Implement Priority 1 Finance Cluster Integration via Unified GraphQL API

[charles2ke]

Problem statement:
Build a unified GraphQL API layer that integrates three finance domains: OpenTrading, Portfolio-Watcher, and tax-break.

Requirements:

1. Define a coherent GraphQL schema for:
   • accounts
   • holdings/positions
   • trades/orders/fills
   • portfolio performance snapshots
   • tax estimation inputs/outputs
2. Add resolver architecture with modular service adapters/connectors for:
   • opentrading
   • portfolio-watcher
   • tax-break
     (use mock/default adapters if live endpoints are unavailable)
3. Normalize inconsistent upstream fields into canonical internal models.
4. Implement end-to-end query flows:
   • portfolio overview with positions and P/L
   • trade history mapped to tax-relevant events
   • tax estimate summary derived from trading activity
5. Add tests for schema/resolvers and aggregation logic.
6. Add README section: “Finance Cluster Integration (Priority 1)” with setup/run/test instructions and data-flow.

Engineering constraints:

• Modular folders per connector + shared domain model layer.
• Environment-based configuration for endpoints/credentials placeholders.
• Graceful partial-failure handling (one connector failure should not break all data).
• Add minimal caching/batching where useful.
• Preserve backward compatibility where possible; document breaking changes if needed.

Acceptance criteria:

• Build passes, tests pass.
• New cross-source queries work.
• Tax summary is traceable to underlying trade/portfolio data.
• PR includes architecture decisions + follow-up tasks.

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