FULL_STACK_DEVELOPER_2026_COMPLETE - Phase 06 Hands-On Lab and Phase Exit
Hands-On Lab and Phase Exit Build, break, debug and explain the first complete TaskFlow request path
Phase 06 turns two working applications into one full-stack system.
http://localhost:3000 apps/web http://localhost:4000
Later phases replace in-memory Todos with Prisma + PostgreSQL.
Figure - TaskFlow Phase 06 architecture. The browser sees Next.js on port 3000 while the independent NestJS API listens on port 4000.
FULL_STACK_DEVELOPER_2026_COMPLETE - Phase 06 Hands-On Lab and Phase Exit
Hands-on lab - make TaskFlow genuinely full stack This lab should be completed with two terminals and one browser. Keep the API and frontend independent processes. The goal is not merely to see Todos on screen; the goal is to explain every network hop that made them appear.
Level 1 - Follow 1 Create apps/web/.env.local with API_BASE_URL and NEXT_PUBLIC_API_BASE_URL. 2 Create src/lib/api/todos.ts with Todo, fetchTodos and response.ok handling. 3 Build /todos as an async Server Component that reads API_BASE_URL. 4 Start apps/api on 4000 and apps/web on 3000; verify server-side Todo rendering. 5 Enable NestJS CORS for localhost:3000 and 127.0.0.1:3000. 6 Build /todos-browser with a Client Component that fetches via NEXT_PUBLIC_API_BASE_URL. 7 Use DevTools Network to prove the direct browser request reaches port 4000.
Level 2 - Modify Add a Refresh Todos button to the Client Component. Keep the implementation simple. Disable the button while a refresh is running and clearly separate loading from empty state.
Level 3 - Implement Add a Create demo Todo button that POSTs JSON using createTodo(). After creation, refresh the collection. In DevTools, identify the OPTIONS preflight and the subsequent POST. Explain why GET did not necessarily require the same preflight.
Level 4 - Engineer Assume production will host the frontend at https://app.taskflow.example and the API at https://api.taskflow.example. Write the environment-variable and CORS configuration plan for development, staging and production. Do not use wildcard CORS as a shortcut. Explain which values are public and which must never enter a browser bundle.
Failure drills Break this Expected lesson
Change NEXT_PUBLIC_API_BASE_URL to Trace exact browser Request URL port 4999
Allow only localhost but open Next through Understand exact origin matching 127.0.0.1
Remove response.ok check then call missing See why fetch promise success != HTTP success route
Oral architecture exam ● Where does a Server Component fetch execute? ● Why does a browser Client Component fetch care about CORS?
FULL_STACK_DEVELOPER_2026_COMPLETE - Phase 06 Hands-On Lab and Phase Exit
Phase 06 exit checklist ● [ ] both apps start independently from their own workspace directories. ● [ ] server-side /todos renders data returned by NestJS. ● [ ] browser-side /todos-browser can read the API through CORS. ● [ ] API URLs come from environment configuration, not repeated literals. ● [ ] no secret is stored in NEXT_PUBLIC_* variables. ● [ ] browser POST JSON can be observed with its preflight when applicable. ● [ ] fetch helpers check response.ok. ● [ ] loading, error, empty and success states are distinct. ● [ ] you can use Network + terminal evidence to locate the failing layer. ● [ ] frontend and API production builds still succeed.
The system can finally communicate end to end, but its Todos still disappear when the API restarts. That is now a real, observable persistence problem. Phase 07 teaches PostgreSQL fundamentals before Prisma is allowed to solve it.
Official source notes Primary framework references: Next.js App Router Fetching Data and fetch API documentation; Next.js Environment Variables documentation; NestJS CORS documentation. Browser protocol references: MDN CORS, preflight request, and Fetch API documentation.
The course remains version-locked to the versions established in Phase 00. These sources are used to verify concepts and current API behavior, not to silently upgrade the course midstream.
Hands On Lab and Phase Exit matters because it changes a real boundary in TaskFlow. The goal is to understand the inputs, owner, observable output, and failure modes before adding more abstraction.
Restate the goal of “Hands On Lab and Phase Exit” as one observable behavior. Write the success signal before touching code.
Trace the boundary map: Next.js UI → typed request → NestJS endpoint → service → response state. 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: A typed API client boundary that can call the NestJS health/tasks endpoints from the appropriate Next.js execution context.. 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.
Input -> owner -> transformation -> observable output -> failure evidenceDo 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.
Return to the nearest observable boundary: input, network, process log, database, or rendered UI. Compare actual evidence with the predicted path.
Change one variable at a time and reproduce the original failure after the fix; otherwise you have correlation, not diagnosis.
Without copying the final source, create a second small scenario that applies “Hands On Lab and Phase Exit” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Call an endpoint from a Client Component and observe browser CORS behavior.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Using the browser-only URL from server-to-server code in deployment
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.