fix(timezone): consolidate table wall-clock conversion

[j15z]

Summary

Date and Expiration cells now share one wall-clock conversion path, so workspace and browser timezone changes cannot silently shift the stored instant. Invalid calendar rollovers are rejected. Nonexistent spring-forward wall times keep the existing scheduled-task and reporting behavior: they move forward by the DST gap, so 2:30 AM in New York becomes the real 3:30 AM instant.

Expiration uses the later instant when a fall-back wall time occurs twice, while ordinary Date cells preserve their earlier-instant behavior. This asymmetry prevents a row from being deleted before the local time the user selected.

This is PR 3 of 4 in the row-expiration stack. It builds on the feature and global flag in PR #7071; PR #7161 adds row-delete triggers above it.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation
• Other: ___________

Testing

• The 170-test timezone/date/Expiration matrix passes under UTC, America/Los_Angeles, America/New_York, and Asia/Tokyo process timezones.
• Coverage includes New York, Berlin, and Lord Howe gaps and folds; Kathmandu and Lord Howe fractional-hour offsets; workspace timezone changes; browser fallback; localized input; invalid dates; and epoch round trips.
• The latest focused timezone, date, import, and inline-editor suites pass 166 tests after the stack was restacked.
• bun run lint:check, bun run type-check, and all 33 repository audits pass.
• Review focus: Expiration must choose the safe later instant for ambiguous times without changing existing Date semantics.

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

Screenshots/Videos

No screenshots captured. Component tests cover the timezone-loading state and verify that editing waits for the resolved workspace or browser timezone.

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Project	Deployment	Actions	Updated (UTC)
docs	Ready	Preview	Aug 28, 2026 11:03pm

[greptile-apps]

Greptile Summary

The PR consolidates table wall-clock conversion and timezone formatting into the shared timezone utility, while tightening date validation and expanding timezone-focused tests.

• Adds shared instant formatting, offset formatting, wall-clock extraction, and DST resolution.
• Routes table date and TTL normalization through the shared resolver.
• Adds coverage for fractional-hour offsets, DST gaps and overlaps, invalid calendar values, and timezone round trips.

Confidence Score: 4/5

The PR should not merge until ambiguous fall-back table inputs preserve the established later-occurrence behavior or the compatibility change is explicitly handled.

The new shared resolver is reached by current date and TTL editor paths and changes a previously accepted ambiguous wall clock to an instant one hour earlier, which can alter persisted dates and expiration epochs.

Files Needing Attention: apps/sim/lib/core/utils/timezone.ts, apps/sim/lib/table/dates.ts

Important Files Changed

Filename	Overview
apps/sim/lib/core/utils/timezone.ts	Introduces the shared formatting and wall-clock resolver, but changes ambiguous fall-back inputs from the later occurrence to the earlier one.
apps/sim/lib/table/dates.ts	Centralizes timezone-aware normalization and adds strict calendar/time validation; it exposes table inputs to the resolver’s ambiguity-policy change.
apps/sim/lib/table/column-types/ttl.ts	Redirects TTL formatting through the shared timezone utility while retaining normalization through the table date path.
apps/sim/lib/core/utils/timezone.test.ts	Adds broad offset and DST coverage, including assertions that codify the changed fall-back ambiguity policy.
apps/sim/lib/table/dates.test.ts	Adds targeted coverage for localized inputs, invalid dates and times, DST transitions, and non-hour offsets.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  Input[Naive table date or TTL input] --> Normalize[normalizeDateCellValue]
  Normalize --> Stamp[zonedWallClockWithOffset]
  Stamp --> Resolve[resolveZonedWallClock]
  Resolve --> Candidate{Ambiguous DST overlap?}
  Candidate -->|No| Instant[Resolved instant]
  Candidate -->|Yes| Earlier[Select earliest exact candidate]
  Earlier --> Persist[Persist date or TTL epoch]

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_{Reviews (1): Last reviewed commit: 65d49f5 | Re-trigger Greptile}

[cubic-dev-ai]

All reported issues were addressed across 7 files

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