chore: stash in-progress test edit

Captures the modified state of test_api_parse_persists.py so the
in-progress test work is preserved on the claims-unique-fix branch
as the sp-prefixed worktrees are cleaned up. The .venv and
.gitignore_local noise in the working tree are intentionally left
untracked.

backend/tests/test_api_parse_persists.py

@@ -357,3 +357,60 @@ def test_prodfile_cross_pipeline_reconciles(client: TestClient):
     assert claim_rows >= len(unique_837_pcns), (
         f"claim_rows {claim_rows} < unique_837_pcns {len(unique_837_pcns)}"
     )
+
+
+def test_409_response_includes_existing_batch_id_for_837(client: TestClient) -> None:
+    """When a CLM01 already exists in a prior batch, the 409 body has existing_batch_id."""
+    from datetime import datetime, timezone
+
+    from cyclone import db as _db
+    from cyclone.db import Batch, Claim
+
+    # Seed a prior batch with claim CLM-X.
+    with _db.SessionLocal()() as s:
+        s.add(Batch(
+            id="PRIOR", kind="837p", input_filename="prior.txt",
+            parsed_at=datetime(2026, 1, 1, tzinfo=timezone.utc),
+            raw_result_json={},
+        ))
+        s.add(Claim(id="CLM-X", batch_id="PRIOR", patient_control_number="M"))
+        s.commit()
+
+    # Build a file with two CLM* segments both using CLM-X (forces PK collision).
+    text = (
+        "ISA*00*          *00*          *ZZ*SUBMITTERID    *ZZ*RECEIVERID     "
+        "*240101*1200*^*00501*000000001*0*P*:~\n"
+        "GS*HC*SUBMITTERID*RECEIVERID*20240101*1200*1*X*005010X222A1~\n"
+        "ST*837*0001*005010X222A1~\n"
+        "BHT*0019*00*1*20240101*1200*CH~\n"
+        "NM1*41*2*SUBMITTER*****46*SUBMITTERID~\n"
+        "PER*IC*CONTACT*TE*5555555555~\n"
+        "NM1*40*2*RECEIVER*****46*RECEIVERID~\n"
+        "HL*1**20*1~\n"
+        "NM1*85*2*BILLING*****XX*1881068062~\n"
+        "N3*123 MAIN*\nN4*DENVER*CO*80202~\n"
+        "REF*EI*123456789~\n"
+        "HL*2*1*22*0~\n"
+        "SBR*P*18*******CI~\n"
+        "NM1*IL*1*DOE*JOHN****MI*M~\n"
+        "N3*456 ELM*\nN4*DENVER*CO*80202~\n"
+        "DMG*D8*19700101*M~\n"
+        "NM1*PR*2*MEDICAID*****PI*MCD~\n"
+        "CLM*CLM-X*100***11:B:1*Y*A*Y*Y~\n"
+        "LX*1~\nSV1*HC:99213*100*UN*1***1~\n"
+        "DTP*472*D8*20240101~\n"
+        "CLM*CLM-X*100***11:B:1*Y*A*Y*Y~\n"
+        "LX*2~\nSV1*HC:99213*100*UN*1***1~\n"
+        "DTP*472*D8*20240101~\n"
+        "SE*30*0001~\n"
+        "GE*1*1~\n"
+        "IEA*1*000000001~\n"
+    )
+    resp = client.post(
+        "/api/parse-837",
+        files={"file": ("dup.txt", text, "text/plain")},
+        headers={"Accept": "application/json"},
+    )
+    assert resp.status_code == 409, resp.text
+    body = resp.json()
+    assert body.get("existing_batch_id") == "PRIOR"