fix(install): render the systemd units from their templates, not from heredocs (#547)

* fix(install): render the systemd units from their templates, not from heredocs

The installers carried their own inline copies of units that also exist as
templates under systemd/, and the copies drifted.

install_service.sh renders ledmatrix.service from the template correctly, then
wrote ledmatrix-web.service from a heredoc that predated it -- missing
Wants=network-online.target, RestartSec=10, SyslogIdentifier, CacheDirectory,
CacheDirectoryMode and Environment=USE_THREADING=1. install_web_service.sh had
a third copy, and install_wifi_monitor.sh a fourth, that one already differing
from its template (syslog where the template says journal).

startup_validator.py compares the installed unit against the template, so a
rig installed this way warned on every boot -- and the remedy the warning
names, "re-run scripts/install/install_service.sh", reinstalled the same stale
copy. The warning could never clear. Reproduced on a live rig running exactly
that unit.

All three installers now render systemd/*.service through the same placeholder
substitution. The template gains a __USER__ placeholder rather than hardcoding
User=root, because the web interface runs as whoever installed it.

That last point was a second, independent cause of a permanent warning: the
validator substituted a fixed "root", so any non-root install reported drift
forever. It now reads User= from the installed unit -- an install-time
decision, not something the template dictates -- and compares everything else
strictly. first_time_install.sh already reads the installed User= the same way.

Tests cover a non-root web unit not warning, a genuinely changed directive in
that unit still warning, the User= fallback, and a grep-based guard that no
installer under scripts/install/ contains an inline unit body. That guard is
what found the install_wifi_monitor.sh copy.

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

* fix(install): escape sed replacements, use mktemp, and make render failures fatal

Address CodeRabbit findings on install_service.sh, install_web_service.sh and
install_wifi_monitor.sh:

- Values interpolated into each script's sed expression (project root path,
  username) were not escaped, so a value containing &, \ or the | delimiter
  would corrupt the rendered systemd unit. Add a shared
  sed_escape_replacement() helper in the new scripts/install/lib_systemd_render.sh
  (sourced by all three scripts) and apply it to every sed replacement.
- install_service.sh rendered the main and web units to the predictable path
  /tmp/ledmatrix.service.tmp before installing them -- a symlink/TOCTOU race
  (CWE-377). Use mktemp for both, with a trap to clean up on exit.
- install_service.sh treated a missing template as a mere warning and then
  checked only whether a unit already existed at the destination before
  enabling/starting it, so a render failure could silently fall back to
  enabling a stale, previously-installed unit. Both unit blocks now exit
  non-zero on a missing template or a failed render.

Also rename the ambiguous loop variable `l` to `line` in
test/test_systemd_unit_drift.py (Ruff E741); ruff isn't wired into any CI
workflow in this repo today, so this isn't currently CI-blocking, but the
rename is trivial and correct regardless.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S3bPMESe2TfrGvbs1ef9c5

* test(install): cover sed_escape_replacement against sed-special characters

CodeRabbit asked for regression coverage using a project path containing an
ampersand; the earlier commits on this branch already fixed the escaping,
mktemp usage, and enable/start-on-fatal-render-failure findings, and the
l->line rename was already applied -- this closes the one remaining gap.

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

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/startup_validator.py

@@ -111,17 +111,25 @@ class StartupValidator:
                 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
 
+                # 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))
+                # User= is an install-time decision, not something the template
+                # dictates: the installers write whoever ran them, which on a
+                # non-root install is never "root". Substituting a fixed "root"
+                # here reported drift on every such install, permanently -- and
+                # re-running the installer, which is what the warning tells you
+                # to do, could not clear it. Taking the installed unit's own
+                # value keeps the comparison on the directives the template
+                # actually controls.
+                expected = expected.replace("__USER__", self._installed_user(actual))
+
                 if self._unit_body(expected) != self._unit_body(actual):
                     self.warnings.append(
                         f"{installed.name} differs from {template_rel}; the "
@@ -132,6 +140,19 @@ class StartupValidator:
         except OSError as e:
             self.logger.debug("Could not compare systemd units: %s", e)
 
+    @staticmethod
+    def _installed_user(unit_text: str) -> str:
+        """The installed unit's ``User=``, or "root" when it does not set one.
+
+        systemd itself defaults to root for a system unit with no User=, so that
+        is the right fallback rather than an empty string.
+        """
+        for line in unit_text.splitlines():
+            stripped = line.strip()
+            if stripped.startswith("User="):
+                return stripped.split("=", 1)[1].strip()
+        return "root"
+
     @staticmethod
     def _unit_body(text: str) -> str:
         """A unit's meaningful lines, in order: no comments, no blanks.