collision: false` for the summary.
+- If the read succeeds → inspect the frontmatter for `review_status`.
+  - `review_status: approved` → **collision**. Record it and derive a
+    suggested qualified slug (see "Suggesting a qualifier" below).
+  - `review_status: pending` or `auto-merged` → **soft collision**.
+    Still record and surface it, but the existing file is not a
+    guaranteed baseline; the human reviewer can decide.
+  - Missing or malformed frontmatter → treat as soft collision. Note
+    it in the summary so the reviewer can inspect.
+
+**Do not block** on any of these outcomes. The draft is still
+written to `.drafts/<slug>.md` in Step 7. The collision check exists
+to surface the overwrite risk in your confirmation output so the
+user sees it before running `mv` during manual promotion.
+
+**Suggesting a qualifier.** Pick a short, descriptive kebab-case
+word from the `concept` field (3–6 word handle from
+`concept-extractor`). Strip stopwords like "the", "a", "and". Prefer
+the most specific noun or named pattern in the handle. If the
+concept is generic and no good qualifier emerges, fall back to the
+source basename (e.g., `docs/hooks-recipes.md` → `recipes`).
+
+The suggested qualified slug is
+`<cc_feature>-<qualifier>-<layer>.md`. Validate it against the
+filename regex just like Step 1. If the suggestion collides with
+another existing skill (approved or pending), try the next candidate
+qualifier from the concept handle. If no candidate is collision-free,
+report `suggested_slug: none — reviewer must pick`.
+
+### 3. Read the source
 
 Read the source file in full. Extract the load-bearing ideas that map
 to the concept handle. You are not summarizing the source verbatim —
 you are reframing it as catalog skill content.
 
-### 3. Compose the frontmatter
+### 4. Compose the frontmatter
 
 The frontmatter MUST have exactly these 9 fields, in this order, with
 exactly these values:
@@ -85,7 +120,7 @@ not 0). `review_status` MUST be `pending` (not `approved`, not
 populates `ngram_overlap_score`; the human reviewer in promotion
 flips `review_status`.
 
-### 4. Compose the body
+### 5. Compose the body
 
 The body is 150 to 600 words. Use progressive disclosure: short
 headings, bullet notes, no long prose paragraphs. Imperative voice,
@@ -115,7 +150,7 @@ For `layer: pattern`, structure as:
 Each section gets 2–4 short bullets or one short paragraph. Skip
 sections that have no content rather than padding them.
 
-### 5. Rephrase — do not copy
+### 6. Rephrase — do not copy
 
 You MUST NOT copy verbatim phrases from the source. Rephrase every
 sentence in your own words. The downstream `ip-hygiene-checker` runs
@@ -130,7 +165,7 @@ a fixed YAML schema), do not draft it. Stop and emit a short
 escalate. Better to skip than to ship a draft that will fail
 hygiene.
 
-### 6. Write the file
+### 7. Write the file
 
 Use the `Write` tool to create the draft at
 `{catalog_root}/.drafts/<slug>.md`. Overwrite if it exists — the
@@ -147,9 +182,30 @@ After writing the file, return a short confirmation:
 Drafted: <full path to .drafts/<slug>.md>
 Word count: <body word count>
 Frontmatter: 9 fields, review_status=pending, ngram_overlap_score=null
+Collision: <none | approved | pending | auto-merged | soft>
 Next: ip-hygiene-checker for IP scoring
 ```
 
+If Step 2 detected a collision at `{catalog_root}/<slug>.md`, prepend
+a warning block to the confirmation:
+
+```
+⚠️  Slug collision at catalog root
+   Existing: {catalog_root}/<slug>.md (review_status=<status>)
+   Draft:    {catalog_root}/.drafts/<slug>.md (this run)
+   Risk:     manual `mv` during promotion will silently overwrite the existing file.
+   Suggested qualified slug: <cc_feature>-<qualifier>-<layer>.md
+   Reason for qualifier:     <one short sentence citing the concept handle>
+   Action:                   rename the draft before `mv`, or revise the existing baseline.
+```
+
+If no collision-free qualifier could be derived, replace the
+"Suggested qualified slug" line with:
+
+```
+   Suggested qualified slug: none — reviewer must pick one manually.
+```
+
 If you stopped because of `too-technical-to-paraphrase`, return:
 
 ```
@@ -180,6 +236,11 @@ No file written.
   copied draft is wasted work.
 - **`.drafts/` only.** Never write to the catalog root. Promotion is
   manual `mv` by the user (fase-1 boundary).
+- **Slug-collision pre-write check.** Always `Read`
+  `{catalog_root}/<slug>.md` before writing the draft. If the file
+  exists, surface the collision in the confirmation output with a
+  suggested qualified slug. Never block the draft write — the warning
+  exists so the user sees the overwrite risk before running `mv`.
 - **Privacy.** Strip any secret-looking strings from the source
   before drafting; if the source is meaningfully about credentials,
   abort with `too-technical-to-paraphrase`.