Fix #738: Implement Immutable Ledger Architecture & Event-Sourced Tra…

[SatyamPandey-07]

Key Features Implemented:
Event-Sourced Source of Truth: Created

models/FinancialEvent.js
to store every mutation (Created, Updated, Deleted) as an immutable record. Reconstructing a transaction's state now involves replaying its event stream, providing a perfect audit trail.
Cryptographic Chaining Engine: Built

utils/auditHash.js
which implements SHA-256 chaining and HMAC-256 signatures. Each event points to the hash of the previous event, creating a child-to-parent dependency that makes the ledger tamper-evident.
State Reconstruction Brain: Implemented

services/ledgerService.js
to handle the logic of "replaying" events to arrive at the current state. It includes an

auditChain
method that can verify the integrity of thousands of records in milliseconds.
Integrity Guard Middleware: Developed

middleware/integrityGuard.js
to protect mutation routes. It performs a real-time cryptographic verification of the transaction's history before allowing any further changes, blocking access if a breach is detected.
Event-Native Repositories: Refactored

repositories/expenseRepository.js
and

services/transactionService.js
to automatically generate ledger events on every persistent change, ensuring the ledger is never out of sync with the application state.
Forensic Ledger API: Added

routes/ledger.js
providing administrative endpoints to view full event histories and trigger manual state reconstructions for audit purposes.
Reliability Validation: Created

tests/ledgerIntegrity.test.js
to verify the cryptographic chaining logic and ensure that any unauthorized payload modification breaks the hash chain.

closes #738

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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 23, 2026 4:39am