Fix: PG::TRDeadlockDetected (MAYBE-RAILS-CE)

[revise-dev]

The deadlock issue occurs during concurrent inserts into the transfers table due to the unique index on inflow/outflow transaction IDs. When multiple processes try to create transfers simultaneously, they can attempt to acquire locks on the same transaction IDs but in different orders, leading to a circular wait condition.

Key changes made to the auto_match_for_account method:

1. Added consistent transaction ID ordering:

   • Before: The inflow/outflow assignment was based solely on amount signs
   • After: First sorts transaction IDs numerically, then adjusts based on amount direction
   • This ensures all processes attempt to acquire locks in the same order

2. Modified the transaction ID assignment logic:

   • Uses array sorting to guarantee consistent ordering ([t1_id, t2_id].sort)
   • Then applies amount-based direction adjustment
   • This prevents the scenario where Process A tries to lock (1,2) while Process B tries to lock (2,1)

3. Maintains existing business logic:

   • Still preserves the amount-based directionality (positive amounts = outflow)
   • Keeps the same matching criteria (amount, currency, date range)
   • Retains duplicate prevention logic

Added comprehensive test coverage:

• Tests concurrent execution with multiple threads
• Verifies correct transfer creation
• Ensures no deadlocks occur
• Validates proper transaction ID assignment

The original intent of the code was to match transfers based on opposing amounts within a date range, but it didn't account for concurrent execution patterns. The updated version maintains this functionality while adding thread-safety through consistent lock ordering.

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