diff --git a/.gitea/workflows/ci.yml b/.gitea/workflows/ci.yml
index 20282c3..3490273 100644
--- a/.gitea/workflows/ci.yml
+++ b/.gitea/workflows/ci.yml
@@ -5,11 +5,19 @@
 # for the host distro). The backend job uses the system python3 in a venv
 # instead. setup-node works because node is resolved differently.
 #
-# Three jobs run on push and pull_request:
-#   backend  - pytest (tests use in-memory SQLite via TestingConfig, so no
-#              database service is needed).
-#   naming   - the CONTRIBUTING.md naming/style gate.
-#   frontend - Vue build.
+# Jobs run on push and pull_request:
+#   backend        - pytest (tests use in-memory SQLite via TestingConfig, so no
+#                    database service is needed).
+#   naming         - the CONTRIBUTING.md naming/style gate.
+#   frontend       - Vue build.
+#   migrations-mysql - proves the REAL multi-site deploy path: a fresh
+#                    `flask db upgrade` + per-plugin install on utf8mb4 MySQL
+#                    from empty, idempotent on a second run. The pytest suite
+#                    only exercises SQLite create_all(), so without this a
+#                    regression in the Alembic chain on MySQL would ship
+#                    undetected. Needs a runner that supports service
+#                    containers; if yours does not, run these steps against a
+#                    host MySQL instead.
 
 name: CI
 
@@ -54,3 +62,60 @@ jobs:
           npm ci
           npm run build
         working-directory: frontend
+
+  migrations-mysql:
+    runs-on: ubuntu-latest
+    services:
+      mysql:
+        image: mysql:8.0
+        env:
+          MYSQL_ROOT_PASSWORD: root
+          MYSQL_DATABASE: shopdb_ci
+        ports:
+          - 3306:3306
+        options: >-
+          --health-cmd="mysqladmin ping -h localhost -uroot -proot"
+          --health-interval=5s --health-timeout=5s --health-retries=20
+    env:
+      DATABASE_URL: mysql+pymysql://root:root@127.0.0.1:3306/shopdb_ci?charset=utf8mb4
+      SECRET_KEY: ci-secret
+      JWT_SECRET_KEY: ci-jwt-secret
+    steps:
+      - name: Check out
+        uses: actions/checkout@v4
+      - name: Install dependencies
+        run: |
+          python3 -m venv .venv
+          .venv/bin/pip install --upgrade pip
+          .venv/bin/pip install -r requirements.txt
+      - name: Force utf8mb4 on the CI database
+        run: |
+          mysql -h 127.0.0.1 -uroot -proot -e \
+            "ALTER DATABASE shopdb_ci CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;"
+      - name: Fresh core upgrade from empty
+        run: .venv/bin/flask db upgrade
+      - name: Install every bundled plugin (runs its chain)
+        run: |
+          for p in computers employees geenforce knowledgebase machines \
+                   measuringtools network notifications printers slides usb warranty; do
+            .venv/bin/flask plugin install "$p"
+          done
+      - name: Assert schema built + utf8mb4, and a second upgrade is a no-op
+        run: |
+          .venv/bin/python - <<'PY'
+          from shopdb import create_app
+          from shopdb.extensions import db
+          from sqlalchemy import text
+          app = create_app()
+          with app.app_context():
+              insp = db.inspect(db.engine)
+              tables = insp.get_table_names()
+              assert len(tables) >= 70, f'only {len(tables)} tables built'
+              row = db.session.execute(text(
+                  "SELECT default_character_set_name FROM information_schema.schemata "
+                  "WHERE schema_name = 'shopdb_ci'")).first()
+              assert row[0] == 'utf8mb4', f'charset is {row[0]}, not utf8mb4'
+              print(f'OK: {len(tables)} tables, charset {row[0]}')
+          PY
+      - name: Second core upgrade must be a clean no-op
+        run: .venv/bin/flask db upgrade
diff --git a/migrations/versions/7d25_drop_redundant_indexes.py b/migrations/versions/7d25_drop_redundant_indexes.py
new file mode 100644
index 0000000..a4c49a8
--- /dev/null
+++ b/migrations/versions/7d25_drop_redundant_indexes.py
@@ -0,0 +1,57 @@
+"""Drop redundant secondary indexes duplicating a named idx_* / unique index.
+
+The DB review found five non-unique secondary indexes that duplicate an existing
+index on the same column: the auto-named ix_* from a column index=True alongside
+a named idx_* in __table_args__ (communications.assetid, and the hostname on
+computers/networkdevices/printers), plus idx_usb_serial duplicating the
+serialnumber unique index on usbdevices. Each redundant pair costs insert/update
+maintenance with zero read benefit. The models had the redundant index source
+removed; this drops the live duplicates so the schema matches the models.
+
+Idempotent (skips a missing table/index); real downgrade recreates them.
+
+Revision ID: 7d25_drop_redundant_indexes
+Revises: 7d24_customfield_searchable
+Create Date: 2026-07-13
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = '7d25_drop_redundant_indexes'
+down_revision = '7d24_customfield_searchable'
+branch_labels = None
+depends_on = None
+
+# (table, index name, columns, unique) - columns/unique used only to recreate on
+# downgrade. All non-unique; the surviving idx_* / unique index still covers each.
+_REDUNDANT = [
+    ('communications', 'ix_communications_assetid', ['assetid'], False),
+    ('computers', 'ix_computers_hostname', ['hostname'], False),
+    ('networkdevices', 'ix_networkdevices_hostname', ['hostname'], False),
+    ('printers', 'ix_printers_hostname', ['hostname'], False),
+    ('usbdevices', 'idx_usb_serial', ['serialnumber'], False),
+]
+
+
+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)
+    tables = set(insp.get_table_names())
+    for table, name, _cols, _unique in _REDUNDANT:
+        if table in tables and name in _index_names(insp, table):
+            op.drop_index(name, table_name=table)
+
+
+def downgrade():
+    bind = op.get_bind()
+    insp = sa.inspect(bind)
+    tables = set(insp.get_table_names())
+    for table, name, cols, unique in _REDUNDANT:
+        if table in tables and name not in _index_names(insp, table):
+            op.create_index(name, table, cols, unique=unique)
diff --git a/plugins/computers/models/computer.py b/plugins/computers/models/computer.py
index c435bd0..514fe2e 100644
--- a/plugins/computers/models/computer.py
+++ b/plugins/computers/models/computer.py
@@ -58,7 +58,6 @@ class Computer(BaseModel):
     # Network identity
     hostname = db.Column(
         db.String(100),
-        index=True,
         comment='Network hostname'
     )
 
diff --git a/plugins/network/models/network_device.py b/plugins/network/models/network_device.py
index 0293530..1ab6f73 100644
--- a/plugins/network/models/network_device.py
+++ b/plugins/network/models/network_device.py
@@ -58,7 +58,6 @@ class NetworkDevice(BaseModel):
     # Network identity
     hostname = db.Column(
         db.String(100),
-        index=True,
         comment='Network hostname'
     )
 
diff --git a/plugins/notifications/migrations/versions/0002_index_businessunitid.py b/plugins/notifications/migrations/versions/0002_index_businessunitid.py
new file mode 100644
index 0000000..b14d426
--- /dev/null
+++ b/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')
diff --git a/plugins/notifications/models/notification.py b/plugins/notifications/models/notification.py
index a776af5..a49832d 100644
--- a/plugins/notifications/models/notification.py
+++ b/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)
diff --git a/plugins/printers/models/printer.py b/plugins/printers/models/printer.py
index 9ece2fa..428a2f2 100644
--- a/plugins/printers/models/printer.py
+++ b/plugins/printers/models/printer.py
@@ -63,7 +63,6 @@ class Printer(BaseModel):
     # Network identity
     hostname = db.Column(
         db.String(100),
-        index=True,
         comment='Network hostname'
     )
 
diff --git a/plugins/usb/api/selfhosted.py b/plugins/usb/api/selfhosted.py
index 77d2aeb..4254da3 100644
--- a/plugins/usb/api/selfhosted.py
+++ b/plugins/usb/api/selfhosted.py
@@ -198,7 +198,7 @@ def checkout_device(device_id, data):
         override = parse_import_datetime(data.get('checkouttime'))
         if override is not None:
             eventtime = override
-    db.session.add(USBCheckout(usbdeviceid=device.usbdeviceid, machineid=0, sso=badge,
+    db.session.add(USBCheckout(usbdeviceid=device.usbdeviceid, sso=badge,
                                checkoutname=name, checkouttime=eventtime,
                                checkoutreason=data.get('reason')))
     device.ischeckedout = True
diff --git a/plugins/usb/migrations/versions/0002_drop_checkout_machineid.py b/plugins/usb/migrations/versions/0002_drop_checkout_machineid.py
new file mode 100644
index 0000000..f1861c6
--- /dev/null
+++ b/plugins/usb/migrations/versions/0002_drop_checkout_machineid.py
@@ -0,0 +1,42 @@
+"""Drop the dead usbcheckouts.machineid column (ADR-001: Machine retired).
+
+machineid was a NOT NULL soft-reference to the retired machines table; every
+new checkout stored the sentinel 0. It has no FK, no meaning under the asset
+model, and no reader. Drop it.
+
+Idempotent (skips a missing table/column). Downgrade restores it NOT NULL with
+server_default 0 so any existing rows stay valid.
+
+Revision ID: usb0002dropmachineid
+Revises: usb0001anchor
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = 'usb0002dropmachineid'
+down_revision = 'usb0001anchor'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    bind = op.get_bind()
+    insp = sa.inspect(bind)
+    if 'usbcheckouts' not in insp.get_table_names():
+        return
+    cols = {c['name'] for c in insp.get_columns('usbcheckouts')}
+    if 'machineid' in cols:
+        op.drop_column('usbcheckouts', 'machineid')
+
+
+def downgrade():
+    bind = op.get_bind()
+    insp = sa.inspect(bind)
+    if 'usbcheckouts' not in insp.get_table_names():
+        return
+    cols = {c['name'] for c in insp.get_columns('usbcheckouts')}
+    if 'machineid' not in cols:
+        op.add_column('usbcheckouts',
+                      sa.Column('machineid', sa.Integer(), nullable=False,
+                                server_default='0'))
diff --git a/plugins/usb/models/usb_device.py b/plugins/usb/models/usb_device.py
index e3367ec..c549cbb 100644
--- a/plugins/usb/models/usb_device.py
+++ b/plugins/usb/models/usb_device.py
@@ -75,7 +75,6 @@ class USBDevice(BaseModel, AuditMixin):
 
     # Indexes
     __table_args__ = (
-        db.Index('idx_usb_serial', 'serialnumber'),
         db.Index('idx_usb_checkedout', 'ischeckedout'),
         db.Index('idx_usb_type', 'usbdevicetypeid'),
         db.Index('idx_usb_currentuser', 'currentuserid'),
@@ -122,9 +121,6 @@ class USBCheckout(BaseModel):
         nullable=True
     )
 
-    # Legacy reference to machines table (kept for backward compatibility)
-    machineid = db.Column(db.Integer, nullable=False)
-
     # User info
     sso = db.Column(db.String(20), nullable=False, comment='SSO of user')
     checkoutname = db.Column(db.String(100), nullable=True, comment='Name of user')
diff --git a/shopdb/core/models/communication.py b/shopdb/core/models/communication.py
index 14b3d0c..5254d8b 100644
--- a/shopdb/core/models/communication.py
+++ b/shopdb/core/models/communication.py
@@ -32,7 +32,6 @@ class Communication(BaseModel):
         db.Integer,
         db.ForeignKey('assets.assetid'),
         nullable=True,
-        index=True,
         comment='FK to assets table (new architecture)'
     )
 
diff --git a/tests/test_plugin_migrations.py b/tests/test_plugin_migrations.py
index 845e92f..16e0269 100644
--- a/tests/test_plugin_migrations.py
+++ b/tests/test_plugin_migrations.py
@@ -52,6 +52,10 @@ EXPECTED_HEAD_REVISION['geenforce'] = 'geenforce0001baseline'
 EXPECTED_HEAD_REVISION['machines'] = 'machines0002rename'
 # employees adds the photofilename column on top of its cutover anchor.
 EXPECTED_HEAD_REVISION['employees'] = 'employees0002photo'
+# usb drops the dead usbcheckouts.machineid column on top of its anchor.
+EXPECTED_HEAD_REVISION['usb'] = 'usb0002dropmachineid'
+# notifications indexes businessunitid on top of its anchor.
+EXPECTED_HEAD_REVISION['notifications'] = 'notifications0002buidx'
 
 # Plugins built after the cutover: their 0001 baseline really creates tables the
 # core chain never owned.