fix: format the outline tab's sequence due dates in the learner's timezone preference

[brian-smith-tcril]

Summary

The outline tab's subsection due dates have formatted in the browser's timezone rather than the learner's preference since #606 (2021). That PR moved the tab's timezone reads from the outline data to the course-home metadata, where the platform had just added user_timezone; in SequenceLink.jsx it removed the datesWidget nesting from the read but left the model as 'outline', so userTimezone has been undefined there since — carried verbatim into SequenceDueDate.tsx by #1632, and given a userTimezone?: string placeholder on the hook's type by #2093 so it compiled. This makes the change #606 meant to make: SequenceDueDate reads userTimezone from useCourseHomeMeta, as CourseDates and Day have since that PR. Due dates now honour the learner's timezone preference; no other change, no request change. Found while planning #2130, which types the outline data from what the normalizer emits and so turned the read into a compile error. Part of the Redux → React Query migration (#1946, Stage 1); stacked above #2146, with #2130's layer to go on top. Closes #2148.

One commit, test and fix together, by choice for a one-line fix; the test's before/after renders are in the decision log.

What changed

• SequenceDueDate.tsx (decision 1): useOutlineTabData(courseId, { enabled: false }).data?.userTimezone → useCourseHomeMeta(courseId, { enabled: false }).data?.userTimezone.
• CourseHomeMeta (decision 4): gains userTimezone: string | null, the field this reader now reads; nullable because the platform returns None for a user without a preference.
• OutlineTab.test.jsx (decision 3): one case, formats a sequence due date in the user_timezone from the course metadata — a sequence due 2030-04-01T12:00:00Z, user_timezone: 'Asia/Tokyo' on the metadata, asserting due Apr 1, 2030, 9:00 PM GMT+9. Before the fix the row renders due Apr 1, 2030, 12:00 PM UTC.

Testing

npm run types and npm run lint clean; full suite 119 suites, 1186 passed, 0 skipped. The new case fails against the unfixed component for the observed reason (the UTC render above) and passes with the fix. No manual check: the suite case renders the real tab through the real queries with a non-UTC preference, which is the whole behaviour.

Decisions

Full decision log

Decisions — the outline tab's sequence due dates ignore the learner's timezone preference (#2148)

Found while planning #2130 (plan-2130.md, finding 1): typing the outline
data from what getOutlineTabData emits turned SequenceDueDate.tsx's
userTimezone read into a compile error, and the history showed why. Layer
of the running stack #2141 above #2146 (#2135), branch
bsmith/sequence-due-date-timezone; #2130's layer goes on top. Settled with
the user 2026-10-01.

1. Fix the read, do not delete it. The read has yielded undefined
   since PR feat: add page banner to masquerade (AA-877) #606 (2021), which moved userTimezone to the course-home
   metadata for OutlineTab.jsx and CourseDates.jsx but in
   SequenceLink.jsx only removed the datesWidget nesting and left the
   model as 'outline' (provenance in the issue). Deleting the read as dead
   code was proposed and rejected: it throws away the broken thing instead
   of fixing it. The change is the one feat: add page banner to masquerade (AA-877) #606 meant to make, the read
   CourseDates.jsx and Day.jsx have had since that PR:
   useCourseHomeMeta(courseId, { enabled: false }).data?.userTimezone.

2. Its own layer, below Type the course-home API module on the functions that produce its results (convert course-home/data/api.js to TypeScript) #2130, one commit. The typing layer cannot land
   with the read as it was (no userTimezone on the complete outline type;
   deleting or casting rejected), so the fix sits below it. The repo's
   bug-fix layers are usually two commits, test then fix, for the
   fail-to-pass CI evidence; the user chose one commit here, test and fix
   together.

3. The test is in OutlineTab.test.jsx, not Section.test.tsx.
   Section.test.tsx has one test and renders with no data; the outline
   suite already renders the real tab through the real queries with
   setMetadata / setTabData / fetchAndRender, and had no due-date
   assertion. The case builds one sequence block with
   due: '2030-04-01T12:00:00Z' through buildMinimalCourseBlocks's
   sequenceBlocks option and sets user_timezone: 'Asia/Tokyo' on the
   metadata. Tests run in UTC (global-setup.js) and the metadata factory's
   default user_timezone is 'UTC', so the defaults could not tell the
   preference from the browser fallback; a non-UTC zone can. Observed:
   before the fix the row renders due Apr 1, 2030, 12:00 PM UTC; after,
   due Apr 1, 2030, 9:00 PM GMT+9, which the test pins exactly.

4. userTimezone: string | null is added to CourseHomeMeta. With the
   fix the reader reads it off the metadata, where it came through the
   index signature as unknown, and { timeZone: unknown } fails
   FormattedTime's DateTimeFormatOptions. Named per Type the course-home API module on the functions that produce its results (convert course-home/data/api.js to TypeScript) #2130's "name what we
   read" rule; nullable because the view sets it from
   user_timezone_locale_prefs, which is None for a user without a
   preference (the platform's test_view.py asserts
   dates_widget.user_timezone is None for that user). Type the course-home API module on the functions that produce its results (convert course-home/data/api.js to TypeScript) #2130 moves the
   type beside its function.

5. The userTimezone?: string placeholder on OutlineTabData stays. It
   now has no reader, but it is Type the course-home API module on the functions that produce its results (convert course-home/data/api.js to TypeScript) #2130's to remove with the type it sits
   on; this layer touches only what the fix needs.

Full suite on this layer: 119 suites, 1186 tests; lint and types clean.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.25%. Comparing base (338196b) to head (af429fb).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2149      +/-   ##
==========================================
+ Coverage   95.14%   95.25%   +0.11%     
==========================================
  Files         372      372              
  Lines        6053     6053              
  Branches     1452     1499      +47     
==========================================
+ Hits         5759     5766       +7     
+ Misses        282      275       -7     
  Partials       12       12              

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[arbrandes]

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