Part of #1946 — Redux → React Query migration (Stage 1). Peeled out of #2083 (layer A of the model-store dissolution, #1977), the way #2065 was peeled out of #2014: a structural change first, so the conversion layer's diff stays about the data source.

Goal: convert the two suggested-schedule alerts to TypeScript, so #2083 adds props to a Props interface rather than growing propTypes it is about to replace.

Tasks

• course-home/suggested-schedule-messaging/ShiftDatesAlert.jsx → .tsx
• course-home/suggested-schedule-messaging/UpgradeToShiftDatesAlert.jsx → .tsx
• propTypes + defaultProps → a Props interface with destructuring defaults, the shape UnitButton uses (refactor: de-class UnitButton and convert it to TypeScript #2065).

Not in scope: UpgradeToCompleteAlert.jsx, which #2083 leaves with the same props it has today — only its data source changes — so it stays .jsx until something needs it converted.

Verify: no behavior change; both alerts still read useModel(model, courseId); npm run types, npm run lint and the full suite green.

Findings that shape the task list

• These two components are the ones Read the dates and outline tab data from their queries, not useModel #2083 gives new props. It passes datesBannerInfo and hasEnded down from the tabs instead of having each alert select a model by name, so both prop lists change. Converting first means that layer edits an interface instead of editing propTypes that TypeScript would delete a layer later.
• ShiftDatesAlert needs courseId narrowed, not asserted. It feeds courseId to courseHomeQueryKeys.datesTab/outlineTab and to the reset-deadlines mutation, all of which want string, while useParams() yields string | undefined. Rather than three courseId! assertions, !courseId joins the early return the component already has, which narrows it for the rest of the body including both closures. The repo's existing courseId! uses all sit in apiHooks.ts beside enabled: !!courseId, where the query cannot run with an undefined id — a component-level assertion has nothing backing it.
• That guard is unreachable today, deliberately so. With an undefined courseId, useModel returns {}, so destructuring datesBannerInfo off it throws before the guard is reached. It only becomes reachable after Read the dates and outline tab data from their queries, not useModel #2083 passes that data in as a prop, and even then only off a course route — where it now renders nothing instead of a button that would POST course_key: undefined.
• No test changes. Neither component has its own test file; both are exercised through DatesTab.test.jsx and OutlineTab.test.jsx.