Verification
Prove the happy path
- Can compose a shell from reusable patterns
- Can model all UI states
- Can choose server/client boundaries
- Can verify basic accessibility and responsive behavior
Phase 20 · Lesson 16
Mastery Capstone Lab
Learning contract
What you should be able to do after this
- Explain Mastery Capstone Lab without relying on framework buzzwords.
- Connect the lesson to the phase outcome: Build a production application shell and reusable UI states instead of isolated demo components.
- Reproduce the relevant behavior and verify it with evidence.
- Diagnose at least one representative failure instead of guessing.
Figure 20.16 — TaskFlow boundary map
route/layout
server data boundary
page composition
client interaction islands
responsive/accessibility states
Instructor workflow: predict first → implement the smallest slice → run it → inspect evidence → break one assumption → diagnose → explain it back. Do not copy the whole code block before understanding the first failing boundary.
Mastery Capstone Lab
This is the transfer exercise for Phase 20: Production Application UI. The detailed lessons are now closed-book reference material. Your task is to prove that the phase outcome can be reproduced from requirements, repository evidence, and debugging—not by copying a finished implementation.
Target artifact TaskFlow responsive shell with navigation, workspace context, task screens, loading/empty/error states, and accessible interactions.
Acceptance criteria - Write the behavior and constraints before implementation. - Identify the owning layer and every boundary crossed. - Implement the smallest complete vertical slice. - Verify the happy path from outside the implementation. - Demonstrate at least one expected failure path. - Run the phase-relevant quality checks. - Review the diff for accidental duplication, leaked responsibilities, missing validation/authorization, and hidden environment assumptions.
Evidence packet Save the command/request used, expected result, actual result, one failure reproduction, the fix, and a short explanation of why the final responsibility belongs where it does. This packet is more valuable than a screenshot of a green page because it demonstrates repeatable engineering reasoning.
Stretch Change one requirement after the first implementation. Measure which files must change. If a tiny domain change causes unrelated layers to move, use that evidence to discuss coupling before adding another abstraction.
Executable lesson studio · deployment
Now turn the explanation into engineering skill.
A guided lesson proves you can follow. A capstone proves you can transfer the model to a requirement with fewer cues.
By the end, you should be able to
- Build a production application shell and reusable UI states instead of isolated demo components.
- Produce a reproducible evidence packet for success and failure.
- Defend the architecture and identify one improvement without overengineering.
Figure 20.16B — Mental model
route/layout
server data boundary
page composition
client interaction islands
responsive/accessibility states
Code-along sequence
One coherent change at a time
- 01
Design the application shell first: sidebar/topbar/main content/mobile navigation.
- 02
Create reusable primitives for page header, panel/card, empty state, loading skeleton, and error state.
- 03
Build workspace/board/task navigation with active state derived from routing rather than duplicated local state.
- 04
Compose Server and Client Components so interactive islands remain small.
- 05
Test keyboard focus, labels, landmarks, reduced-motion expectations, and narrow widths.
- 06
Exercise all non-happy states by forcing no data, slow data, error, and forbidden responses.
- 07
Run the phase mastery checklist without looking at the provided implementation.
- 08
Perform a short architecture review and document one trade-off you consciously accepted.
txtCapstone evidence packet
Requirement -> implementation diff -> verification -> controlled failure -> diagnosis -> final proofDo 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.
Break it on purpose
Build debugging memory
- Only styling the success state
- Global client component wrapping the whole app
SymptomInvestigation path
You can only continue by copying the reference
Return to the mental model and acceptance criteria. Rebuild one smaller slice from first principles before reopening the source.
Everything seems to work but proof is weak
Choose an external observer: HTTP client, browser, database query, test runner, health endpoint, or deployment log, and capture deterministic evidence.
Closed-reference challenge
Can you transfer the idea?
Extend the phase artifact with one requirement not used in the guided example while preserving the same ownership rules and verification strategy.
Explain-back
Answer these without reopening the solution
- What did you build without a transcript?
- Which boundary caused the most reasoning effort?
- Which failure gave the strongest evidence?
- What shortcut did you deliberately avoid?
- What would you automate before repeating this in a team?
Lesson studio
Turn the reading into skill
Do it
Compose Server and Client Components so interactive islands remain small.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Break it safely
Mobile layout treated as desktop squeezed smaller
Predict the symptom before causing the failure. Then locate the earliest boundary where reality diverges from expectation.Explain it back
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.Exit ticket
Before marking complete
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.