When propagating errors through promise rejections, catch blocks, or error transformations, always preserve the original error information to maintain debugging context and error traceability. Common anti-patterns include: - Rejecting promises without the original error: `reject()` instead of `reject(error)` - Generic error messages that lose specifics: `"An error occurred"` instead of the actual error - Not handling unknown error types properly when extracting messages **Good practices:** ```typescript // ✅ Pass the original error when rejecting } catch (error) { this.#setTransactionEnded(true, error); reject(error); // Preserve the original error } // ✅ Handle unknown error types safely while preserving info function makeAppErrorResponse(m: Mutation, e: unknown): MutationResponse { return { result: { error: 'app', details: e instanceof Error ? e.message : String(e), // Convert unknown to string } }; } // ✅ Return rejected promises instead of sync throws in async contexts run(): Promise> { return Promise.reject(new Error('AuthQuery cannot be run')); } ``` This practice significantly improves debugging experience by maintaining the full error chain and context, making it easier to trace issues back to their root cause.