fix(timezone): consolidate table wall-clock conversion

[j15z]

Summary

TTL and date cells now resolve wall-clock input through one core timezone implementation. This fixes browser/workspace-zone drift, invalid calendar rollover, and direction-dependent DST gap/fold handling while keeping epoch seconds stable when the display timezone changes.

This is the second PR in the stack and builds on PR #7071. It contains the shared conversion consolidation and its regression coverage.

Type of Change

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

Testing

• Ran the 170-test timezone/date/TTL matrix under UTC, America/Los_Angeles, America/New_York, and Asia/Tokyo process timezones.
• Covered New York, Berlin, and Lord Howe DST gaps and folds; Kathmandu and Lord Howe fractional-hour offsets; explicit workspace zones; browser fallback; localized input; invalid dates; and epoch round trips after display-zone changes.
• Ran 273 relevant table, TTL cleanup, cron, import, and UI tests.
• bun run check:api-validation, bun run check, and bunx turbo run lint:check --filter=sim pass.
• Repository-wide TypeScript still reports the existing analytics globals and missing @c15t/scripts modules; it reports no errors in this PR's files.

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

Not applicable. This PR changes shared conversion logic and tests, not UI layout.

Post-Deploy Monitoring & Validation

• Owner and window: Tables on-call for the first 24 hours after deploy.
• Logs: search for Table row TTL cleanup completed and correlate any unexpected deletion reports with the stored TTL epoch and workspace timezone.
• Metrics: watch cron/API success rate, async-job failures, and support/error reports for invalid date or early-expiration behavior.
• Healthy signals: the same TTL epoch renders as the correct local wall time after workspace/browser timezone changes; expired rows delete only after that instant; invalid rollover dates are rejected.
• Failure signals: an epoch changes after display-zone conversion, rows expire early or late near DST transitions, or impossible dates such as February 30 are accepted.
• Mitigation: roll back this PR; if expiration timing is unsafe, also pause the TTL cleanup cron until stored epochs are verified.

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Project	Deployment	Actions	Updated (UTC)
docs	Ready	Preview	Aug 27, 2026 6:27am

[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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