fix: scope sample assertions, normalize existing_keys case, broaden row catch

- Volume/volume_unit test assertions query by scenario sample_ids
- existing_keys set lowercases DB values to match global_id_str normalization
- Per-row catch broadened to Exception with logger.exception() for tracebacks
- Analysis method tracking scoped to scenario samples
- Migration FK drop guarded against missing name entries
- Resolve stash merge conflicts in sample volume steps

Refs #558

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: kbighorse

tests/features/steps/chemistry-backfill.py

@@ -543,30 +543,27 @@ def step_then_obs_by_gid_no_extra_columns(context: Context, global_id: str):
 @then("the Sample should set volume to {value}")
 def step_then_sample_volume(context: Context, value: str):
     expected = float(value)
+    scenario_sample_ids = context._backfill_created.get("sample_ids", [])
+    assert scenario_sample_ids, "No sample_ids tracked for this scenario"
     with session_ctx() as session:
-        # Find the sample that was just modified
-        samples = (
-            session.execute(select(Sample).where(Sample.volume.isnot(None)))
-            .scalars()
-            .all()
-        )
-        assert len(samples) >= 1, "Expected at least one Sample with volume set"
-        sample = samples[-1]
+        sample = session.execute(
+            select(Sample).where(Sample.id.in_(scenario_sample_ids))
+        ).scalars().first()
+        assert sample is not None, "No Sample found for this scenario"
         assert (
             sample.volume == expected
         ), f"Expected volume={expected}, got {sample.volume}"
 
 
 @then('the Sample should set volume_unit to "{unit}"')
 def step_then_sample_volume_unit(context: Context, unit: str):
+    scenario_sample_ids = context._backfill_created.get("sample_ids", [])
+    assert scenario_sample_ids, "No sample_ids tracked for this scenario"
     with session_ctx() as session:
-        samples = (
-            session.execute(select(Sample).where(Sample.volume_unit.isnot(None)))
-            .scalars()
-            .all()
-        )
-        assert len(samples) >= 1, "Expected at least one Sample with volume_unit set"
-        sample = samples[-1]
+        sample = session.execute(
+            select(Sample).where(Sample.id.in_(scenario_sample_ids))
+        ).scalars().first()
+        assert sample is not None, "No Sample found for this scenario"
         assert (
             sample.volume_unit == unit
         ), f"Expected volume_unit='{unit}', got '{sample.volume_unit}'"

transfers/backfill/chemistry_backfill.py

@@ -127,7 +127,7 @@ def _backfill_radionuclides_impl(session: Session) -> BackfillResult:
 
     # Track existing observation keys so we know insert vs update
     existing_keys = set(
-        row[0]
+        row[0].lower() if row[0] else row[0]
         for row in session.execute(
             select(Observation.nma_pk_chemistryresults).where(
                 Observation.nma_pk_chemistryresults.isnot(None)