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# Implement Saga Pattern for Swap Operations with Recovery Mechanism ## Overview This PR refactors the swap operation implementation to use the saga pattern - a distributed transaction pattern that provides reliable transaction management through explicit state tracking and compensation-based error handling. The implementation includes a robust recovery mechanism that automatically handles swap operations interrupted by crashes, power loss, or network failures. ## What Changed **Saga Pattern Implementation:** - Introduced a strict linear state machine for swaps: `Initial` → `SetupComplete` → `Signed` → `Completed` - New modular `swap_saga` module with state validation, compensation logic, and saga orchestration - Automatic rollback of database changes on failure, ensuring atomic swap operations - Replaced previous swap implementation (`swap.rs`, `blinded_message_writer.rs`) with saga-based approach **Recovery Mechanism:** - Added `operation_id` and `operation_kind` columns to database schema for tracking which operation proofs belong to - New `recover_from_bad_swaps()` method that runs on mint startup to handle incomplete swaps - For proofs left in `PENDING` state from swap operations: - If blind signatures exist: marks proofs as `SPENT` (swap completed but not finalized) - If no blind signatures exist: removes proofs from database (swap failed partway through) - Database migrations included for both PostgreSQL and SQLite