Build complete Market Data backed

[team2human]

@claude
Read all the documents in the planning directory, then build the complete Market Data Backed in the backend/ directory. This should include:

1. The Massive API interface
2. The unified market data interface
3. The market data simulator

Include full unit tests.

[claude]

Claude finished @team2human's task in 4m 29s —— View job • claude/issue-3-20260328-1235 • Create PR ➔

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Market Data Backend — Complete

The market data backend was fully built in PR #2 and is present on main. All components exist in backend/app/market/:

• Unified market data interface — interface.py: MarketDataSource abstract base class with start(), stop(), add_ticker(), remove_ticker(), get_tickers()
• GBM Simulator — simulator.py: GBMSimulator (Cholesky-correlated Geometric Brownian Motion, per-ticker volatility/drift, random event shocks) + SimulatorDataSource (async wrapper, background task, cache integration)
• Massive API client — massive_client.py: MassiveDataSource (Polygon.io REST polling, async thread offloading, configurable poll interval, graceful error handling)
• Price model — models.py: immutable PriceUpdate dataclass with change, change_percent, direction, to_dict()
• Thread-safe cache — cache.py: PriceCache with version counter for SSE change detection
• Factory — factory.py: create_market_data_source() selects simulator vs. Massive based on MASSIVE_API_KEY env var
• SSE streaming — stream.py: create_stream_router() for GET /api/stream/prices
• Unit tests — tests/market/: test_models.py, test_cache.py, test_simulator.py, test_simulator_source.py, test_massive.py, test_factory.py
• Add missing test_stream.py — added 9 tests covering router creation, event generation, version-based change detection, disconnect handling, empty cache, payload format validation