test: add prefix config tests + README switching instructions

8 structural tests for persistent prefix setting:
config reading, --prefix flag, config persistence, interactive
prompt, TTY fallback, reverse cleanup, cleanup ordering, welcome.

README.md

@@ -259,6 +259,10 @@ Data is stored in [Supabase](https://supabase.com) (open source Firebase alterna
 
 **Stale install?** Run `/gstack-upgrade` — or set `auto_upgrade: true` in `~/.gstack/config.yaml`
 
+**Want shorter commands?** `cd ~/.claude/skills/gstack && ./setup --no-prefix` — switches from `/gstack-qa` to `/qa`. Your choice is remembered for future upgrades.
+
+**Want namespaced commands?** `cd ~/.claude/skills/gstack && ./setup --prefix` — switches from `/qa` to `/gstack-qa`. Useful if you run other skill packs alongside gstack.
+
 **Codex says "Skipped loading skill(s) due to invalid SKILL.md"?** Your Codex skill descriptions are stale. Fix: `cd ~/.codex/skills/gstack && git pull && ./setup --host codex` — or for repo-local installs: `cd "$(readlink -f .agents/skills/gstack)" && git pull && ./setup --host codex`
 
 **Windows users:** gstack works on Windows 11 via Git Bash or WSL. Node.js is required in addition to Bun — Bun has a known bug with Playwright's pipe transport on Windows ([bun#4253](https://github.com/oven-sh/bun/issues/4253)). The browse server automatically falls back to Node.js. Make sure both `bun` and `node` are on your PATH.

test/gen-skill-docs.test.ts

@@ -1685,6 +1685,56 @@ describe('setup script validation', () => {
     );
     expect(claudeInstallSection).toContain('cleanup_old_claude_symlinks');
   });
+
+  // --- Persistent config + interactive prompt tests ---
+
+  test('setup reads skill_prefix from config', () => {
+    expect(setupContent).toContain('get skill_prefix');
+    expect(setupContent).toContain('GSTACK_CONFIG');
+  });
+
+  test('setup supports --prefix flag', () => {
+    expect(setupContent).toContain('--prefix)');
+    expect(setupContent).toContain('SKILL_PREFIX=1; SKILL_PREFIX_FLAG=1');
+  });
+
+  test('--prefix and --no-prefix persist to config', () => {
+    expect(setupContent).toContain('set skill_prefix');
+  });
+
+  test('interactive prompt shows when no config', () => {
+    expect(setupContent).toContain('Short names');
+    expect(setupContent).toContain('Namespaced');
+    expect(setupContent).toContain('Choice [1/2]');
+  });
+
+  test('non-TTY defaults to flat names', () => {
+    // Should check if stdin is a TTY before prompting
+    expect(setupContent).toContain('-t 0');
+  });
+
+  test('cleanup_prefixed_claude_symlinks exists and uses readlink', () => {
+    expect(setupContent).toContain('cleanup_prefixed_claude_symlinks');
+    const fnStart = setupContent.indexOf('cleanup_prefixed_claude_symlinks()');
+    const fnEnd = setupContent.indexOf('}', setupContent.indexOf('removed[@]}', fnStart));
+    const fnBody = setupContent.slice(fnStart, fnEnd);
+    expect(fnBody).toContain('readlink');
+    expect(fnBody).toContain('gstack-$skill_name');
+  });
+
+  test('reverse cleanup runs before link when prefix is disabled', () => {
+    const claudeInstallSection = setupContent.slice(
+      setupContent.indexOf('INSTALL_CLAUDE'),
+      setupContent.lastIndexOf('link_claude_skill_dirs')
+    );
+    expect(claudeInstallSection).toContain('cleanup_prefixed_claude_symlinks');
+  });
+
+  test('welcome message references SKILL_PREFIX', () => {
+    // gstack-upgrade is always called gstack-upgrade (it's the actual dir name)
+    // but the welcome section should exist near the prefix logic
+    expect(setupContent).toContain('Run /gstack-upgrade anytime');
+  });
 });
 
 describe('discover-skills hidden directory filtering', () => {