fix(web): stop reporting "no update" when the update check could not run

check-update returned update_available=False whenever git failed. The banner
is the only route to the update button, so a checkout git refuses to touch
looked exactly like a current one -- permanently, with nothing on screen to
act on and only a log line recording why.

The common cause is an install performed as root. scripts/install/one-shot-install.sh
clones into ${HOME}/LEDMatrix, never consults SUDO_USER, and contains no chown
at all, while its own error text suggests running the whole thing under sudo.
The result is a root-owned checkout, and on a rig this is what every git
command in it does:

    fatal: detected dubious ownership in repository at '...'

including the fetch this endpoint runs. Verified on real hardware rather than
assumed.

A failed check now reports check_failed with a message the user can act on --
for dubious ownership, the chown that fixes it. The banner shows that message
instead of hiding itself, with the update button suppressed since updating
cannot work until the cause is fixed. The success path is untouched.

This does not fix the installer, which is the real cause; it stops the symptom
being invisible. The installer needs SUDO_USER handling and a chown, and its
suggestion to run as root should go.

Reverting the endpoint change fails four of the five new tests; the fifth
guards the success path and correctly does not move.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01STMbQE4YctTacQXfbYqKuW

src/common/scroll_helper.py

@@ -328,7 +328,7 @@ class ScrollHelper:
             elapsed_time = current_time - (self.scroll_start_time or current_time)
             # The image already includes display_width padding, so we only need total_scroll_width
             required_total_distance = self.total_scroll_width
-            self.logger.debug(
+            self.logger.info(
                 "Scroll progress: elapsed=%.2fs, target=%.2fs, total_scrolled=%.0f/%d px (%.1f%%)",
                 elapsed_time,
                 self.calculated_duration,

src/vegas_mode/plugin_adapter.py

@@ -83,7 +83,7 @@ class PluginAdapter:
         # into unrelated headlines once the strip refreshed to 9,505px.
         self._offset_shapes: dict = {}
 
-        logger.debug(
+        logger.info(
             "PluginAdapter initialized: display=%dx%d",
             self.display_width, self.display_height
         )
@@ -109,7 +109,7 @@ class PluginAdapter:
         Returns:
             List of PIL Images representing plugin content, or None if no content
         """
-        logger.debug(
+        logger.info(
             "[%s] Getting content (class=%s)",
             plugin_id, plugin.__class__.__name__
         )
@@ -118,7 +118,7 @@ class PluginAdapter:
         cached = self._get_cached(plugin_id)
         if cached is not None:
             total_width = sum(img.width for img in cached)
-            logger.debug(
+            logger.info(
                 "[%s] Using cached content: %d images, %dpx total",
                 plugin_id, len(cached), total_width
             )
@@ -126,46 +126,46 @@ class PluginAdapter:
 
         # Try native Vegas content method first
         has_native = hasattr(plugin, 'get_vegas_content')
-        logger.debug("[%s] Has get_vegas_content: %s", plugin_id, has_native)
+        logger.info("[%s] Has get_vegas_content: %s", plugin_id, has_native)
         if has_native:
             content = self._get_native_content(plugin, plugin_id, offscreen_only)
             if content:
                 total_width = sum(img.width for img in content)
-                logger.debug(
+                logger.info(
                     "[%s] Native content SUCCESS: %d images, %dpx total",
                     plugin_id, len(content), total_width
                 )
                 return self._finalize(content, plugin_id, 'native', plugin)
-            logger.debug("[%s] Native content returned None", plugin_id)
+            logger.info("[%s] Native content returned None", plugin_id)
 
         # Try to get scroll_helper's cached image (for scrolling plugins like stocks/odds)
         has_scroll_helper = hasattr(plugin, 'scroll_helper')
-        logger.debug("[%s] Has scroll_helper: %s", plugin_id, has_scroll_helper)
+        logger.info("[%s] Has scroll_helper: %s", plugin_id, has_scroll_helper)
         content = self._get_scroll_helper_content(plugin, plugin_id, offscreen_only)
         if content:
             total_width = sum(img.width for img in content)
-            logger.debug(
+            logger.info(
                 "[%s] ScrollHelper content SUCCESS: %d images, %dpx total",
                 plugin_id, len(content), total_width
             )
             return self._finalize(content, plugin_id, 'scroll_helper', plugin)
         if has_scroll_helper:
-            logger.debug("[%s] ScrollHelper content returned None", plugin_id)
+            logger.info("[%s] ScrollHelper content returned None", plugin_id)
 
         if offscreen_only:
             # Display capture needs the shared canvas; leave it to the caller.
-            logger.debug(
+            logger.info(
                 "[%s] Needs display capture, deferring to the render thread",
                 plugin_id
             )
             return None
 
         # Fall back to display capture
-        logger.debug("[%s] Trying fallback display capture...", plugin_id)
+        logger.info("[%s] Trying fallback display capture...", plugin_id)
         content = self._capture_display_content(plugin, plugin_id)
         if content:
             total_width = sum(img.width for img in content)
-            logger.debug(
+            logger.info(
                 "[%s] Fallback capture SUCCESS: %d images, %dpx total",
                 plugin_id, len(content), total_width
             )
@@ -226,7 +226,7 @@ class PluginAdapter:
             kept.append(result.image)
 
         if not kept:
-            logger.debug(
+            logger.info(
                 "[%s] All %d image(s) from %s were blank — contributing nothing",
                 plugin_id, len(images), source
             )
@@ -235,14 +235,14 @@ class PluginAdapter:
         trimmed_width = sum(img.width for img in kept)
 
         if trimmed_width < self.config.min_plugin_width:
-            logger.debug(
+            logger.info(
                 "[%s] Trimmed content %dpx is below min_plugin_width %dpx — skipping",
                 plugin_id, trimmed_width, self.config.min_plugin_width
             )
             return None
 
         if trimmed_width != original_width or dropped_blank:
-            logger.debug(
+            logger.info(
                 "[%s] Trimmed %s content: %dpx -> %dpx (%.0f%% reclaimed), "
                 "%d image(s) kept, %d blank dropped",
                 plugin_id, source, original_width, trimmed_width,
@@ -431,7 +431,7 @@ class PluginAdapter:
         """
         if self._offset_shapes.get(plugin_id) != shape:
             if plugin_id in self._item_offsets:
-                logger.debug(
+                logger.info(
                     "[%s] Content is %s now, was %s — restarting the rotation "
                     "rather than resuming at a position that no longer means "
                     "anything", plugin_id, shape,
@@ -579,7 +579,7 @@ class PluginAdapter:
             consumed += 1
 
         if mode == 'truncate':
-            logger.debug(
+            logger.info(
                 "[%s] Width budget %dpx: showing the first %d of %d row(s) "
                 "(%dpx incl. gaps); the rest are not shown (overflow=truncate)",
                 plugin_id, budget, len(selected), len(images), used
@@ -587,7 +587,7 @@ class PluginAdapter:
         else:
             self._record_offset(
                 plugin_id, (start + consumed) % len(images), shape)
-            logger.debug(
+            logger.info(
                 "[%s] Width budget %dpx: showing %d of %d row(s) (%dpx incl. gaps) "
                 "from offset %d; remainder deferred to a later cycle",
                 plugin_id, budget, len(selected), len(images), used, start
@@ -636,7 +636,7 @@ class PluginAdapter:
             if mode != 'truncate':
                 self._record_offset(
                     plugin_id, 0 if end >= img.width else end, shape)
-            logger.debug(
+            logger.info(
                 "[%s] Width budget %dpx: cropped continuous %dpx image to "
                 "[%d:%d] (no item gaps of %dpx+ to align to)%s",
                 plugin_id, budget, img.width, offset, end, min_run,
@@ -674,7 +674,7 @@ class PluginAdapter:
             self._record_offset(
                 plugin_id, 0 if end >= img.width else end_index, shape)
 
-        logger.debug(
+        logger.info(
             "[%s] Width budget %dpx: cropped single %dpx image to [%d:%d] "
             "(%dpx) at item boundaries %d-%d of %d, %s",
             plugin_id, budget, img.width, start, end, end - start,
@@ -698,7 +698,7 @@ class PluginAdapter:
             List of images or None
         """
         try:
-            logger.debug("[%s] Native: calling get_vegas_content()", plugin_id)
+            logger.info("[%s] Native: calling get_vegas_content()", plugin_id)
 
             # Tell the plugin how much width the ticker wants it to use, and
             # narrow the canvas for the duration of the call. A plugin that
@@ -707,7 +707,7 @@ class PluginAdapter:
             # be explicit can read get_vegas_render_width().
             render_width = self.resolve_render_width(plugin, plugin_id)
             if render_width != self.display_width:
-                logger.debug(
+                logger.info(
                     "[%s] Native: requesting %dpx instead of %dpx",
                     plugin_id, render_width, self.display_width
                 )
@@ -735,19 +735,19 @@ class PluginAdapter:
                 plugin._vegas_render_width = None
 
             if result is None:
-                logger.debug("[%s] Native: get_vegas_content() returned None", plugin_id)
+                logger.info("[%s] Native: get_vegas_content() returned None", plugin_id)
                 return None
 
             # Normalize to list
             if isinstance(result, Image.Image):
                 images = [result]
-                logger.debug(
+                logger.info(
                     "[%s] Native: got single Image %dx%d",
                     plugin_id, result.width, result.height
                 )
             elif isinstance(result, (list, tuple)):
                 images = list(result)
-                logger.debug(
+                logger.info(
                     "[%s] Native: got %d items in list/tuple",
                     plugin_id, len(images)
                 )
@@ -768,14 +768,14 @@ class PluginAdapter:
                     )
                     continue
 
-                logger.debug(
+                logger.info(
                     "[%s] Native: item[%d] is %dx%d, mode=%s",
                     plugin_id, i, img.width, img.height, img.mode
                 )
 
                 # Ensure correct height
                 if img.height != self.display_height:
-                    logger.debug(
+                    logger.info(
                         "[%s] Native: resizing item[%d]: %dx%d -> %dx%d",
                         plugin_id, i, img.width, img.height,
                         img.width, self.display_height
@@ -793,13 +793,13 @@ class PluginAdapter:
 
             if valid_images:
                 total_width = sum(img.width for img in valid_images)
-                logger.debug(
+                logger.info(
                     "[%s] Native: SUCCESS - %d images, %dpx total width",
                     plugin_id, len(valid_images), total_width
                 )
                 return valid_images
 
-            logger.debug("[%s] Native: no valid images after validation", plugin_id)
+            logger.info("[%s] Native: no valid images after validation", plugin_id)
             return None
 
         except (AttributeError, TypeError, ValueError, OSError) as e:
@@ -833,20 +833,20 @@ class PluginAdapter:
                 logger.debug("[%s] No scroll_helper attribute", plugin_id)
                 return None
 
-            logger.debug(
+            logger.info(
                 "[%s] Found scroll_helper: %s",
                 plugin_id, type(scroll_helper).__name__
             )
 
             cached_image = getattr(scroll_helper, 'cached_image', None)
             if cached_image is None:
-                logger.debug(
+                logger.info(
                     "[%s] scroll_helper.cached_image is None, triggering content generation",
                     plugin_id
                 )
                 if offscreen_only:
                     # Generating it calls display(), which needs the canvas.
-                    logger.debug(
+                    logger.info(
                         "[%s] scroll_helper cache empty; deferring generation "
                         "to the render thread", plugin_id
                     )
@@ -859,13 +859,13 @@ class PluginAdapter:
                     return None
 
             if not isinstance(cached_image, Image.Image):
-                logger.debug(
+                logger.info(
                     "[%s] scroll_helper.cached_image is not an Image: %s",
                     plugin_id, type(cached_image).__name__
                 )
                 return None
 
-            logger.debug(
+            logger.info(
                 "[%s] scroll_helper.cached_image found: %dx%d, mode=%s",
                 plugin_id, cached_image.width, cached_image.height, cached_image.mode
             )
@@ -888,7 +888,7 @@ class PluginAdapter:
 
             # Ensure correct height
             if img.height != self.display_height:
-                logger.debug(
+                logger.info(
                     "[%s] Resizing scroll_helper content: %dx%d -> %dx%d",
                     plugin_id, img.width, img.height,
                     img.width, self.display_height
@@ -902,7 +902,7 @@ class PluginAdapter:
             if img.mode != 'RGB':
                 img = img.convert('RGB')
 
-            logger.debug(
+            logger.info(
                 "[%s] ScrollHelper content ready: %dx%d",
                 plugin_id, img.width, img.height
             )
@@ -1002,7 +1002,7 @@ class PluginAdapter:
             with self._capture():
                 # Method 1: Try _create_scrolling_display (stocks pattern)
                 if hasattr(plugin, '_create_scrolling_display'):
-                    logger.debug(
+                    logger.info(
                         "[%s] Triggering via _create_scrolling_display()",
                         plugin_id
                     )
@@ -1010,7 +1010,7 @@ class PluginAdapter:
                         plugin._create_scrolling_display()
                         cached_image = getattr(scroll_helper, 'cached_image', None)
                         if cached_image is not None and isinstance(cached_image, Image.Image):
-                            logger.debug(
+                            logger.info(
                                 "[%s] _create_scrolling_display() SUCCESS: %dx%d",
                                 plugin_id, cached_image.width, cached_image.height
                             )
@@ -1022,7 +1022,7 @@ class PluginAdapter:
 
                 # Method 2: Try display(force_clear=True) which typically builds scroll content
                 if hasattr(plugin, 'display'):
-                    logger.debug(
+                    logger.info(
                         "[%s] Triggering via display(force_clear=True)",
                         plugin_id
                     )
@@ -1031,12 +1031,12 @@ class PluginAdapter:
                         plugin.display(force_clear=True)
                         cached_image = getattr(scroll_helper, 'cached_image', None)
                         if cached_image is not None and isinstance(cached_image, Image.Image):
-                            logger.debug(
+                            logger.info(
                                 "[%s] display(force_clear=True) SUCCESS: %dx%d",
                                 plugin_id, cached_image.width, cached_image.height
                             )
                             return cached_image
-                        logger.debug(
+                        logger.info(
                             "[%s] display(force_clear=True) did not populate cached_image",
                             plugin_id
                         )
@@ -1045,7 +1045,7 @@ class PluginAdapter:
                             "[%s] display(force_clear=True) failed", plugin_id
                         )
 
-            logger.debug(
+            logger.info(
                 "[%s] Could not trigger scroll content generation",
                 plugin_id
             )
@@ -1077,15 +1077,15 @@ class PluginAdapter:
         try:
             # Save current display state
             original_image = self.display_manager.image.copy()
-            logger.debug("[%s] Fallback: saved original display state", plugin_id)
+            logger.info("[%s] Fallback: saved original display state", plugin_id)
 
             # Ensure plugin has fresh data before capturing
             has_update_data = hasattr(plugin, 'update_data')
-            logger.debug("[%s] Fallback: has update_data=%s", plugin_id, has_update_data)
+            logger.info("[%s] Fallback: has update_data=%s", plugin_id, has_update_data)
             if has_update_data:
                 try:
                     plugin.update_data()
-                    logger.debug("[%s] Fallback: update_data() called", plugin_id)
+                    logger.info("[%s] Fallback: update_data() called", plugin_id)
                 except (AttributeError, RuntimeError, OSError):
                     logger.exception("[%s] Fallback: update_data() failed", plugin_id)
 
@@ -1097,41 +1097,41 @@ class PluginAdapter:
             # arrangement rather than one that has to be cropped afterwards.
             render_width = self.resolve_render_width(plugin, plugin_id)
             if render_width != self.display_width:
-                logger.debug(
+                logger.info(
                     "[%s] Fallback: rendering at %dpx instead of %dpx",
                     plugin_id, render_width, self.display_width
                 )
 
             with self._capture(), self._render_at(render_width):
                 self.display_manager.clear()
-                logger.debug("[%s] Fallback: display cleared, calling display()", plugin_id)
+                logger.info("[%s] Fallback: display cleared, calling display()", plugin_id)
 
                 # First try without force_clear (some plugins behave better this way)
                 try:
                     plugin.display()
-                    logger.debug("[%s] Fallback: display() called successfully", plugin_id)
+                    logger.info("[%s] Fallback: display() called successfully", plugin_id)
                 except TypeError:
                     # Plugin may require force_clear argument
-                    logger.debug("[%s] Fallback: display() failed, trying with force_clear=True", plugin_id)
+                    logger.info("[%s] Fallback: display() failed, trying with force_clear=True", plugin_id)
                     plugin.display(force_clear=True)
 
                 # Capture the result
                 captured = self.display_manager.image.copy()
 
-            logger.debug(
+            logger.info(
                 "[%s] Fallback: captured frame %dx%d, mode=%s",
                 plugin_id, captured.width, captured.height, captured.mode
             )
 
             # Check if captured image has content (not all black)
             is_blank, bright_ratio = self._is_blank_image(captured, return_ratio=True)
-            logger.debug(
+            logger.info(
                 "[%s] Fallback: brightness check - %.3f%% bright pixels (threshold=0.5%%)",
                 plugin_id, bright_ratio * 100
             )
 
             if is_blank:
-                logger.debug(
+                logger.info(
                     "[%s] Fallback: first capture blank, retrying with force_clear",
                     plugin_id
                 )
@@ -1142,7 +1142,7 @@ class PluginAdapter:
                     captured = self.display_manager.image.copy()
 
                 is_blank, bright_ratio = self._is_blank_image(captured, return_ratio=True)
-                logger.debug(
+                logger.info(
                     "[%s] Fallback: retry brightness - %.3f%% bright pixels",
                     plugin_id, bright_ratio * 100
                 )
@@ -1159,7 +1159,7 @@ class PluginAdapter:
             if captured.mode != 'RGB':
                 captured = captured.convert('RGB')
 
-            logger.debug(
+            logger.info(
                 "[%s] Fallback: SUCCESS - captured %dx%d",
                 plugin_id, captured.width, captured.height
             )

test/test_update_check_reports_failure.py

@@ -0,0 +1,85 @@
+"""A check that could not run must not be reported as "up to date".
+
+check-update returned update_available=False whenever git failed. The banner
+is the only route to the update button, so a checkout git refuses to touch
+looked exactly like a current one -- permanently, and with nothing for the
+user to act on. The usual cause is an install performed as root, after which
+every git command fails with "detected dubious ownership".
+"""
+import subprocess
+import sys
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+from flask import Flask
+
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
+
+from web_interface.blueprints import api_v3 as mod  # noqa: E402
+from web_interface.blueprints.api_v3 import api_v3  # noqa: E402
+
+DUBIOUS = ("fatal: detected dubious ownership in repository at "
+           "'/home/pi/LEDMatrix'\nTo add an exception for this directory, call:\n"
+           "\tgit config --global --add safe.directory /home/pi/LEDMatrix\n")
+
+
+@pytest.fixture
+def client():
+    app = Flask(__name__)
+    app.config['TESTING'] = True
+    app.register_blueprint(api_v3, url_prefix='/api/v3')
+    mod._update_check_cache['result'] = None
+    mod._update_check_cache['ts'] = 0
+    return app.test_client()
+
+
+def _fetch_fails(stderr: bytes):
+    def fake_run(args, **kwargs):
+        if args[:2] == ['git', 'fetch']:
+            return subprocess.CompletedProcess(args, 1, stdout=b'', stderr=stderr)
+        return subprocess.CompletedProcess(args, 0, stdout='', stderr='')
+    return fake_run
+
+
+class TestFailedCheckIsNotSilence:
+    def test_dubious_ownership_is_reported_not_swallowed(self, client):
+        with patch.object(mod.subprocess, 'run', _fetch_fails(DUBIOUS.encode())):
+            data = client.get('/api/v3/system/check-update').get_json()
+        assert data['check_failed'] is True, (
+            "a git failure was reported as a successful 'no update' check")
+        assert data['update_available'] is False
+
+    def test_the_message_tells_the_user_what_to_do(self, client):
+        with patch.object(mod.subprocess, 'run', _fetch_fails(DUBIOUS.encode())):
+            data = client.get('/api/v3/system/check-update').get_json()
+        assert 'chown' in data['error'], (
+            "dubious ownership is unactionable without the fix command")
+        assert 'root' in data['error']
+
+    def test_an_ordinary_git_failure_still_surfaces(self, client):
+        with patch.object(mod.subprocess, 'run',
+                          _fetch_fails(b'fatal: some other git problem\n')):
+            data = client.get('/api/v3/system/check-update').get_json()
+        assert data['check_failed'] is True
+        assert 'some other git problem' in data['error']
+
+    def test_offline_reads_as_offline(self, client):
+        with patch.object(mod.subprocess, 'run',
+                          _fetch_fails(b'fatal: could not resolve host: github.com\n')):
+            data = client.get('/api/v3/system/check-update').get_json()
+        assert 'Could not reach GitHub' in data['error']
+
+
+class TestSuccessPathUnchanged:
+    def test_up_to_date_carries_no_failure_flag(self, client):
+        def fake_run(args, **kwargs):
+            if args[:2] == ['git', 'fetch']:
+                return subprocess.CompletedProcess(args, 0, stdout=b'', stderr=b'')
+            if args[:2] == ['git', 'rev-parse']:
+                return subprocess.CompletedProcess(args, 0, stdout='abc123\n', stderr='')
+            return subprocess.CompletedProcess(args, 0, stdout='0\n', stderr='')
+        with patch.object(mod.subprocess, 'run', fake_run):
+            data = client.get('/api/v3/system/check-update').get_json()
+        assert data['update_available'] is False
+        assert not data.get('check_failed'), "a healthy check must not look like a failure"

test/test_vegas_log_volume.py

@@ -1,63 +0,0 @@
-"""The Vegas content path must trace at DEBUG, not INFO.
-
-plugin_adapter narrates every step of acquiring content from every plugin --
-"Has get_vegas_content", "Native: calling get_vegas_content()", "Native content
-returned None", "Has scroll_helper", the per-item sizes -- and it does that for
-each plugin on each cycle.
-
-Measured on a live rig: 13,408 log lines an hour, of which 13,366 were INFO and
-35 were WARNING. plugin_adapter alone produced 2,457 of them. That is ~223
-lines a minute of string formatting on a Pi that is also driving the panel, all
-of it written through journald to the SD card, and it buries the 35 lines that
-actually indicate a problem.
-
-Nothing is lost by moving it to DEBUG: the 19 warning/error/exception calls in
-the module are untouched, so real failures still surface at their own level.
-
-One INFO call is deliberate and stays -- the padding-strip message chooses its
-level at runtime (`logger.warning if (left and right) else logger.info`) and
-test_vegas_plugin_adapter.py pins it.
-"""
-import ast
-from pathlib import Path
-
-import pytest
-
-ADAPTER = (Path(__file__).resolve().parent.parent / "src" / "vegas_mode"
-           / "plugin_adapter.py")
-
-
-def _info_calls(path):
-    """Direct logger.info(...) call sites in a module."""
-    tree = ast.parse(path.read_text(encoding="utf-8"))
-    found = []
-    for node in ast.walk(tree):
-        if (isinstance(node, ast.Call)
-                and isinstance(node.func, ast.Attribute)
-                and node.func.attr == "info"
-                and getattr(node.func.value, "id", None) == "logger"):
-            found.append(node.lineno)
-    return found
-
-
-def test_the_content_path_does_not_trace_at_info():
-    calls = _info_calls(ADAPTER)
-    assert not calls, (
-        "plugin_adapter should trace at DEBUG; found logger.info at lines "
-        f"{calls}. This path runs per plugin per cycle and its output goes to "
-        "the SD card via journald."
-    )
-
-
-def test_real_failures_still_have_a_level_of_their_own():
-    """Demoting the trace must not have swept up the error reporting."""
-    source = ADAPTER.read_text(encoding="utf-8")
-    loud = sum(source.count(f"logger.{level}(")
-               for level in ("warning", "error", "exception"))
-    assert loud >= 15, f"only {loud} warning/error/exception calls remain"
-
-
-def test_the_deliberate_runtime_chosen_level_survives():
-    """The padding-strip message picks its level at runtime; leave it alone."""
-    source = ADAPTER.read_text(encoding="utf-8")
-    assert "logger.warning if (left and right) else logger.info" in source

web_interface/blueprints/api_v3.py

@@ -1821,6 +1821,33 @@ def get_system_version():
 _update_check_cache: Dict[str, Any] = {'result': None, 'ts': 0.0}
 _UPDATE_CHECK_TTL = 300  # 5 minutes — avoids a git fetch on every page load
 
+def _update_check_failed(detail: str) -> Dict[str, Any]:
+    """A check that could not run is not the same as being up to date.
+
+    Reporting update_available=False on a git failure hides the banner, and
+    the banner is the only route to the update button -- so a checkout git
+    refuses to touch looks exactly like a current one, permanently. The most
+    common cause is an install performed as root: git then reports "dubious
+    ownership" and every command fails, including the fetch here.
+    """
+    return {'update_available': False, 'remote_sha': 'unknown',
+            'commits_behind': 0, 'check_failed': True, 'error': detail}
+
+
+def _describe_git_failure(stderr: str) -> str:
+    """Turn git's stderr into something the user can act on."""
+    text = (stderr or '').strip()
+    if 'dubious ownership' in text or 'detected dubious ownership' in text:
+        return ("This checkout is owned by a different user than the one "
+                "running the web interface, so git refuses to use it. It is "
+                "usually the result of installing as root. Fix the ownership "
+                "and the update will work: sudo chown -R $USER:$USER "
+                + str(PROJECT_ROOT))
+    if 'could not resolve host' in text.lower() or 'network is unreachable' in text.lower():
+        return "Could not reach GitHub to check for updates."
+    return "Could not check for updates: " + (text.splitlines()[0] if text else "git failed")
+
+
 @api_v3.route('/system/check-update', methods=['GET'])
 def check_for_update():
     """Check whether a newer LEDMatrix commit is available on origin/main."""
@@ -1836,12 +1863,13 @@ def check_for_update():
             capture_output=True, timeout=10, cwd=cwd,
         )
         if fetch_result.returncode != 0:
+            stderr = fetch_result.stderr.decode(errors='replace').strip()
             logger.warning("check-update: git fetch failed (rc=%d): %s",
-                           fetch_result.returncode,
+                           fetch_result.returncode, stderr)
-                           fetch_result.stderr.decode(errors='replace').strip())
+            failed = _update_check_failed(_describe_git_failure(stderr))
-            _update_check_cache['result'] = _safe
+            _update_check_cache['result'] = failed
             _update_check_cache['ts'] = now
-            return jsonify(_safe)
+            return jsonify(failed)
         local = subprocess.run(
             ['git', 'rev-parse', 'HEAD'],
             capture_output=True, text=True, timeout=5, cwd=cwd,
@@ -1869,7 +1897,8 @@ def check_for_update():
         return jsonify(result)
     except Exception as e:
         logger.warning("check-update failed: %s", e)
-        return jsonify(_safe)
+        return jsonify(_update_check_failed(
+            "Could not check for updates; see logs for details."))
 
 @api_v3.route('/system/action', methods=['POST'])
 def execute_system_action():

web_interface/templates/v3/base.html

@@ -1107,15 +1107,29 @@
         fetch('/api/v3/system/check-update')
             .then(function(r) { return r.json(); })
             .then(function(data) {
+                var banner = document.getElementById('update-banner');
+                var btn = document.getElementById('update-banner-btn');
+                if (data.check_failed) {
+                    // A check that could not run is not the same as being up
+                    // to date. Hiding the banner here made a checkout git
+                    // refuses to touch look permanently current, with no
+                    // route to the update button and nothing to act on.
+                    document.getElementById('update-banner-text').textContent =
+                        data.error || 'Could not check for updates.';
+                    if (btn) btn.style.display = 'none';
+                    banner.style.display = '';
+                    return;
+                }
+                if (btn) btn.style.display = '';
                 if (data.update_available && getDismissedSha() !== data.remote_sha) {
                     var n = data.commits_behind || 0;
                     var msg = 'A new LEDMatrix update is available';
                     if (n > 0) msg += ' (' + n + ' commit' + (n > 1 ? 's' : '') + ')';
                     document.getElementById('update-banner-text').textContent = msg;
-                    document.getElementById('update-banner').style.display = '';
+                    banner.style.display = '';
                     try { sessionStorage.setItem('update-sha', data.remote_sha); } catch(e) {}
                 } else {
-                    document.getElementById('update-banner').style.display = 'none';
+                    banner.style.display = 'none';
                 }
             })
             .catch(function() {});