test(agent-presets): assert the derived root through the shipped bundles

The new default's whole claim is that a launcher configuring nothing still
finds a person's presets, and nothing asserted it through a real composition —
`user-root.spec.ts` plugs the service directly, and every other lane pins
`includeUserRoot: false` so the machine's home cannot decide a golden.

This lane boots the real base and web-app bundles with only the shipped root
patched in, points `$DSH_HOME` at a temp home before boot (the derived root is
resolved when the plugin is constructed), and asserts a preset placed there is
listed as `user`, reported healthy, authorable, and mountable into an agent
whose tool catalog it decides.

apps/cli/tests/web-agent-presets.e2e.ts

@@ -634,6 +634,66 @@ describe('a delegated child', () => {
   })
 })
 
+describe('a launcher that configures no writable root', () => {
+  // The claim this default exists for, asserted through the real shipped
+  // bundles rather than a hand-built context: `apps/cli` patches in only the
+  // system root, and a person's own presets are found anyway because the
+  // roster derives `<dshHome>/.agent-presets` itself. `$DSH_HOME` is pointed
+  // at a temp home BEFORE boot — the derived root is resolved when the plugin
+  // is constructed, and an unpinned run would read the developer's own.
+  let derivedCtx: Context
+  let previousHome: string | undefined
+
+  beforeAll(async () => {
+    const home = await mkdtemp(join(tmpdir(), 'dsh-preset-derived-'))
+    previousHome = process.env.DSH_HOME
+    process.env.DSH_HOME = home
+    await mkdir(join(home, '.agent-presets', 'derived-mine'), { recursive: true })
+    await writeFile(
+      join(home, '.agent-presets', 'derived-mine', 'agent.cordis.yml'),
+      '- id: tool-todo\n  name: \'@deepseek-ai/dsh-tool-todo\'\n  config:\n    allowParallelInProgress: true\n',
+    )
+    const settingsFile = join(await mkdtemp(join(tmpdir(), 'dsh-preset-derived-settings-')), 'settings.yaml')
+    await writeFile(settingsFile, '{}\n')
+    // Only the shipped root, exactly what `composeProfile` supplies; the
+    // writable one is the roster's own default rather than this patch's job.
+    derivedCtx = await bootWeb(settingsFile, [{
+      id: 'agent-presets',
+      config: {
+        default: 'standard',
+        roots: [{ path: join(CONFIG_DIR, 'agent-presets'), trust: 'system' }],
+        includeUserRoot: true,
+      },
+    }])
+  }, 120_000)
+
+  afterAll(async () => {
+    if (previousHome === undefined) delete process.env.DSH_HOME
+    else process.env.DSH_HOME = previousHome
+    await derivedCtx.fiber.dispose()
+  })
+
+  it('discovers and mounts a preset the person authored under the harness home', async () => {
+    const listed = await derivedCtx.agentPresets.list()
+
+    const mine = listed.find(preset => preset.id === 'derived-mine')
+    expect(mine).toMatchObject({ trust: 'user' })
+    // Omitted rather than undefined: a healthy row carries no `broken` key.
+    expect(mine?.broken).toBeUndefined()
+    expect(derivedCtx.agentPresets.authorable).toBe(true)
+
+    const handle = await derivedCtx.agents.create({
+      sessionId: SessionId('preset-derived-root'),
+      setup: agentCtx => derivedCtx.agentPresets.mount(agentCtx, 'derived-mine').then(() => undefined),
+    })
+    try {
+      expect(toolNames(derivedCtx, handle.agent)).toContain('todo_write')
+    } finally {
+      await handle.dispose()
+    }
+  })
+})
+
 describe('authoring a preset on the shipped composition', () => {
   let authorCtx: Context
   let userRoot: string