Read the bed temperature from the plate the project is sliced for (issue #2989)

BambuStudio writes no bed_temperature key. It stores a per-filament array per
plate type and names the fitted plate in curr_bed_type; bed_temperature is the
Orca/Prusa spelling, so the lookup matched nothing and every archive from a
Bambu slice stored NULL - 0 of 455 real 3MFs resolved. Preheat then fell back
to the keep-warm bed temperature on jobs that had one all along.

Plate names and the plate-to-key mapping are BambuStudio's own get_bed_temp_key
and get_bed_temp_1st_layer_key. First-layer value preferred, highest entry in
the per-filament array taken, an all-zero array left unrecorded.

backend/tests/unit/test_archive_bed_temperature_2989.py

@@ -0,0 +1,164 @@
+"""BambuStudio does not write a ``bed_temperature`` key, so we never read one.
+
+The 3MF stores one bed-temperature array per plate type -- ``cool_plate_temp``,
+``eng_plate_temp``, ``hot_plate_temp``, ``textured_plate_temp``,
+``supertack_plate_temp`` -- and names the plate the project is sliced for in
+``curr_bed_type``. ``bed_temperature`` is the Orca/PrusaSlicer spelling. The
+extractor looked only for that spelling, so ``PrintArchive.bed_temperature`` was
+NULL for every archive produced from a Bambu slice: measured at 0 of 455 real
+3MFs on a live install, against 455 of 455 once the plate keys are read.
+
+That NULL is not cosmetic. Preheat reads ``archive.bed_temperature`` to decide
+what to heat the bed to, and with nothing there it falls back to the configured
+chamber-heating bed temperature (90 by default) on jobs that never wanted it --
+which is how #2989's PLA print came to sit behind a 90°C bed.
+
+Key names and the plate mapping are BambuStudio's own ``get_bed_temp_key`` /
+``get_bed_temp_1st_layer_key`` (PrintConfig.hpp); the plate names are the
+``curr_bed_type`` enum values (PrintConfig.cpp).
+"""
+
+import pytest
+
+from backend.app.services.archive import ThreeMFParser
+
+
+def _extract(config: dict) -> int | None:
+    parser = ThreeMFParser.__new__(ThreeMFParser)
+    parser.metadata = {}
+    parser._extract_print_settings(config)
+    return parser.metadata.get("bed_temperature")
+
+
+class TestThePlateTheProjectIsSlicedFor:
+    @pytest.mark.parametrize(
+        "bed_type,key",
+        [
+            ("Cool Plate", "cool_plate_temp"),
+            ("Engineering Plate", "eng_plate_temp"),
+            ("High Temp Plate", "hot_plate_temp"),
+            ("Textured PEI Plate", "textured_plate_temp"),
+            ("Supertack Plate", "supertack_plate_temp"),
+        ],
+    )
+    def test_every_plate_type_reads_its_own_array(self, bed_type, key):
+        """All five plates BambuStudio can name, each with its own key."""
+        assert _extract({"curr_bed_type": bed_type, key: ["65", "65"]}) == 65
+
+    def test_the_fitted_plate_wins_over_the_others(self):
+        """The real failure mode this replaces: reading whichever key happened
+        to be present. A Textured slice must not take the cool plate's 0."""
+        config = {
+            "curr_bed_type": "Textured PEI Plate",
+            "cool_plate_temp": ["0", "0", "0"],
+            "eng_plate_temp": ["90", "90", "90"],
+            "hot_plate_temp": ["90", "90", "90"],
+            "textured_plate_temp": ["55", "55", "55"],
+            "supertack_plate_temp": ["0", "0", "0"],
+        }
+        assert _extract(config) == 55
+
+    def test_the_first_layer_value_is_preferred(self):
+        """It is what the printer heats to before the print starts, which is
+        the number preheat is trying to reach."""
+        config = {
+            "curr_bed_type": "Textured PEI Plate",
+            "textured_plate_temp_initial_layer": ["65"],
+            "textured_plate_temp": ["60"],
+        }
+        assert _extract(config) == 65
+
+    def test_the_regular_value_when_there_is_no_first_layer_one(self):
+        config = {"curr_bed_type": "Textured PEI Plate", "textured_plate_temp": ["60"]}
+        assert _extract(config) == 60
+
+
+class TestThePerFilamentArray:
+    def test_the_highest_entry_wins(self):
+        """One bed, several filaments: the print runs at the highest its
+        filaments ask for."""
+        config = {"curr_bed_type": "High Temp Plate", "hot_plate_temp": ["55", "100", "90"]}
+        assert _extract(config) == 100
+
+    def test_a_leading_zero_does_not_win(self):
+        """0 means that filament cannot print on this plate. Taking entry 0 --
+        what the neighbouring scalar settings do -- would store a cold bed for
+        any project whose first filament is not one this plate is heated for."""
+        config = {"curr_bed_type": "High Temp Plate", "hot_plate_temp": ["0", "90"]}
+        assert _extract(config) == 90
+
+    def test_a_scalar_rather_than_an_array(self):
+        assert _extract({"curr_bed_type": "Cool Plate", "cool_plate_temp": 35}) == 35
+
+    def test_numeric_strings_and_floats(self):
+        assert _extract({"curr_bed_type": "Cool Plate", "cool_plate_temp": ["35.0"]}) == 35
+
+
+class TestWhatItRefusesToInvent:
+    def test_an_all_zero_plate_array_is_not_a_bed_temperature(self):
+        """No filament in the project prints on this plate. Recording the 0
+        would read downstream as a deliberate cold bed."""
+        config = {"curr_bed_type": "Cool Plate", "cool_plate_temp": ["0", "0"]}
+        assert _extract(config) is None
+
+    def test_a_plate_bambustudio_maps_to_no_key(self):
+        """``Default Plate`` has no temperature array of its own, and guessing
+        another plate's would invent a temperature the slice never specified."""
+        config = {"curr_bed_type": "Default Plate", "hot_plate_temp": ["90"]}
+        assert _extract(config) is None
+
+    def test_a_plate_name_we_do_not_know(self):
+        """A plate a future BambuStudio adds must not silently read another
+        plate's array."""
+        config = {"curr_bed_type": "Cryo Plate", "textured_plate_temp": ["55"]}
+        assert _extract(config) is None
+
+    def test_a_config_with_no_bed_temperature_at_all(self):
+        assert _extract({"curr_bed_type": "Textured PEI Plate", "layer_height": ["0.2"]}) is None
+
+    def test_junk_entries_are_stepped_over(self):
+        config = {"curr_bed_type": "Cool Plate", "cool_plate_temp": [None, {}, "abc", "35"]}
+        assert _extract(config) == 35
+
+
+class TestOrcaExportsStillWork:
+    """The generic spelling is the fallback, not the primary -- Orca-exported
+    3MFs and anything else Prusa-shaped keep parsing exactly as before."""
+
+    def test_the_generic_first_layer_key(self):
+        assert _extract({"bed_temperature_initial_layer": ["60"]}) == 60
+
+    def test_the_generic_key(self):
+        assert _extract({"bed_temperature": 60}) == 60
+
+    def test_the_plate_array_is_preferred_when_both_are_present(self):
+        config = {
+            "curr_bed_type": "Textured PEI Plate",
+            "textured_plate_temp": ["55"],
+            "bed_temperature": ["90"],
+        }
+        assert _extract(config) == 55
+
+
+class TestTheNeighbouringSettingsAreUntouched:
+    """The same method extracts three other values; none of them changed."""
+
+    def test_nozzle_temperature_layer_height_and_diameter(self):
+        parser = ThreeMFParser.__new__(ThreeMFParser)
+        parser.metadata = {}
+        parser._extract_print_settings(
+            {
+                "curr_bed_type": "Textured PEI Plate",
+                "textured_plate_temp": ["55"],
+                "nozzle_temperature_initial_layer": ["220", "220"],
+                "layer_height": ["0.2"],
+                "nozzle_diameter": ["0.4"],
+            }
+        )
+        assert parser.metadata == {
+            "bed_type": "Textured PEI Plate",
+            "layer_height": 0.2,
+            "nozzle_diameter": 0.4,
+            "bed_temperature": 55,
+            "nozzle_temperature": 220,
+        }