fix(rbac): block preview public channels

supabase/functions/_backend/public/channel/post.ts

@@ -342,8 +342,15 @@ export async function post(c: Context<MiddlewareKeyVariables>, body: ChannelSet,
       throw simpleError('cannot_access_app', 'You can\'t access this app', { app_id: body.app_id, channel: body.channel })
     }
   }
-  else if (!(await checkPermission(c, 'app.create_channel', { appId: body.app_id }))) {
-    throw simpleError('cannot_access_app', 'You can\'t access this app', { app_id: body.app_id })
+  else {
+    if (!(await checkPermission(c, 'app.create_channel', { appId: body.app_id }))) {
+      throw simpleError('cannot_access_app', 'You can\'t access this app', { app_id: body.app_id })
+    }
+    // A public/default channel changes the app's delivery configuration. Preview
+    // keys may bootstrap private channels only, so they cannot make one public.
+    if (body.public === true && !(await checkPermission(c, 'app.update_settings', { appId: body.app_id }))) {
+      throw simpleError('cannot_access_app', 'You can\'t access this app', { app_id: body.app_id, channel: body.channel })
+    }
   }
   const { data: org, error } = await supabaseAdmin(c).from('apps').select('owner_org').eq('app_id', body.app_id).single()
   if (error || !org) {

supabase/migrations/20260717133500_app_preview_public_channel_guard.sql

@@ -0,0 +1,36 @@
+-- A public/default channel changes app delivery settings. App-preview keys may
+-- bootstrap private channels, but must not make a newly created channel public.
+-- Keep this in INSERT RLS because `channel add --default` writes the table
+-- directly; the channel endpoint performs the matching guard for its raw SQL
+-- create-and-promote transaction.
+DROP POLICY IF EXISTS "Allow RBAC channels insert" ON public.channels;
+CREATE POLICY "Allow RBAC channels insert"
+ON public.channels
+FOR INSERT
+TO anon, authenticated
+WITH CHECK (
+  public.rbac_check_permission_request(
+    public.rbac_perm_app_create_channel(),
+    owner_org,
+    app_id,
+    NULL::bigint
+  )
+  AND (
+    "public" IS FALSE
+    OR public.rbac_check_permission_request(
+      public.rbac_perm_app_update_settings(),
+      owner_org,
+      app_id,
+      NULL::bigint
+    )
+  )
+  AND (
+    (version IS NULL AND rollout_version IS NULL)
+    OR public.rbac_check_permission_request(
+      public.rbac_perm_channel_promote_bundle(),
+      owner_org,
+      app_id,
+      NULL::bigint
+    )
+  )
+);

tests/channel-post.unit.test.ts

@@ -256,6 +256,26 @@ describe('public channel post', () => {
     expect(updateOrCreateChannel).toHaveBeenCalledWith(c, expect.not.objectContaining({ electron: false }), null, true)
   })
 
+  it('requires app settings permission to create a public channel', async () => {
+    checkPermission
+      .mockResolvedValueOnce(true)
+      .mockResolvedValueOnce(false)
+    const { post } = await import('../supabase/functions/_backend/public/channel/post.ts')
+    const c = context()
+
+    await expect(post(c, {
+      app_id: 'com.test.preview',
+      channel: 'preview-default',
+      public: true,
+    }, apiKey())).rejects.toMatchObject({
+      cause: expect.objectContaining({ error: 'cannot_access_app' }),
+    })
+
+    expect(checkPermission).toHaveBeenNthCalledWith(1, c, 'app.create_channel', { appId: 'com.test.preview' })
+    expect(checkPermission).toHaveBeenNthCalledWith(2, c, 'app.update_settings', { appId: 'com.test.preview' })
+    expect(updateOrCreateChannel).not.toHaveBeenCalled()
+  })
+
   it('preserves the stable version for a settings-only update without channel.read or bundle lookup', async () => {
     const fromCalls: string[] = []
     supabaseAdmin.mockImplementation(() => buildAdminChain({

tests/cli-preview-lifecycle.test.ts

@@ -76,6 +76,8 @@ const APPNAME = `com.cli.preview.lifecycle.${id}`
 const CHANNEL_NAME = `preview-${id.slice(0, 8)}`
 const SECOND_CHANNEL_NAME = `preview-other-${id.slice(0, 8)}`
 const MAIN_CHANNEL_NAME = `main-${id.slice(0, 8)}`
+const DEFAULT_CHANNEL_NAME = `preview-default-${id.slice(0, 8)}`
+const PUBLIC_POST_CHANNEL_NAME = `preview-public-post-${id.slice(0, 8)}`
 const BUNDLE_NAME = `1.0.0-preview-${id.slice(0, 8)}`
 const LEGACY_CHANNEL_NAME = `preview-legacy-${id.slice(0, 8)}`
 const LEGACY_BUNDLE_NAME = `1.0.0-legacy-${id.slice(0, 8)}`
@@ -248,6 +250,34 @@ describe('cli app preview lifecycle', () => {
       supaAnon: SUPABASE_ANON_KEY,
     }
 
+    await expect(addChannelInternal(DEFAULT_CHANNEL_NAME, APPNAME, {
+      ...cliOptions,
+      default: true,
+    }, true)).rejects.toThrow('Cannot create channel')
+
+    const publicChannelResponse = await fetch(`${BASE_URL}/channel`, {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        'capgkey': apiKey.key,
+      },
+      body: JSON.stringify({
+        app_id: APPNAME,
+        channel: PUBLIC_POST_CHANNEL_NAME,
+        public: true,
+      }),
+    })
+    expect(publicChannelResponse.status).toBe(400)
+    await expect(publicChannelResponse.json()).resolves.toMatchObject({ error: 'cannot_access_app' })
+
+    const blockedPublicChannels = await executeSQL(
+      `SELECT COUNT(*)::integer AS count
+       FROM public.channels
+       WHERE app_id = $1 AND name = ANY($2::varchar[])`,
+      [APPNAME, [DEFAULT_CHANNEL_NAME, PUBLIC_POST_CHANNEL_NAME]],
+    )
+    expect(Number(blockedPublicChannels[0]?.count ?? 0)).toBe(0)
+
     const { upload, requests } = await (async () => {
       const fetchSpy = vi.spyOn(globalThis, 'fetch')
       try {