Build complete Market Data backend

[RuquiaAlam]

@claude
Read all the documents in the planning directory, then build the complete Market Data backend 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

[RuquiaAlam]

@claude

[RuquiaAlam]

@claude

[claude]

Claude finished @RuquiaAlam's task in 1m 4s —— View job

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Task List

• Read planning docs and repo structure
• Check current state of backend/app/market/ and tests
• Verify the market data backend is complete
• Report findings

Finding: This has already been built

The complete Market Data backend requested in this issue already exists on main (merged in PR #1, commit a58a851) — there's nothing left to implement.

backend/app/market/ contains all three pieces requested:

1. Massive API interface — massive_client.py (MassiveDataSource, REST polling client for Polygon.io via the massive package)
2. Unified market data interface — interface.py (MarketDataSource ABC) + factory.py (create_market_data_source(), selects simulator vs. Massive based on MASSIVE_API_KEY)
3. Market data simulator — simulator.py (GBMSimulator — Geometric Brownian Motion with Cholesky-correlated moves + random shock events, SimulatorDataSource)

Supporting modules: models.py (PriceUpdate), cache.py (thread-safe PriceCache), seed_prices.py, stream.py (SSE endpoint factory).

Full unit tests are in backend/tests/market/ — 6 test modules (~730 lines) covering models, cache, simulator, simulator-backed data source, factory selection logic, and the Massive client (mocked). Per planning/MARKET_DATA_SUMMARY.md, this suite has 73 passing tests at 84% coverage, and already went through a code review with all 7 identified issues resolved.

I wasn't able to actually execute pytest in this sandbox to re-verify the numbers myself — python3/pip invocations aren't in this workflow's allowed tools, only git. If you'd like me to re-run and re-verify the suite, add Bash(python3:*) or Bash(uv:*) to --allowedTools and re-trigger. I did confirm via git log that these files are committed on main and inspected the source directly to confirm it's a real, substantial implementation (not stubs) matching the three requested components.

No code changes were made — since the requested work is already done, there's nothing to branch/PR for this issue. Recommend closing #5, or let me know if you had something more specific in mind (e.g., extending the simulator, wiring it into API routes, etc.) and I'll pick that up as a follow-up.