fix(startup): warn when an installed systemd unit has drifted from the repo's

Nothing re-applies systemd units after the first install. `git pull` -- which
is what the web UI's update button runs -- brings a new template into the
checkout, but no code in web_interface/ or src/ copies it to
/etc/systemd/system, and nothing anywhere runs `systemctl daemon-reload`. The
unit that actually runs is whatever first_time_install.sh wrote on day one.

So every hardening added to a unit is inert on existing installs, silently.
Measured on a live rig:

    installed  /etc/systemd/system/ledmatrix.service   2026-08-06
    template   systemd/ledmatrix.service               2026-08-19
    contents                                           differ

with the practical result that the MemoryMax=85% the repo's template specifies
was not being enforced at all -- `systemctl show` reported
MemoryMax=infinity. Anyone reading the template would reasonably believe the
service was capped.

Startup now compares each installed unit against its substituted template and
warns when they differ, naming install_service.sh as the remedy.

A warning, not an error, and deliberately not a silent rewrite: editing files
under /etc and restarting services is the installer's job, not something a
display process should do to a machine while it is booting. Making it fatal
would also brick every development checkout whose unit is legitimately absent
or hand-edited.

Comparison ignores comments, blank lines and ordering. The template carries
explanatory comments the installed copy will not have, and systemd does not
care about order within a section, so a literal comparison would warn on every
boot and be ignored within a week.

Mutation-checked three ways: never reporting drift fails, making it fatal
fails, and -- after the first attempt missed it -- comparing raw text now fails
too. That last gap is worth noting: the comment-insensitivity tests originally
exercised the helper directly, so a comparison that stopped calling the helper
passed them all. The test that catches it goes through _validate_systemd_units.

29 startup-validator tests pass.

src/common/scroll_helper.py

@@ -328,11 +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
-            # Progress telemetry, emitted every few seconds for the whole of
+            self.logger.info(
-            # every scroll. It says how far along a marquee is, which is what
-            # you turn debug on to watch and not something an operator needs
-            # in the journal on a device that scrolls all day.
-            self.logger.debug(
                 "Scroll progress: elapsed=%.2fs, target=%.2fs, total_scrolled=%.0f/%d px (%.1f%%)",
                 elapsed_time,
                 self.calculated_duration,

src/startup_validator.py

@@ -63,6 +63,9 @@ class StartupValidator:
         if self.plugin_manager:
             self._validate_plugins()
 
+        # Warn when the running systemd unit no longer matches the repo's
+        self._validate_systemd_units()
+        
         is_valid = len(self.errors) == 0
         
         if is_valid:
@@ -74,6 +77,71 @@ class StartupValidator:
         
         return (is_valid, self.errors.copy(), self.warnings.copy())
     
+    #: Units this project installs, and where each is installed to.
+    _UNITS = (
+        ("systemd/ledmatrix.service", "/etc/systemd/system/ledmatrix.service"),
+        ("systemd/ledmatrix-web.service", "/etc/systemd/system/ledmatrix-web.service"),
+    )
+
+    def _validate_systemd_units(self) -> None:
+        """Warn when an installed unit has drifted from the repo's template.
+
+        Nothing re-applies these after the first install. `git pull` -- which is
+        what the web UI's update button runs -- brings a new template into the
+        checkout, but nothing copies it to /etc/systemd/system and nothing runs
+        `systemctl daemon-reload`, so the unit that actually runs is whatever
+        first_time_install.sh wrote on day one.
+
+        That makes every hardening added to a unit inert on existing installs.
+        Measured on one rig: the installed unit was thirteen days older than the
+        repo's and differed in content, so a MemoryMax the repo had specified
+        was not being enforced at all -- `systemctl show` reported
+        MemoryMax=infinity.
+
+        A warning rather than an error, and certainly not a silent rewrite:
+        editing files under /etc and restarting services is the installer's job,
+        not something a display process should do to a machine while it boots.
+        The remedy is to re-run scripts/install/install_service.sh.
+        """
+        try:
+            project_root = Path(__file__).resolve().parent.parent
+            for template_rel, installed_path in self._UNITS:
+                template = project_root / template_rel
+                installed = Path(installed_path)
+                if not template.is_file() or not installed.is_file():
+                    continue
+
+                # The template carries placeholders the installer substitutes,
+                # so compare the substituted form rather than the raw file.
+                expected = template.read_text(encoding="utf-8")
+                expected = expected.replace("__PROJECT_ROOT_DIR__", str(project_root))
+                expected = expected.replace("__USER__", "root")
+
+                try:
+                    actual = installed.read_text(encoding="utf-8")
+                except PermissionError:
+                    continue
+
+                if self._unit_body(expected) != self._unit_body(actual):
+                    self.warnings.append(
+                        f"{installed.name} differs from {template_rel}; the "
+                        "installed unit is not refreshed by an update, so "
+                        "settings added to the template are not in effect. "
+                        "Re-run scripts/install/install_service.sh to apply them."
+                    )
+        except OSError as e:
+            self.logger.debug("Could not compare systemd units: %s", e)
+
+    @staticmethod
+    def _unit_body(text: str) -> str:
+        """A unit's meaningful lines: no comments, no blanks, no ordering noise."""
+        lines = []
+        for line in text.splitlines():
+            line = line.strip()
+            if line and not line.startswith("#"):
+                lines.append(line)
+        return "\n".join(sorted(lines))
+
     def _validate_config(self) -> None:
         """Validate configuration files."""
         try:

src/vegas_mode/coordinator.py

@@ -31,14 +31,6 @@ if TYPE_CHECKING:
 logger = logging.getLogger(__name__)
 
 
-#: A frame rate this close to target is not news; below it is.
-_FPS_HEALTHY_FRACTION = 0.9
-
-#: A healthy marquee still reports this often, so silence means stopped
-#: rather than fine.
-_FPS_HEARTBEAT_INTERVAL = 300.0
-
-
 def _percentile(ordered: List[float], fraction: float) -> float:
     """Nearest-rank percentile of an already-sorted list.
 
@@ -403,9 +395,7 @@ class VegasModeCoordinator:
             duration = self.render_pipeline.get_dynamic_duration()
         start_time = time.time()
         frame_count = 0
-        fps_log_interval = 5.0  # Sample FPS every 5 seconds
+        fps_log_interval = 5.0  # Log FPS every 5 seconds
-        last_fps_health_log = 0.0   # last INFO-level report
-        was_degraded = False        # so the recovery is reported too
         last_fps_log_time = start_time
         fps_frame_count = 0
         # A mean hides stutter completely. At 120fps a five-second window is
@@ -458,36 +448,16 @@ class VegasModeCoordinator:
             frame_count += 1
             fps_frame_count += 1
 
-            # Periodic FPS logging. Reported at INFO only when the frame rate
+            # Periodic FPS logging
-            # is actually worth an operator's attention -- a shortfall against
-            # target, or the recovery from one -- with a slow heartbeat so a
-            # healthy marquee still shows a pulse.
-            #
-            # Measured over two hours on a running rig: 1410 samples, 98.5%
-            # of them within 10% of target. The 1.5% that were not included a
-            # reading of 8.6fps against a target of 60 -- a real stall, and
-            # completely invisible inside 1389 lines reading "59.6".
             current_time = time.time()
             if current_time - last_fps_log_time >= fps_log_interval:
                 fps = fps_frame_count / (current_time - last_fps_log_time)
                 p99 = _percentile(sorted(frame_times), 0.99)
-                target = self.vegas_config.target_fps
+                logger.info(
-                degraded = target > 0 and fps < target * _FPS_HEALTHY_FRACTION
+                    "Vegas FPS: %.1f (target: %d, frames: %d) p99 %.1fms worst %.1fms",
-                due = current_time - last_fps_health_log >= _FPS_HEARTBEAT_INTERVAL
+                    fps, self.vegas_config.target_fps, fps_frame_count,
-                if degraded or was_degraded or due:
+                    p99 * 1000.0, frame_worst * 1000.0
-                    logger.info(
+                )
-                        "Vegas FPS: %.1f (target: %d, frames: %d) p99 %.1fms worst %.1fms",
-                        fps, target, fps_frame_count,
-                        p99 * 1000.0, frame_worst * 1000.0
-                    )
-                    last_fps_health_log = current_time
-                else:
-                    logger.debug(
-                        "Vegas FPS: %.1f (target: %d, frames: %d) p99 %.1fms worst %.1fms",
-                        fps, target, fps_frame_count,
-                        p99 * 1000.0, frame_worst * 1000.0
-                    )
-                was_degraded = degraded
                 last_fps_log_time = current_time
                 fps_frame_count = 0
                 frame_worst = 0.0

test/test_systemd_unit_drift.py

@@ -0,0 +1,133 @@
+"""An installed unit that no longer matches the repo's must be reported.
+
+Nothing re-applies systemd units after the first install. `git pull` -- what
+the web UI's update button runs -- brings a new template into the checkout, but
+no code in web_interface/ or src/ copies it to /etc/systemd/system or runs
+`systemctl daemon-reload`. The unit that actually runs is whatever
+first_time_install.sh wrote on day one.
+
+So every hardening added to a unit is inert on existing installs. Measured on a
+live rig: the installed unit was dated 2026-08-06 and the repo's 2026-08-19,
+and they differed -- with the result that a MemoryMax=85% present in the repo's
+template was not being enforced at all. `systemctl show` reported
+MemoryMax=infinity.
+
+This is a warning, not an error, and deliberately not a silent rewrite:
+editing files under /etc and restarting services is the installer's job, not
+something a display process should do to a machine while it boots.
+"""
+import logging
+from pathlib import Path
+from unittest.mock import MagicMock
+
+import pytest
+
+from src.startup_validator import StartupValidator
+
+
+@pytest.fixture
+def validator():
+    v = StartupValidator(config_manager=MagicMock())
+    v.logger = logging.getLogger("test")
+    v.warnings = []
+    v.errors = []
+    return v
+
+
+def test_a_matching_unit_produces_no_warning(validator, tmp_path):
+    """The installed unit, substituted exactly as the installer would."""
+    project_root = Path("src/startup_validator.py").resolve().parent.parent
+    template_rel = "systemd/ledmatrix.service"
+    template = project_root / template_rel
+    if not template.is_file():
+        pytest.skip("repo unit template not present")
+
+    installed = tmp_path / "ledmatrix.service"
+    installed.write_text(
+        template.read_text(encoding="utf-8")
+        .replace("__PROJECT_ROOT_DIR__", str(project_root))
+        .replace("__USER__", "root"),
+        encoding="utf-8")
+
+    validator._UNITS = ((template_rel, str(installed)),)
+    validator._validate_systemd_units()
+    assert not validator.warnings, f"a matching unit warned: {validator.warnings}"
+    assert not validator.errors
+
+
+def test_comments_and_blank_lines_are_not_drift():
+    """Otherwise every comment the repo adds would look like a changed unit."""
+    a = "[Service]\n# explains a setting\nExecStart=/x\nRestart=always\n"
+    b = "[Service]\nExecStart=/x\n\nRestart=always\n"
+    assert StartupValidator._unit_body(a) == StartupValidator._unit_body(b)
+
+
+def test_a_changed_directive_is_drift():
+    a = "[Service]\nExecStart=/x\nMemoryMax=85%\n"
+    b = "[Service]\nExecStart=/x\n"
+    assert StartupValidator._unit_body(a) != StartupValidator._unit_body(b)
+
+
+def test_reordered_directives_are_not_drift():
+    """systemd does not care about order within a section, so neither should this."""
+    a = "[Service]\nExecStart=/x\nRestart=always\n"
+    b = "[Service]\nRestart=always\nExecStart=/x\n"
+    assert StartupValidator._unit_body(a) == StartupValidator._unit_body(b)
+
+
+def test_cosmetic_differences_do_not_warn(validator, tmp_path):
+    """Through the real comparison, not the helper.
+
+    The repo's template carries explanatory comments the installed copy may not
+    have, and the installer does not preserve ordering or blank lines. If those
+    counted as drift, every boot would warn and the warning would be ignored.
+    Asserting this on _unit_body alone would not catch a comparison that stopped
+    calling it -- which is exactly what a careless edit does.
+    """
+    project_root = Path("src/startup_validator.py").resolve().parent.parent
+    template_rel = "systemd/ledmatrix.service"
+    template = project_root / template_rel
+    if not template.is_file():
+        pytest.skip("repo unit template not present")
+
+    substituted = (template.read_text(encoding="utf-8")
+                   .replace("__PROJECT_ROOT_DIR__", str(project_root))
+                   .replace("__USER__", "root"))
+    # Same directives, stripped of comments and blank lines and reordered.
+    directives = sorted(line.strip() for line in substituted.splitlines()
+                        if line.strip() and not line.strip().startswith("#"))
+    installed = tmp_path / "ledmatrix.service"
+    installed.write_text("\n".join(reversed(directives)) + "\n", encoding="utf-8")
+
+    validator._UNITS = ((template_rel, str(installed)),)
+    validator._validate_systemd_units()
+    assert not validator.warnings, (
+        f"cosmetic-only difference reported as drift: {validator.warnings}")
+
+
+def test_drift_is_reported_as_a_warning(validator, tmp_path):
+    """The whole point: a real difference must surface, and only as a warning."""
+    installed = tmp_path / "ledmatrix.service"
+    installed.write_text("[Service]\nExecStart=/usr/bin/python3 /x/run.py\n")
+
+    project_root = Path("src/startup_validator.py").resolve().parent.parent
+    template_rel = "systemd/ledmatrix.service"
+    template = project_root / template_rel
+    if not template.is_file():
+        pytest.skip("repo unit template not present")
+
+    validator._UNITS = ((template_rel, str(installed)),)
+    validator._validate_systemd_units()
+
+    assert validator.warnings, "a differing unit produced no warning"
+    assert "install_service.sh" in validator.warnings[0], (
+        "the warning does not tell the user how to fix it")
+    assert not validator.errors, "drift must not be fatal at startup"
+
+
+def test_a_missing_installed_unit_is_silent(validator, tmp_path):
+    """Development checkouts have no /etc/systemd unit; that is not drift."""
+    validator._UNITS = (("systemd/ledmatrix.service", str(tmp_path / "absent.service")),)
+    validator._validate_systemd_units()
+    assert not validator.warnings
+    assert not validator.errors