test(compose): report the actual status when the idempotency conflict check fails

The ERR trap added in 432e5a11 located the CI failure at the
`[[ "$conflict_status" == 409 ]]` assertion, but the request discarded
its body and the assertion printed nothing, so three failing runs never
revealed what the API actually returned.

Print the status and body on mismatch.

scripts/verify_allocated_compose.sh

@@ -146,12 +146,23 @@ queue_revision="$(python3 -c 'import json,sys; print(json.load(sys.stdin)["revis
 
 # Reusing a queue idempotency key with different command material must not
 # silently turn into a second ticket or a successful replay.
-conflict_status="$(curl -sS -o /dev/null -w '%{http_code}' -X POST "$api_url/v1/queue" \
+conflict_body="$(mktemp)"
+conflict_status="$(curl -sS -o "$conflict_body" -w '%{http_code}' -X POST "$api_url/v1/queue" \
   -H "Authorization: Bearer $access_token" \
   -H 'Idempotency-Key: compose-queue-key-123456' \
   -H 'Content-Type: application/json' \
   -d '{"ticket_id":"compose-other-ticket","playlist":"casual","client_build":"build-1","protocol_version":1}')"
-[[ "$conflict_status" == 409 ]]
+if [[ "$conflict_status" != 409 ]]; then
+  # Report what actually came back. A bare [[ ]] here just aborts, which is
+  # how this assertion failed in CI three times without ever saying what the
+  # status was.
+  echo "idempotency conflict returned ${conflict_status}, want 409; body:" >&2
+  cat "$conflict_body" >&2 || true
+  echo >&2
+  rm -f "$conflict_body"
+  exit 1
+fi
+rm -f "$conflict_body"
 
 heartbeat_json="$(curl -fsS -X POST "$api_url/v1/queue/compose-queue-ticket/heartbeat" \
   -H "Authorization: Bearer $access_token" \