159: TypeScript - Typed Vertical Slice Checkpoint

Assessment

Convert one task-manager vertical slice from React form through Express route and repository to TypeScript. Keep the public API contract unchanged. Do not solve compiler errors with any or broad assertions.

Required evidence

• strict typecheck passes;
• runtime validation rejects malformed external data;
• two-user ownership tests remain green;
• the client handles loading, success, and safe error states;
• a note names one guarantee types provide and one they cannot provide.

Exit rule

Proceed when the slice is runnable, tested, and explainable. Otherwise return to 109–114 based on the failing boundary.

Review questions

Draw the value flow on paper and mark every point where data changes from unknown to trusted. Circle every assertion and justify it with a runtime check, generated contract, or tested adapter. If an assertion has no evidence, remove it before proceeding.