fix: let the migration hand device.conf to the one place defaults live

classroom-migrate knew how to remove a setting, move a channel and point
a room at the broker, and knew nothing about which settings the classroom
has gained since a room was installed. That list is in
classroom_config.py and it stays there: the migration now hands the file
to ensure_device_config when its own work is done, rather than growing a
second copy of it.

It matters for the command rather than the package. postinst already
called the shared helper before running the migration, so an install
converged; a technician running `sudo classroom-migrate` by hand on an
old machine got a file that was still short of LIVE_ENABLED,
AUDIO_OUTPUT and UI_SCALE. Both paths end in the same place now, and the
release gate runs the command by hand on an already-converged machine to
prove it.

The validator's own expectation was the release-blocking failure, and it
was not what it looked like: it stops at CHANNEL=canary, before it ever
reaches the LIVE_ENABLED count. canary is the sway line, and moving a
migrated room off it is deliberate — a Plasma room left there is handed
the old desktop back by the next release published to it. The fixture now
expects the move, checks that every setting this release has arrived
exactly once, and checks it again after a reinstall.

Co-Authored-By: Claude Opus 5 <[email protected]>

tests/test-classroom-migrate-config.sh

@@ -20,6 +20,13 @@ import tempfile
 from pathlib import Path
 
 root = Path(sys.argv[1])
+sys.path.insert(0, str(root / "lib"))
+
+from classroom_config import (  # noqa: E402
+    DEVICE_CONFIG_SECTIONS,
+    ensure_device_config,
+)
+
 script = (root / "scripts/classroom-migrate").read_text()
 
 block = re.search(r'python3 - "\$DEVICE_CONFIG" <<\'PY\'\n(.*?)\nPY\n',
@@ -46,8 +53,12 @@ if block is None:
 migration = block.group(1)
 
 
-def migrate(text):
-    """Run the real migration over a device.conf and return it."""
+def migrate(text, shared=False):
+    """Run the real migration over a device.conf and return it.
+
+    With shared=True, the shared helper runs afterwards as well, which is
+    the whole sequence classroom-migrate performs.
+    """
     with tempfile.TemporaryDirectory() as directory:
         source = Path(directory) / "migrate.py"
         source.write_text(migration)
@@ -59,6 +70,9 @@ def migrate(text):
             capture_output=True, text=True, check=False,
         )
 
+        if shared:
+            ensure_device_config(config)
+
         return config.read_text(), result.stdout + result.stderr
 
 
@@ -147,6 +161,68 @@ once, _ = migrate(BEFORE)
 twice, _ = migrate(once)
 check("the second run is a no-op", once == twice)
 
+print()
+print("5. a room old enough to be missing settings this release has")
+
+# The migration knows nothing about which settings the classroom has
+# gained since a room was installed, and must not: that list lives in
+# classroom_config.py. What it has to do is hand the file to the shared
+# helper afterwards, so a machine converges whether it arrived through the
+# package's postinst or through somebody running the command by hand.
+AGED = """# A room set up a long time ago. Keep this comment.
+UPDATE_URL=https://updates.riverofglorymn.org
+CHANNEL=a-channel-somebody-named
+COMPOSITOR=hyprland
+MQTT_ENABLED=false
+MQTT_HOST=
+MQTT_USERNAME=classroom
+MQTT_PASSWORD=preserve-me
+CUSTOM_SETTING=preserve-me-too
+"""
+
+after, output = migrate(AGED, shared=True)
+
+missing = [key for key, _ in DEVICE_CONFIG_SECTIONS]
+check("there are settings for this to be about", len(missing) >= 3)
+
+for key in ("LIVE_ENABLED", "AUDIO_OUTPUT", "UI_SCALE"):
+    check(f"{key} is appended", f"\n{key}=" in "\n" + after)
+    check(f"{key} exactly once",
+          len(re.findall(rf"^{key}=", after, re.M)) == 1)
+
+check("every setting this release knows about is present",
+      all(re.search(rf"^{key}=", after, re.M) for key in missing))
+check("the room's comment survives",
+      "# A room set up a long time ago. Keep this comment." in after)
+check("the custom setting survives", "CUSTOM_SETTING=preserve-me-too" in after)
+check("the password survives", "MQTT_PASSWORD=preserve-me" in after)
+check("and is still never printed", "preserve-me" not in output)
+check("the username survives", "MQTT_USERNAME=classroom" in after)
+check("the deliberate channel is still deliberate",
+      "CHANNEL=a-channel-somebody-named" in after)
+check("the migration still did its own work",
+      "COMPOSITOR" not in after
+      and "MQTT_ENABLED=true" in after
+      and "MQTT_HOST=10.40.0.2" in after)
+
+twice, _ = migrate(after, shared=True)
+check("and running the whole thing again changes nothing", twice == after)
+
+print()
+print("6. the defaults live in one place")
+
+check("the migration does not carry a copy of them",
+      not any(key in migration
+              for key, _ in DEVICE_CONFIG_SECTIONS
+              if key not in ("MQTT_ENABLED",)))
+check("the script calls the shared helper",
+      "ensure_device_config" in script)
+check("after its own migration, not before",
+      script.index("ensure_device_config")
+      > script.index("OBSOLETE_CHANNELS"))
+check("with the file it was given",
+      "ensure_device_config(sys.argv[1])" in script)
+
 print()
 print(f"{passed} passed, {failed} failed")
 sys.exit(1 if failed else 0)