feat: secure build phase 2 — enforce image verification by default

All store images are now digest-pinned and cosign-signed by the publish
pipeline, so the warn-by-default training-wheels period is over: an
unsigned or undigested image must not install unless the admin
explicitly opts out. The service_composer fallback used when the config
manager is unavailable or corrupt also flips to enforce — config
corruption must fail closed rather than silently weaken verification.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_config_manager.py

@@ -518,7 +518,7 @@ class TestEmailManagerApply(unittest.TestCase):
 
 
 class TestImageVerificationConfig(unittest.TestCase):
-    """image_verification config round-trip and warn-by-default behaviour."""
+    """image_verification config round-trip; default is now 'enforce' (P3)."""
 
     def setUp(self):
         self.temp_dir = tempfile.mkdtemp()
@@ -530,9 +530,9 @@ class TestImageVerificationConfig(unittest.TestCase):
     def tearDown(self):
         shutil.rmtree(self.temp_dir)
 
-    def test_default_mode_is_warn(self):
-        self.assertEqual(self.cm.get_image_verification_mode(), 'warn')
-        self.assertEqual(self.cm.get_image_verification(), {'mode': 'warn'})
+    def test_default_mode_is_enforce(self):
+        self.assertEqual(self.cm.get_image_verification_mode(), 'enforce')
+        self.assertEqual(self.cm.get_image_verification(), {'mode': 'enforce'})
 
     def test_set_and_get_round_trip(self):
         for mode in ('off', 'warn', 'enforce'):
@@ -548,9 +548,9 @@ class TestImageVerificationConfig(unittest.TestCase):
         with self.assertRaises(ValueError):
             self.cm.set_image_verification_mode('paranoid')
 
-    def test_corrupt_section_falls_back_to_warn(self):
+    def test_corrupt_section_falls_back_to_enforce(self):
         self.cm.configs['image_verification'] = {'mode': 'bogus'}
-        self.assertEqual(self.cm.get_image_verification_mode(), 'warn')
+        self.assertEqual(self.cm.get_image_verification_mode(), 'enforce')
 
 
 if __name__ == '__main__':

tests/test_service_composer.py

@@ -874,6 +874,46 @@ class TestImageVerification(unittest.TestCase):
         self.assertTrue(result['ok'])
         c.up.assert_called_once()
 
+    def test_default_mode_is_enforce(self):
+        """get_image_verification_mode default is 'enforce' (P3 flip)."""
+        from config_manager import ConfigManager as RealCM
+        import tempfile, shutil
+        tmpdir = tempfile.mkdtemp()
+        try:
+            cm = RealCM(os.path.join(tmpdir, 'cell_config.json'),
+                        os.path.join(tmpdir, 'data'))
+            c = ServiceComposer(config_manager=cm, data_dir=tmpdir)
+            self.assertEqual(c._verification_mode(), 'enforce')
+        finally:
+            shutil.rmtree(tmpdir)
+
+    def test_enforce_default_rejects_unsigned_image(self):
+        """Under the default enforce mode, an undigested image aborts install."""
+        c = _verify_composer('enforce')
+        c._cosign_verify = MagicMock()
+        manifest = {'image': 'git.pic.ngo/roof/unsigned:latest'}
+        result = c.install('svc', manifest, 'tpl')
+        self.assertFalse(result['ok'])
+        self.assertIn('digest', result['error'])
+        c._cosign_verify.assert_not_called()
+        c.up.assert_not_called()
+
+    def test_mode_read_failure_falls_back_to_enforce(self):
+        """Config corruption must fail closed, not weaken verification."""
+        c = _verify_composer('enforce')
+        c.cm.get_image_verification_mode.side_effect = RuntimeError('corrupt config')
+        self.assertEqual(c._verification_mode(), 'enforce')
+
+    def test_enforce_default_proceeds_with_signed_digested_image(self):
+        """Under the default enforce mode, a digest-pinned signed image proceeds."""
+        c = _verify_composer('enforce')
+        c._cosign_verify = MagicMock(return_value={'ok': True, 'stdout': '[]', 'stderr': ''})
+        manifest = {'image': _SIGNED_IMAGE}
+        result = c.install('svc', manifest, 'tpl')
+        self.assertTrue(result['ok'])
+        c._cosign_verify.assert_called_once()
+        c.up.assert_called_once()
+
 
 if __name__ == '__main__':
     unittest.main()

tests/test_service_store_manager.py

@@ -693,7 +693,7 @@ class TestInstall(unittest.TestCase):
         composer.install.assert_not_called()
 
     def test_install_warn_allows_undigested_image(self):
-        """Under warn mode (default) an undigested image still installs."""
+        """Under warn mode an undigested image still installs (warn is non-default)."""
         manifest = _valid_manifest(
             id='myapp', container_name='cell-myapp',
             image='git.pic.ngo/roof/myapp:latest',
@@ -713,6 +713,19 @@ class TestInstall(unittest.TestCase):
         self.assertTrue(result['ok'])
         composer.install.assert_called_once()
 
+    def test_install_enforce_default_rejects_undigested_image(self):
+        """The new default mode (enforce) rejects undigested images without explicit mode set."""
+        manifest = _valid_manifest(
+            id='myapp', container_name='cell-myapp',
+            image='git.pic.ngo/roof/myapp:latest',
+        )
+        ssm, cm, _, composer = _make_ssm(manifest=manifest)
+        cm.get_image_verification_mode.return_value = 'enforce'
+        result = ssm.install('myapp')
+        self.assertFalse(result['ok'])
+        self.assertIn('digest', result['error'].lower())
+        composer.install.assert_not_called()
+
     def test_install_without_composer_stores_record(self):
         """When service_composer=None, skip compose but still store the install record."""
         manifest = _valid_manifest(id='myapp', container_name='cell-myapp')