feat(setup): install sections/ for cherry-pick targets (claude + kiro) (T9)

Two install targets cherry-pick SKILL.md and would leave a carved skill's
sections/ behind, 404ing a runtime 'Read sections/<name>.md':
- link_claude_skill_dirs: link the sections/ subdir via _link_or_copy (windows
  gets a fresh copy on every ./setup)
- kiro per-skill loop: sed-rewrite + copy each sections/* so paths resolve under
  ~/.kiro, not ~/.codex/~/.claude

codex/factory/opencode link the whole generated dir, so sections ride free.
Addresses Codex outside-voice #4/#6 (runtime pathing landmine). Inert until a
skill is carved. Static-tripwire test + windows-fallback invariant green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/setup-sections-linking.test.ts

@@ -0,0 +1,48 @@
+/**
+ * Static invariant: the two install targets that cherry-pick SKILL.md (Claude
+ * prefixed dirs + Kiro) must ALSO install the sections/ subdir, or a carved
+ * skill's runtime "Read sections/<name>.md" 404s. codex/factory/opencode link
+ * the whole generated dir, so sections ride along for free there.
+ *
+ * Matches the repo's static-tripwire style (setup-windows-fallback,
+ * cdp-session-cleanup). End-to-end "sections resolve in a temp install" runs in
+ * the group-5/6 functional pass once real ship/sections/ exist.
+ */
+
+import { describe, test, expect } from 'bun:test';
+import * as fs from 'fs';
+import * as path from 'path';
+
+const SETUP = fs.readFileSync(path.join(import.meta.dir, '..', 'setup'), 'utf-8');
+
+/** Body of a shell function `name() { ... }` up to the closing line `}`. */
+function fnBody(src: string, name: string): string {
+  const start = src.indexOf(`${name}() {`);
+  if (start === -1) return '';
+  const end = src.indexOf('\n}', start);
+  return src.slice(start, end === -1 ? undefined : end);
+}
+
+describe('setup links sections/ for cherry-pick install targets', () => {
+  test('link_claude_skill_dirs links sections/ via _link_or_copy', () => {
+    const body = fnBody(SETUP, 'link_claude_skill_dirs');
+    expect(body).toContain('sections');
+    // sections install must route through the windows-safe helper, not raw ln.
+    expect(body).toMatch(/_link_or_copy\s+"\$gstack_dir\/\$dir_name\/sections"\s+"\$target\/sections"/);
+    expect(body).toMatch(/if \[ -d "\$gstack_dir\/\$dir_name\/sections" \]/);
+  });
+
+  test('kiro per-skill loop rewrites + copies sections/*', () => {
+    // Kiro builds from the codex output and sed-rewrites paths; sections must get
+    // the same rewrite so they resolve under ~/.kiro, not ~/.codex or ~/.claude.
+    expect(SETUP).toMatch(/if \[ -d "\$skill_dir\/sections" \]/);
+    expect(SETUP).toMatch(/mkdir -p "\$target_dir\/sections"/);
+    expect(SETUP).toContain('$target_dir/sections/$(basename "$section_file")');
+  });
+
+  test('no raw ln introduced (windows-fallback invariant still holds)', () => {
+    // Every new line touching sections uses _link_or_copy or sed redirect, never ln.
+    const sectionLines = SETUP.split('\n').filter(l => l.includes('sections') && /\bln\s+-/.test(l));
+    expect(sectionLines).toEqual([]);
+  });
+});