fix(archives): assign printer_id when reusing VP-queue archives in print-start (#1403 follow-up)

  VP-queue archives are created with printer_id=None at queue-add
  time because the scheduler hasn't picked a printer yet (and even
  for explicit-printer queue items, the archive predates dispatch).
  on_print_start's expected-archive branch updated status,
  started_at, and subtask_id but never assigned printer_id, so
  VP-queue-dispatched archives stayed permanently unassigned.

  That broke every UI/API path gated on archive.printer_id —
  critically the post-print "Scan for timelapse" action: the
  H.264 file is on the printer's SD card and reachable via the
  file browser, but the archive's scan endpoint refused the request
  and the button stayed greyed out forever.

  One-line fix: archive.printer_id = printer_id in the
  expected-archive branch. Guarded against clobbering an
  already-correct value so library-file queue items (which create
  their archive with the printer pre-assigned) are idempotent.

backend/app/main.py

@@ -2016,6 +2016,15 @@ async def on_print_start(printer_id: int, data: dict):
                 archive.started_at = datetime.now(timezone.utc)
                 if subtask_id and not archive.subtask_id:
                     archive.subtask_id = subtask_id
+                # #1403 follow-up: VP-queue archives are created with
+                # printer_id=None at queue-add time (we don't know which
+                # printer will run the job yet). When the print actually
+                # starts on a specific printer the expected-archive lookup
+                # used to skip this assignment, leaving printer_id=None
+                # forever — which then disables the "Scan for timelapse"
+                # button in ArchivesPage (gated on !archive.printer_id).
+                if archive.printer_id != printer_id:
+                    archive.printer_id = printer_id
                 await db.commit()
 
                 # Track as active print

backend/tests/unit/test_print_start_assigns_printer_id_to_vp_archive.py

@@ -0,0 +1,207 @@
+"""Regression for #1403 follow-up: when on_print_start reuses a VP-queue archive,
+it must assign archive.printer_id so the post-print "Scan for timelapse" path
+in the archive UI isn't disabled forever.
+
+Reporter @pwostran and @enjoylifenow both saw "Scan for timelapse" greyed out on
+archives that came from the VP print-queue flow even though the H.264 timelapse
+was sitting on the printer's SD card. The frontend gates that button on
+``!archive.printer_id`` (ArchivesPage.tsx:459). VP-queue archives are created
+with ``printer_id=None`` at queue-add time because we don't know which printer
+will run the job yet; the print-start handler's expected-archive branch updated
+status / started_at / subtask_id but never set printer_id, so the archive stayed
+unassigned forever.
+"""
+
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+from backend.app.main import (
+    _active_prints,
+    _expected_print_creators,
+    _expected_print_registered_at,
+    _expected_prints,
+    _print_ams_mappings,
+    register_expected_print,
+)
+
+
+@pytest.fixture(autouse=True)
+def _clear_dicts():
+    _expected_prints.clear()
+    _expected_print_registered_at.clear()
+    _expected_print_creators.clear()
+    _print_ams_mappings.clear()
+    _active_prints.clear()
+    yield
+    _expected_prints.clear()
+    _expected_print_registered_at.clear()
+    _expected_print_creators.clear()
+    _print_ams_mappings.clear()
+    _active_prints.clear()
+
+
+@pytest.mark.asyncio
+async def test_expected_archive_path_assigns_printer_id_when_unset():
+    """VP-queue archives land here with printer_id=None and must be promoted
+    to the printer that actually started the job. Without this the
+    /archives/{id}/timelapse/scan endpoint refuses the request (it requires
+    archive.printer_id) and the UI button stays disabled."""
+    mock_printer = MagicMock()
+    mock_printer.id = 1
+    mock_printer.auto_archive = True
+    mock_printer.external_camera_enabled = False
+    mock_printer.external_camera_url = None
+    mock_printer.name = "TestP1S"
+
+    # VP-queue archive: printer_id is None — this is the bug surface.
+    mock_archive = MagicMock()
+    mock_archive.id = 42
+    mock_archive.filename = "bambu_lab_a1_tool_plate_3.gcode.3mf"
+    mock_archive.subtask_id = None
+    mock_archive.print_time_seconds = None
+    mock_archive.created_by_id = None
+    mock_archive.printer_id = None
+    mock_archive.print_name = "A1 Tool Plate 3"
+    mock_archive.status = "archived"
+    mock_archive.file_path = "/tmp/fake.3mf"
+    mock_archive.energy_start_kwh = None
+
+    register_expected_print(1, "bambu_lab_a1_tool_plate_3.gcode.3mf", archive_id=42, ams_mapping=None)
+
+    def execute_router(stmt, *args, **kwargs):
+        sql = str(stmt).lower()
+        if "from printers" in sql or "from printer " in sql:
+            return MagicMock(
+                scalar_one_or_none=MagicMock(return_value=mock_printer),
+                scalars=MagicMock(return_value=MagicMock(all=MagicMock(return_value=[mock_printer]))),
+            )
+        if "from print_archives" in sql or "from print_archive" in sql:
+            return MagicMock(
+                scalar_one_or_none=MagicMock(return_value=mock_archive),
+                scalars=MagicMock(return_value=MagicMock(all=MagicMock(return_value=[mock_archive]))),
+            )
+        return MagicMock(
+            scalar_one_or_none=MagicMock(return_value=None),
+            scalars=MagicMock(return_value=MagicMock(all=MagicMock(return_value=[]))),
+        )
+
+    mock_session = AsyncMock()
+    mock_session.__aenter__ = AsyncMock(return_value=mock_session)
+    mock_session.__aexit__ = AsyncMock()
+    mock_session.execute = AsyncMock(side_effect=execute_router)
+    mock_session.commit = AsyncMock()
+
+    with (
+        patch("backend.app.main.async_session") as mock_session_maker,
+        patch("backend.app.main.notification_service") as mock_notif,
+        patch("backend.app.main.smart_plug_manager") as mock_plug,
+        patch("backend.app.main.ws_manager") as mock_ws,
+        patch("backend.app.main.printer_manager") as mock_pm,
+        patch("backend.app.main.mqtt_relay") as mock_relay,
+        patch("backend.app.main._record_energy_start", new_callable=AsyncMock),
+        patch("backend.app.main._load_objects_from_archive"),
+        patch("backend.app.main._store_spoolman_print_data", new_callable=AsyncMock),
+        patch("backend.app.main._send_print_start_notification", new_callable=AsyncMock),
+    ):
+        mock_session_maker.return_value = mock_session
+        mock_notif.on_print_start = AsyncMock()
+        mock_plug.on_print_start = AsyncMock()
+        mock_ws.send_print_start = AsyncMock()
+        mock_ws.send_archive_updated = AsyncMock()
+        mock_relay.on_print_start = AsyncMock()
+        mock_pm.get_printer = MagicMock(return_value=MagicMock(name="Test", serial_number="TEST123"))
+
+        from backend.app.main import on_print_start
+
+        await on_print_start(
+            1,
+            {
+                "filename": "bambu_lab_a1_tool_plate_3.gcode.3mf",
+                "subtask_name": "bambu_lab_a1_tool_plate_3",
+            },
+        )
+
+        assert mock_archive.printer_id == 1, (
+            "expected-archive branch must assign the running printer_id so the "
+            "post-print timelapse-scan path (gated on archive.printer_id) works"
+        )
+        assert mock_archive.status == "printing"
+
+
+@pytest.mark.asyncio
+async def test_expected_archive_path_preserves_existing_printer_id():
+    """Defensive: if the archive already carries a printer_id (e.g. a
+    library-file-based queue item created with the printer pre-assigned),
+    don't clobber it with a stale value. The branch is idempotent on
+    correct data."""
+    mock_printer = MagicMock()
+    mock_printer.id = 7
+    mock_printer.auto_archive = True
+    mock_printer.external_camera_enabled = False
+    mock_printer.external_camera_url = None
+    mock_printer.name = "TestP1S"
+
+    mock_archive = MagicMock()
+    mock_archive.id = 99
+    mock_archive.filename = "MyModel.3mf"
+    mock_archive.subtask_id = None
+    mock_archive.print_time_seconds = None
+    mock_archive.created_by_id = None
+    mock_archive.printer_id = 7  # already correct
+    mock_archive.print_name = "MyModel"
+    mock_archive.status = "archived"
+    mock_archive.file_path = "/tmp/fake.3mf"
+    mock_archive.energy_start_kwh = None
+
+    register_expected_print(7, "MyModel.3mf", archive_id=99, ams_mapping=None)
+
+    def execute_router(stmt, *args, **kwargs):
+        sql = str(stmt).lower()
+        if "from printers" in sql or "from printer " in sql:
+            return MagicMock(
+                scalar_one_or_none=MagicMock(return_value=mock_printer),
+                scalars=MagicMock(return_value=MagicMock(all=MagicMock(return_value=[mock_printer]))),
+            )
+        if "from print_archives" in sql or "from print_archive" in sql:
+            return MagicMock(
+                scalar_one_or_none=MagicMock(return_value=mock_archive),
+                scalars=MagicMock(return_value=MagicMock(all=MagicMock(return_value=[mock_archive]))),
+            )
+        return MagicMock(
+            scalar_one_or_none=MagicMock(return_value=None),
+            scalars=MagicMock(return_value=MagicMock(all=MagicMock(return_value=[]))),
+        )
+
+    mock_session = AsyncMock()
+    mock_session.__aenter__ = AsyncMock(return_value=mock_session)
+    mock_session.__aexit__ = AsyncMock()
+    mock_session.execute = AsyncMock(side_effect=execute_router)
+    mock_session.commit = AsyncMock()
+
+    with (
+        patch("backend.app.main.async_session") as mock_session_maker,
+        patch("backend.app.main.notification_service") as mock_notif,
+        patch("backend.app.main.smart_plug_manager") as mock_plug,
+        patch("backend.app.main.ws_manager") as mock_ws,
+        patch("backend.app.main.printer_manager") as mock_pm,
+        patch("backend.app.main.mqtt_relay") as mock_relay,
+        patch("backend.app.main._record_energy_start", new_callable=AsyncMock),
+        patch("backend.app.main._load_objects_from_archive"),
+        patch("backend.app.main._store_spoolman_print_data", new_callable=AsyncMock),
+        patch("backend.app.main._send_print_start_notification", new_callable=AsyncMock),
+    ):
+        mock_session_maker.return_value = mock_session
+        mock_notif.on_print_start = AsyncMock()
+        mock_plug.on_print_start = AsyncMock()
+        mock_ws.send_print_start = AsyncMock()
+        mock_ws.send_archive_updated = AsyncMock()
+        mock_relay.on_print_start = AsyncMock()
+        mock_pm.get_printer = MagicMock(return_value=MagicMock(name="Test", serial_number="TEST123"))
+
+        from backend.app.main import on_print_start
+
+        await on_print_start(7, {"filename": "MyModel.3mf", "subtask_name": "MyModel"})
+
+        assert mock_archive.printer_id == 7
+        assert mock_archive.status == "printing"