diff --git a/test/web_interface/test_starlark_pixlet_routes.py b/test/web_interface/test_starlark_pixlet_routes.py
index f8692f49..82c13ef9 100644
--- a/test/web_interface/test_starlark_pixlet_routes.py
+++ b/test/web_interface/test_starlark_pixlet_routes.py
@@ -15,6 +15,7 @@
 """
 
 import json
+import os
 from unittest.mock import MagicMock, patch
 
 import pytest
@@ -305,4 +306,90 @@ def test_a_traversal_app_id_is_rejected_before_touching_the_manifest(self, clien
         resp = client.post('/api/v3/plugins/toggle',
                            json={'plugin_id': 'starlark:../../etc/passwd', 'enabled': True})
         assert resp.status_code == 400
-        assert 'invalid characters' in resp.get_json()['message']
+        assert 'traversal' in resp.get_json()['message']
+
+    def test_an_app_id_the_listing_published_can_be_toggled(self, client):
+        """The id here is exactly what _starlark_virtual_plugins publishes.
+
+        It used to be re-slugified on the way back in -- lowercased, with every
+        character outside [a-z0-9_] replaced -- so an app stored as 'My-App'
+        was listed as 'starlark:My-App' and looked up as 'my_app'. Toggling an
+        app the page had just drawn answered 404.
+        """
+        manifest = {'apps': {'My-App': {'name': 'My App', 'enabled': False}}}
+        with patch('web_interface.blueprints.api_v3._get_starlark_plugin', return_value=None), \
+             patch('web_interface.blueprints.api_v3._read_starlark_manifest',
+                   return_value=manifest), \
+             patch('web_interface.blueprints.api_v3._write_starlark_manifest',
+                   return_value=True) as write:
+            resp = client.post('/api/v3/plugins/toggle',
+                               json={'plugin_id': 'starlark:My-App', 'enabled': True})
+        assert resp.status_code == 200, resp.get_json()
+        assert write.called, "the toggle never reached the manifest"
+        assert manifest['apps']['My-App']['enabled'] is True
+
+    def test_a_loaded_app_missing_from_the_manifest_does_not_500(self, client):
+        """_update_manifest_safe does not catch KeyError, so indexing an entry
+        that is not on disk yet escaped as a 500 instead of writing it."""
+        app = MagicMock()
+        app.manifest = {'enabled': False}
+        plugin = MagicMock()
+        plugin.apps = {'demo': app}
+        written = {}
+
+        def run_updater(fn):
+            fn(written)
+            return True
+
+        plugin._update_manifest_safe.side_effect = run_updater
+
+        with patch('web_interface.blueprints.api_v3._get_starlark_plugin', return_value=plugin):
+            resp = client.post('/api/v3/plugins/toggle',
+                               json={'plugin_id': 'starlark:demo', 'enabled': True})
+        assert resp.status_code == 200, resp.get_json()
+        assert written['apps']['demo']['enabled'] is True
+
+
+class TestTheManifestStaysRelocatable:
+    """`star_file` is joined to the app's own directory by its readers.
+
+    _standalone_render_starlark_app does `app_dir / app_data.get('star_file',
+    f'{app_id}.star')`, so the key's default is a bare filename. Storing an
+    absolute path gave it a second meaning, and Path.__truediv__ discards the
+    left side when the right is absolute -- which pinned the manifest to the
+    PROJECT_ROOT that installed it.
+    """
+
+    @pytest.fixture
+    def starlark_dir(self, tmp_path, monkeypatch):
+        from web_interface.blueprints import api_v3 as module
+        apps_dir = tmp_path / "starlark-apps"
+        apps_dir.mkdir()
+        monkeypatch.setattr(module, '_STARLARK_APPS_DIR', apps_dir)
+        monkeypatch.setattr(module, '_STARLARK_MANIFEST_FILE', apps_dir / 'manifest.json')
+        return apps_dir
+
+    def _install(self, tmp_path):
+        from web_interface.blueprints import api_v3 as module
+        source = tmp_path / "source.star"
+        source.write_text("# app")
+        with patch.object(module, '_get_pixlet_renderer_class',
+                          side_effect=ImportError("no pixlet here")):
+            assert module._install_star_file('demo', str(source), {'name': 'Demo'})
+        return json.loads((module._STARLARK_MANIFEST_FILE).read_text())['apps']['demo']
+
+    def test_the_star_file_is_recorded_by_name(self, starlark_dir, tmp_path):
+        assert self._install(tmp_path)['star_file'] == 'demo.star'
+
+    def test_the_recorded_path_is_not_absolute(self, starlark_dir, tmp_path):
+        """An absolute value survives a move only by accident."""
+        assert not os.path.isabs(self._install(tmp_path)['star_file'])
+
+    def test_the_value_resolves_against_the_app_directory(self, starlark_dir, tmp_path):
+        """Which is the one thing every reader of this key does with it."""
+        entry = self._install(tmp_path)
+        assert (starlark_dir / 'demo' / entry['star_file']).is_file()
+
+    def test_it_matches_the_default_a_reader_falls_back_to(self, starlark_dir, tmp_path):
+        """Stored and defaulted values must mean the same thing."""
+        assert self._install(tmp_path)['star_file'] == 'demo.star'
diff --git a/web_interface/blueprints/api_v3.py b/web_interface/blueprints/api_v3.py
index 377244d5..1ef82673 100644
--- a/web_interface/blueprints/api_v3.py
+++ b/web_interface/blueprints/api_v3.py
@@ -9144,7 +9144,13 @@ def _install_star_file(app_id: str, star_file_path: str, metadata: Dict[str, Any
         'render_interval': metadata.get('render_interval', 300),
         'display_duration': metadata.get('display_duration', 15),
         'config': metadata.get('config', {}),
-        'star_file': str(dest),
+        # The filename, not the full path. Readers join this to the app's own
+        # directory and fall back to a bare '<app_id>.star', so an absolute
+        # value gave the key two meanings -- and Path.__truediv__ discards the
+        # left side when the right is absolute, which pinned the manifest to
+        # whatever PROJECT_ROOT installed it. Moving or redeploying the install
+        # then left the app unable to find its own file.
+        'star_file': dest.name,
     }
     return _write_starlark_manifest(manifest)
 
@@ -9796,14 +9802,28 @@ def _starlark_virtual_plugins() -> list:
 
 def _toggle_starlark_app(app_id: str, enabled: bool):
     """Enable or disable one Starlark app, loaded or not."""
-    safe_id, err = _validate_and_sanitize_app_id(app_id)
+    # Check for traversal, but toggle the key that was listed.
+    # _starlark_virtual_plugins publishes the raw manifest key, while
+    # _validate_and_sanitize_app_id lowercases it and rewrites every character
+    # outside [a-z0-9_]: an app stored as 'My-App' was offered to the UI as
+    # 'starlark:My-App' and looked up here as 'my_app', so toggling an app the
+    # page had just drawn answered 404. Keys written by _install_star_file are
+    # already sanitised; ones written by the plugin, or edited by hand, are
+    # not. _validate_starlark_app_path rejects traversal without rewriting.
+    _, err = _validate_starlark_app_path(app_id)
     if err:
-        return jsonify({'status': 'error', 'message': f'Invalid app_id: {err}'}), 400
+        # err already names app_id; do not prefix it a second time.
+        return jsonify({'status': 'error', 'message': err}), 400
+    safe_id = app_id
 
     plugin = _get_starlark_plugin()
     if plugin is not None and safe_id in getattr(plugin, 'apps', {}):
         def _update(manifest):
-            manifest['apps'][safe_id]['enabled'] = enabled
+            # setdefault rather than indexing: the app is loaded, but its
+            # on-disk entry need not exist, and _update_manifest_safe does not
+            # catch KeyError -- it would escape as a 500 rather than the error
+            # this returns.
+            manifest.setdefault('apps', {}).setdefault(safe_id, {})['enabled'] = enabled
 
         if plugin._update_manifest_safe(_update) is False:
             return jsonify({'status': 'error',