Design the TaskFlow Error Envelope statusCode, code, message, details, requestId, timestamp, and path
Phase 13 - Professional Error Handling Volume 04 - Professional Backend
Architecture milestone failure
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normalized API error
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client + support correlation
Phase 13 creates one professional exception boundary and a correlation story that spans client response and server logs.
Design the TaskFlow error envelope The API now needs a format that is useful to browser code, PowerShell tests, future mobile clients, and production logs. Keep it small. Every field should answer a real debugging or client-handling question.
export type ApiErrorDetails = string[] | Record<string, unknown>;export type ApiErrorResponse = { statusCode: number; code: string; message: string; requestId: string; timestamp: string; path: string; details?: ApiErrorDetails; };
Examples by failure type // 400 validation { "statusCode": 400, "code": "BAD_REQUEST", "message": "Request validation failed.", "details": ["title: String must contain at least 1 character(s)"], "requestId": "12", "timestamp": "...", "path": "/tasks" }
// 404 domain failure { "statusCode": 404, "code": "TASK_NOT_FOUND", "message": "Task 123... was not found.", "requestId": "13", "timestamp": "...", "path": "/tasks/123..." }
// 500 unexpected fault { "statusCode": 500, "code": "INTERNAL_ERROR", "message": "An unexpected server error occurred.", "requestId": "14", "timestamp": "...", "path": "/tasks" }
Why requestId belongs in the client response When a user reports a failure, “it broke at 2:13 AM” is weak evidence. A request identifier gives support and engineering teams an exact correlation key that can be searched in server logs.
Figure 1 - Correlation workflow Client receives requestId = 14
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A correlation identifier connects a sanitized public response to private server diagnostics without exposing those diagnostics.
Do not overstuff the contract Avoid sending implementation fields such as Prisma stack, database host, migration name, SQL statement, source file path, or environment variable values. They belong in protected logs, not the public transport contract.
Authentication answers who the request represents. Treating decoded or client-supplied identity as trusted is a security boundary failure.
Restate the goal of “Design the TaskFlow Error Envelope” as one observable behavior. Write the success signal before touching code.
Trace the boundary map: credentials/session → token → verification → trusted identity → protected operation. Mark the one boundary this lesson changes.
Inspect the current repository state and record the exact files, route, table, or runtime involved. Avoid creating an abstraction before you can name the existing owner.
Implement the smallest vertical slice. Add one coherent change, run the narrowest verification command, and read the output before continuing.
Connect the slice to TaskFlow’s phase artifact: Error taxonomy + NestJS mapping layer/filters + structured error response with request IDs.. Verify behavior from the outside as a user or API client would.
Create one controlled failure that is safe to reproduce. Predict the symptom first, capture evidence, locate the earliest broken boundary, then fix only that cause.
Close the reference and rebuild or explain the core change from memory. Record what you would monitor or test before trusting the same change in production.
const token = readBearerToken(request);
const claims = await verifier.verify(token);
request.user = {
id: claims.sub,
email: claims.email,
};Do not copy this as a finished answer. Predict what each boundary does, type the smallest useful slice, run it, then compare the result with your prediction.
Inspect whether a token exists, whether it is expired, which issuer/audience signed it, and what the API verifier expects.
Trust only verified server claims; never repair identity by accepting a client-sent user id.
Without copying the final source, create a second small scenario that applies “Design the TaskFlow Error Envelope” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Map errors to one stable HTTP envelope at a central boundary.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Using one generic 400 for semantically different failures
Predict the symptom before causing the failure. Then locate the earliest boundary where reality diverges from expectation.Why does this responsibility live here, what input does it trust, what output proves success, and what would go wrong if another layer owned it?
If your explanation is vague, repeat the boundary trace before moving on.Close the reference. Reproduce the core idea from memory or explain the exact request/data flow aloud. Then check your diff or notes for accidental shortcuts that bypass validation, authorization, error handling, or verification earned in earlier phases.