fix(api): synchronize hydraulic playback binary contract

tests/api/test_hydraulic_playback_endpoints.py

@@ -77,3 +77,10 @@ def test_cache_separates_projects_and_database_routes(monkeypatch):
     asyncio.run(run())
     assert calls == ["one", "two", "one"]
     playback._cache.clear()
+
+
+def test_contract_advertises_binary_packets_instead_of_json():
+    schema = build_test_app(playback.router, "/api/v1").openapi()
+    for suffix in ("geometry", "frames"):
+        content = schema["paths"][f"/api/v1/timeseries/realtime/playback/{suffix}"]["get"]["responses"]["200"]["content"]
+        assert content == {"application/octet-stream": {"schema": {"type": "string", "format": "binary"}}}