Skip hidden dirs in the detector walker and vendored paths in scan targets

When impeccable (or any agent tool) is installed into a project's
.claude/.cursor/.codex tree, a root scan descended into the vendored skill
code and reported the detector's own example strings as findings, and
context-signals returned installed-skill files as scan candidates whenever
the harness tree appeared in the branch diff (issue #303).

Rather than growing SKIP_DIRS by a denylist of harness names that drifts
as new tools appear, the walker now skips every hidden directory during
recursion — which already covered .git/.next/.nuxt/.svelte-kit/.turbo/
.vercel, and covers all present and future harness installs plus
.impeccable itself. SKIP_DIRS shrinks to the four non-hidden entries.
An explicitly passed hidden target still scans: only child entries are
name-checked, never the root the walker is given.

scanTargets() applies the same rule to git-changed files (directory
segments only, so root dotfiles keep their existing behavior), and falls
through to source-dir targeting when the only dirty files are vendored.

Prepared with AI assistance (Claude Code), directed by @pbakaus.

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

skill/scripts/context-signals.mjs

@@ -156,9 +156,21 @@ const SCANNABLE_EXT = new Set([
   '.jsx', '.tsx', '.js', '.ts', '.vue', '.svelte', '.astro',
 ]);
 // Where UI source typically lives. The detector walks these and skips
-// node_modules / dist / build / .next / .nuxt automatically.
+// node_modules / dist / build and all hidden dirs automatically.
 const SOURCE_DIRS = ['src', 'app', 'components', 'pages', 'public'];
 
+// A changed file under a hidden or dependency/build directory is not app
+// source — it's a vendored AI-harness install (.claude/skills/..., .cursor/,
+// .impeccable/, issue #303), a build artifact, or a dependency. Mirrors the
+// engine walkDir's skip rule so git-changes targeting can't resurface paths
+// the walker would never visit.
+function isVendoredPath(rel) {
+  const dirSegments = rel.split(/[\\/]/).slice(0, -1);
+  return dirSegments.some(
+    (seg) => seg.startsWith('.') || seg === 'node_modules' || seg === 'dist' || seg === 'build' || seg === '__pycache__',
+  );
+}
+
 /**
  * Local paths the agent should point the bundled detector at — never a URL.
  * A URL means a costly Puppeteer browser render, and a probed dev-server port
@@ -173,6 +185,7 @@ function scanTargets(cwd, git) {
   if (git.isRepo && git.changedFiles.length) {
     const changed = git.changedFiles
       .filter((f) => SCANNABLE_EXT.has(path.extname(f).toLowerCase()))
+      .filter((f) => !isVendoredPath(f))
       .filter((f) => fs.existsSync(path.join(cwd, f)));
     if (changed.length) return { targets: changed.slice(0, 50), via: 'git-changes' };
   }