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>

setup

@@ -474,6 +474,14 @@ link_claude_skill_dirs() {
       # Validate target isn't a symlink before creating the link
       if [ -L "$target/SKILL.md" ]; then rm "$target/SKILL.md"; fi
       _link_or_copy "$gstack_dir/$dir_name/SKILL.md" "$target/SKILL.md"
+      # Link the sections/ subdir for carved skills (v2 plan T9). The prefixed
+      # Claude skill dir otherwise holds only SKILL.md, so a runtime
+      # "Read sections/<name>.md" 404s. Route through _link_or_copy so Windows
+      # gets a fresh copy (and re-copies on every ./setup, refreshing staleness).
+      if [ -d "$gstack_dir/$dir_name/sections" ]; then
+        if [ -e "$target/sections" ] || [ -L "$target/sections" ]; then rm -rf "$target/sections"; fi
+        _link_or_copy "$gstack_dir/$dir_name/sections" "$target/sections"
+      fi
       linked+=("$link_name")
     fi
   done
@@ -1049,6 +1057,20 @@ if [ "$INSTALL_KIRO" -eq 1 ]; then
           -e "s|~/.codex/skills/gstack|~/.kiro/skills/gstack|g" \
           -e "s|~/.claude/skills/gstack|~/.kiro/skills/gstack|g" \
           "$skill_dir/SKILL.md" > "$target_dir/SKILL.md"
+      # Carved skills (v2 plan T9): rewrite + copy each sections/*.md the same way,
+      # so a runtime "Read sections/<name>.md" resolves under ~/.kiro and doesn't
+      # leak a ~/.codex or ~/.claude path. Kiro builds from the codex output, so
+      # these section files only exist for skills that have been carved.
+      if [ -d "$skill_dir/sections" ]; then
+        mkdir -p "$target_dir/sections"
+        for section_file in "$skill_dir/sections"/*; do
+          [ -f "$section_file" ] || continue
+          sed -e 's|\$HOME/.codex/skills/gstack|$HOME/.kiro/skills/gstack|g' \
+              -e "s|~/.codex/skills/gstack|~/.kiro/skills/gstack|g" \
+              -e "s|~/.claude/skills/gstack|~/.kiro/skills/gstack|g" \
+              "$section_file" > "$target_dir/sections/$(basename "$section_file")"
+        done
+      fi
     done
     echo "gstack ready (kiro)."
     echo "  browse: $BROWSE_BIN"

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([]);
+  });
+});