DB review fixes: drop redundant indexes + dead column, add CI MySQL-upgrade job

From the database review (verdict: sound-with-minor-issues). Applies the
actionable findings.

Redundant indexes: five non-unique secondary indexes duplicated a named idx_*
or a unique index on the same column - ix_communications_assetid,
ix_computers_hostname, ix_networkdevices_hostname, ix_printers_hostname (each
shadowing an idx_*), and idx_usb_serial (shadowing the serialnumber unique
index). Removed the redundant index source from the models (column index=True /
the extra db.Index) and added core migration 7d25 dropping the live duplicates.
The unique ix_*_assetid indexes are kept (they enforce assetid uniqueness).

Dead column: usbcheckouts.machineid was a NOT NULL soft-ref to the retired
machines table storing sentinel 0 (ADR-001). Dropped from the model + the
machineid=0 literal in selfhosted checkout; usb plugin migration 0002 drops it
live (downgrade restores it default 0).

Index: notifications.businessunitid (filtered by the shopfloor feed) was
unindexed; added index=True + notifications migration 0002.

CI: new migrations-mysql job proves the real multi-site deploy path - fresh
`flask db upgrade` + per-plugin install on utf8mb4 MySQL from empty, asserting
table count + charset and a clean second-run no-op. The pytest suite only
exercises SQLite create_all(), so a regression in the Alembic chain on MySQL
would otherwise ship undetected.

Verified: fresh core upgrade on a scratch utf8mb4 MySQL builds clean + no-op on
rerun (redundant indexes absent, unique assetid kept); plugin migrations applied
+ verified on the dev DB (machineid gone, bu index present). 953 backend tests
pass; naming + pyflakes green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

plugins/notifications/migrations/versions/0002_index_businessunitid.py

@@ -0,0 +1,42 @@
+"""Index notifications.businessunitid (shopfloor list route filters on it).
+
+businessunitid is a soft-ref column the shopfloor feed filters by; it had no
+index. Add ix_notifications_businessunitid (matches the model's index=True).
+
+Idempotent; downgrade drops it.
+
+Revision ID: notifications0002buidx
+Revises: notifications0001anchor
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = 'notifications0002buidx'
+down_revision = 'notifications0001anchor'
+branch_labels = None
+depends_on = None
+
+_INDEX = 'ix_notifications_businessunitid'
+
+
+def _index_names(insp, table):
+    return {i['name'] for i in insp.get_indexes(table)}
+
+
+def upgrade():
+    bind = op.get_bind()
+    insp = sa.inspect(bind)
+    if 'notifications' not in insp.get_table_names():
+        return
+    if _INDEX not in _index_names(insp, 'notifications'):
+        op.create_index(_INDEX, 'notifications', ['businessunitid'])
+
+
+def downgrade():
+    bind = op.get_bind()
+    insp = sa.inspect(bind)
+    if 'notifications' not in insp.get_table_names():
+        return
+    if _INDEX in _index_names(insp, 'notifications'):
+        op.drop_index(_INDEX, table_name='notifications')

plugins/notifications/models/notification.py

@@ -69,7 +69,7 @@ class Notification(db.Model):
         db.ForeignKey('notificationtypes.notificationtypeid'),
         nullable=True
     )
-    businessunitid = db.Column(db.Integer, nullable=True)
+    businessunitid = db.Column(db.Integer, nullable=True, index=True)
     appid = db.Column(db.Integer, nullable=True)
     notification = db.Column(db.Text, nullable=False, comment='The message content')
     starttime = db.Column(db.DateTime, nullable=True)