fix(starlark): stop the root display service locking the web UI out

Reported after a fresh install: installing an app from the Starlark tab
failed with "install failed: Failed to install from repository", and so did
uploading a .star file and installing from a GitHub directory. The reporter
found the cause only by reading service logs, and fixed it with

    sudo chown -R ledpi:ledpi /home/ledpi/LEDMatrix/starlark-apps

starlark-apps is gitignored, so it is never checked out -- it is created
lazily by whichever process reaches it first. Those processes run as
different users. systemd/ledmatrix.service is User=root and constructs this
plugin at startup, which is where _get_apps_directory() is called from;
systemd/ledmatrix-web.service runs as the login user and is what actually
installs apps.

The documented first step is to install pixlet and reboot, so on a fresh
machine the display service usually wins that race and mkdir() leaves the
directory root-owned. The web process then fails in _install_star_file() on
app_dir.mkdir(), which catches nothing, so PermissionError reaches the
route's outer `except Exception` and becomes the generic message the user
saw. All three install paths write to the same directory, which is why all
three failed.

The web user cannot repair this -- chown needs root. So root does it, on
every startup, which also heals machines already broken by this without the
owner having to find the chown themselves. It is a no-op when not root, when
the platform has no POSIX ownership, and when the checkout genuinely belongs
to root; a chown that fails warns rather than killing startup.

Also made the failure legible if the handover is ever prevented: a
PermissionError now names the directory, the automatic repair, and the
manual chown, instead of a message that names neither path nor cause.

Verified by mutation: dropping the handover call, chowning a genuinely
root-owned checkout, and letting a non-root process chown each fail their
own test. 121 starlark tests pass.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014RRtqXDCnvnY6EQwhT5CV9

plugin-repos/starlark-apps/manager.py

@@ -457,12 +457,66 @@ class StarlarkAppsPlugin(BasePlugin):
             apps_dir = project_root / "starlark-apps"
         except Exception:
             # Fallback to current working directory
-            apps_dir = Path.cwd() / "starlark-apps"
+            project_root = Path.cwd()
+            apps_dir = project_root / "starlark-apps"
 
         # Create directory if it doesn't exist
         apps_dir.mkdir(parents=True, exist_ok=True)
+        self._hand_apps_dir_to_checkout_owner(apps_dir, project_root)
         return apps_dir
 
+    def _hand_apps_dir_to_checkout_owner(self, apps_dir: Path, project_root: Path) -> None:
+        """Give the apps directory to whoever owns the checkout.
+
+        This directory is not in the repository, so it is created lazily by
+        whichever process reaches it first -- and the two that do run as
+        different users. The display service is `User=root`
+        (systemd/ledmatrix.service) and instantiates this plugin at startup,
+        which is where `_get_apps_directory` is called from. The web interface
+        is `User=<login user>` (systemd/ledmatrix-web.service) and is what
+        actually installs apps.
+
+        On a fresh install the display service usually wins that race -- the
+        documented first step is to install pixlet and reboot -- so the
+        directory lands root-owned, and every subsequent install from the web
+        UI fails on PermissionError. The user sees only "Failed to install
+        from repository", with nothing pointing at ownership.
+
+        The web user cannot repair this; it lacks permission to chown. Root
+        can, so root does it here, on every startup. That also heals installs
+        already broken by this, without the user having to find the chown.
+        """
+        geteuid = getattr(os, "geteuid", None)
+        chown = getattr(os, "chown", None)
+        if geteuid is None or chown is None or geteuid() != 0:
+            # Not root, or not a platform with POSIX ownership. If the
+            # directory is wrong we cannot fix it, and must not pretend to.
+            return
+        try:
+            owner = project_root.stat()
+        except OSError:
+            return
+        if owner.st_uid == 0:
+            # The checkout genuinely belongs to root, so root owning the apps
+            # directory is correct and there is nobody to hand it to.
+            return
+
+        for path in (apps_dir, *apps_dir.rglob("*")):
+            try:
+                st = path.stat()
+            except OSError:
+                continue
+            if st.st_uid == owner.st_uid and st.st_gid == owner.st_gid:
+                continue
+            try:
+                chown(path, owner.st_uid, owner.st_gid)
+            except OSError as e:
+                self.logger.warning(
+                    "Could not hand %s to uid %s: %s -- installs from the web "
+                    "interface will fail until this is chowned manually",
+                    path, owner.st_uid, e,
+                )
+
     def _sanitize_app_id(self, app_id: str) -> str:
         """
         Sanitize app_id into a safe slug for use in file paths.