Fix #628: Infrastructure: Transaction Processing Pipeline Refactor

[SatyamPandey-07]

✅ Key Features Implemented:

State-Aware Transactions: Updated
models/Transaction.js
to include a status state machine (pending, processing, validated, failed) and a comprehensive processingLogs audit trail.
Multi-Stage Asynchronous Pipeline: Refactored
services/transactionService.js
. Transaction creation now instantly saves a "pending" record (Stage 1) and then asynchronously executes heavy processing like rule evaluation, currency conversion, and approvals (Stage 2).
Event-Driven Architecture: Created
services/eventDispatcher.js
to decouple core transaction logic from side effects.
Decoupled Budget Updates: Updated
services/budgetService.js
to observe the pipeline. It now only triggers budget alerts and goal progress updates once a transaction reaches the validated status.
Centralized Validation: Created
middleware/transactionValidator.js
to pull validation logic out of the route layer and into a reusable middleware component.
Data Migration Tool: Built
scripts/transactionMigration.js
to backfill the new status fields for all existing historical transactions.
New Monitoring API:
GET /api/transactions/:id/processing-logs: Allows users (and developers) to see the exact lifecycle and audit trail of any transaction.

closes #628

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🎉 Thanks for the PR, @SatyamPandey-07!

We really appreciate you taking the time to contribute to ExpenseFlow! 💙

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Project	Deployment	Actions	Updated (UTC)
expenseflow	Ready	Preview, Comment	Feb 12, 2026 8:02am