fix(jobs): split fp.jobs by thickness + serial on SO confirm

The _fp_auto_create_job grouping key was (recipe, part, coating).
Lines that shared all three but differed in thickness (or serial)
silently collapsed into one fp.job — the second line's thickness/SN
was lost, and any downstream cert printed the first line's values
across both batches. Silent mis-attestation = compliance hole.

Extended the key tuple to (recipe, part, coating, thickness, serial).
Single-line SOs and same-(thickness, SN) multi-line SOs collapse
identically to before. Only lines that previously merged when they
shouldn't have now split into their own fp.jobs.

TDD via test_so_confirm_splits_by_thickness:
  - seeds the part with default_process_id so both lines hit the
    `if recipe:` branch (where the bug lived — the no_recipe branch
    already split correctly per line)
  - confirms 2 jobs after action_confirm with each carrying its
    own thickness via the linked SO line

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

fusion_plating/fusion_plating_jobs/tests/test_fp_job_extensions.py

@@ -323,6 +323,82 @@ class TestSoConfirmHook(TransactionCase):
         else:
             self.skipTest('x_fc_part_catalog_id field not present')
 
+    def test_so_confirm_splits_by_thickness(self):
+        """Two lines with same recipe+part+coating but DIFFERENT thicknesses
+        must produce TWO fp.jobs — silent merge was a compliance bug (the
+        second thickness's CoC would carry the first thickness).
+
+        The bug only manifests when lines hit the `if recipe:` branch in
+        _fp_auto_create_job — without a resolved recipe, the no_recipe
+        branch already splits per line. We seed a recipe via
+        part.default_process_id so both lines resolve to the same recipe
+        and reach the buggy grouping path.
+        """
+        SOL = self.env['sale.order.line']
+        Part = self.env['fp.part.catalog']
+        Node = self.env['fusion.plating.process.node']
+        Thick = self.env['fp.coating.thickness']
+        if 'x_fc_part_catalog_id' not in SOL._fields \
+                or 'x_fc_thickness_id' not in SOL._fields \
+                or 'default_process_id' not in Part._fields:
+            self.skipTest('Sub 5 + recipe-on-part fields not present')
+
+        # Two distinct existing thicknesses. Creating them from scratch
+        # requires a coating_config → process_type chain that's too noisy
+        # for a unit test; reuse what's seeded.
+        thicknesses = Thick.search([], limit=2)
+        if len(thicknesses) < 2:
+            self.skipTest('need >= 2 fp.coating.thickness records seeded')
+        thick_a, thick_b = thicknesses[0], thicknesses[1]
+
+        # Any existing top-level recipe works — the test only needs both
+        # lines to resolve to the SAME recipe so they collide on the key.
+        recipe = Node.search([('parent_id', '=', False)], limit=1)
+        if not recipe:
+            self.skipTest('no fusion.plating.process.node records to anchor a recipe')
+
+        partner_for_part = self.env['res.partner'].create({'name': 'SplitPartner'})
+        part = Part.create({
+            'name': 'SplitPart', 'part_number': 'SP-1',
+            'partner_id': partner_for_part.id,
+            'default_process_id': recipe.id,
+        })
+
+        so = self.env['sale.order'].create({
+            'partner_id': self.partner.id,
+            'client_order_ref': 'TEST-PO-SPLIT',
+        })
+        SOL.create({
+            'order_id': so.id, 'product_id': self.product.id,
+            'product_uom_qty': 2.0, 'price_unit': 10.0,
+            'x_fc_part_catalog_id': part.id,
+            'x_fc_thickness_id': thick_a.id,
+        })
+        SOL.create({
+            'order_id': so.id, 'product_id': self.product.id,
+            'product_uom_qty': 1.0, 'price_unit': 10.0,
+            'x_fc_part_catalog_id': part.id,
+            'x_fc_thickness_id': thick_b.id,
+        })
+        so.action_confirm()
+
+        jobs = self.env['fp.job'].search([('sale_order_id', '=', so.id)])
+        self.assertEqual(
+            len(jobs), 2,
+            'Lines with different thicknesses must spawn separate fp.jobs '
+            '(both lines share recipe+part+coating, only thickness differs)',
+        )
+        # Each job's linked SO line should carry its own thickness
+        thicknesses_on_jobs = set()
+        for job in jobs:
+            for line in job.sale_order_line_ids:
+                if line.x_fc_thickness_id:
+                    thicknesses_on_jobs.add(line.x_fc_thickness_id.id)
+        self.assertEqual(
+            thicknesses_on_jobs, {thick_a.id, thick_b.id},
+            'The two distinct thicknesses must each appear on its own job',
+        )
+
 
 class TestJobLifecycleHooks(TransactionCase):
     def setUp(self):