fix: Critical bug fixes - transaction handling, error standardization, and solver errors

[TheShahnawaaz]

Summary

This PR resolves 3 critical bugs identified through comprehensive code analysis, improving reliability, consistency, and error handling across the backend.

Bugs Fixed

🔴 Bug #6: Missing Database Transaction in getCabDetails (Medium-High)

File: backend/src/controllers/qr.controller.ts:323-467

• Issue: Multiple sequential queries without transaction created data inconsistency window
• Impact: If cab/allocation deleted between queries, response could contain partial/stale data
• Fix: Wrapped all queries in database transaction with proper BEGIN/COMMIT/ROLLBACK
• Benefit: Ensures atomic reads and data consistency

🟡 Bug #9: Missing Error Handling in Solver (Medium)

File: backend/src/controllers/allocation.controller.ts:76-91

• Issue: Infeasible solver solutions threw unhandled errors causing 500 crashes
• Impact: Server crashes instead of graceful error handling
• Fix: Added try-catch around solver with user-friendly 400 error response
• Benefit: Graceful degradation with actionable error message

🟡 Bug #13: Inconsistent Error Response Format (Low-Medium)

Files: 7 files across middleware and routes

• Issue: Mixed error formats: { error: string } vs { success: false, error: string }
• Impact: Frontend error handling becomes fragile and unpredictable
• Fix: Standardized all error responses to { success: false, error: string, ... }
• Benefit: Consistent API contract, easier frontend integration

Files Changed

• backend/src/controllers/allocation.controller.ts - Solver error handling
• backend/src/controllers/qr.controller.ts - Transaction safety
• backend/src/middleware/auth.middleware.ts - Consistent errors
• backend/src/middleware/cron.middleware.ts - Consistent errors
• backend/src/middleware/webhook.middleware.ts - Consistent errors
• backend/src/routes/auth.routes.ts - Consistent errors
• backend/src/routes/webhook.routes.ts - Consistent errors

Statistics

• Files Modified: 7
• Lines Changed: +111 / -27
• Backward Compatible: ✅ Yes

Testing Recommendations

1. Test cab details retrieval during concurrent allocation changes
2. Test allocation algorithm with infeasible configurations
3. Verify frontend error handling with new consistent format
4. Test authentication failures return proper format

Notes

• Bug Add frontend structure documentation and implement routing setup #4 (Webhook body parsing race condition) was already fixed in previous commits using express.raw()
• All changes maintain backward compatibility
• Error response standardization improves developer experience

Checklist

• Code follows project conventions
• All error paths return consistent format
• Database transactions properly handled
• No breaking changes
• Commit message follows conventional commits

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Project	Deployment	Review	Updated (UTC)
cab-management-system	Ready	Preview, Comment	Jan 13, 2026 11:35pm
cab-management-system-b59a	Ready	Preview, Comment	Jan 13, 2026 11:35pm

[Copilot]

Pull request overview

This PR addresses three critical bugs in the backend: missing database transactions in the cab details endpoint, unhandled solver errors causing server crashes, and inconsistent error response formats across the API. The changes improve data consistency, error handling reliability, and API contract predictability.

Changes:

• Added database transaction wrapper to getCabDetails controller for atomic read consistency across multiple queries
• Implemented try-catch error handling for the solver algorithm to gracefully handle infeasible allocation scenarios
• Standardized error responses to { success: false, error: string, ... } format across 5 middleware and route files

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
backend/src/controllers/qr.controller.ts	Added database transaction with BEGIN/COMMIT/ROLLBACK for atomic reads in getCabDetails function
backend/src/controllers/allocation.controller.ts	Added try-catch wrapper around solver with graceful 400 error response for infeasible solutions
backend/src/middleware/auth.middleware.ts	Standardized all error responses to include success: false field
backend/src/middleware/cron.middleware.ts	Standardized all error responses to include success: false field
backend/src/middleware/webhook.middleware.ts	Standardized all error responses to include success: false field
backend/src/routes/auth.routes.ts	Standardized all error responses to include success: false field; minor comment improvement (Validate → Verify)
backend/src/routes/webhook.routes.ts	Standardized all error responses to include success: false field

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[TheShahnawaaz]

@copilot Can we merge it?

[Copilot]

@TheShahnawaaz I've opened a new pull request, #9, to work on those changes. Once the pull request is ready, I'll request review from you.