test(api)+docs: assert matchedRemittance=null; fail-loud on fixture drift; tighten docstring

backend/src/cyclone/api.py

@@ -714,20 +714,16 @@ def list_claims(
 
 @app.get("/api/claims/{claim_id}")
 def get_claim_detail_endpoint(claim_id: str) -> dict:
-    """Return one claim with full drawer context.
+    """Return one claim with full drawer context (SP4).
 
-    SP4 detail-drawer endpoint. The body is the spec-shaped dict
-    produced by :meth:`CycloneStore.get_claim_detail` — header, state,
-    service lines, diagnoses, parties, validation, raw segments,
-    ``stateHistory`` (most-recent-first, capped at 50), and a
-    populated ``matchedRemittance`` block if the claim is paired.
+    Body shape is produced by :meth:`CycloneStore.get_claim_detail`:
+    header, state, service lines, diagnoses, parties, validation,
+    raw segments, ``stateHistory`` (most-recent-first, capped at 50),
+    and a populated ``matchedRemittance`` block when paired.
 
-    Path param is ``claim_id`` (not ``id``) to avoid shadowing
-    FastAPI's internal ``id`` name and to keep OpenAPI docs self-
-    describing (matches the ``/api/acks/{ack_id}`` convention from
-    SP3). Returns 404 when the claim is missing — never 500 — so the
-    UI can distinguish "claim doesn't exist" from a transient fetch
-    failure.
+    Path param is ``claim_id`` (matches the SP3 ``/api/acks/{ack_id}``
+    convention). Returns 404 — never 500 — on a missing claim so the
+    UI can distinguish "doesn't exist" from a transient fetch error.
     """
     body = store.get_claim_detail(claim_id)
     if body is None: