fix: wrong timezone in expenses

[C4illin]

Summary by CodeRabbit

• Bug Fixes
  • Expense dates now display in the local time zone when editing, helping ensure the selected date and time match what was originally entered.
  • Saving an unchanged expense date preserves its original value, avoiding unintended date shifts.

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: 47444e9d-672c-4953-81f6-ff14a08714e1

📥 Commits

Reviewing files that changed from the base of the PR and between 544d242 and ffc458c.

📒 Files selected for processing (1)

• src/routes/group.$id/expense.$expenseId.tsx

🚧 Files skipped from review as they are similar to previous changes (1)

• src/routes/group.$id/expense.$expenseId.tsx

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📝 Walkthrough

Walkthrough

The change adds a formatter for local datetime input values. The expense edit form uses it to display the stored date and preserves the original date string when the submitted value is unchanged.

Changes

Expense date editing

Layer / File(s)	Summary
Format and submit the expense date src/lib/format.ts, src/routes/group.$id/expense.$expenseId.tsx	toLocalDatetimeString returns an empty string for invalid dates and formats valid dates as local YYYY-MM-DDTHH:mm values. The expense edit form uses the formatted value. On submission, it preserves the original date string when the value is unchanged; otherwise, it converts the entered value to ISO. The resulting date is used for currency conversion and the expense update.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to ffc45

The change fixes the timezone shown when editing expenses. No merge-blocking risk is evident from the supplied context.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the expense timezone issue addressed by the changes.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Inline comments:
Review comments at @src/routes/group.$id/expense.$expenseId.tsx:
- Line 51: Update the expense submission logic associated with the `date` field
to preserve `expense.date` when the submitted value matches its local rendering
from `toLocalDatetimeString`. For edited dates, require an explicit offset
choice when the local time is ambiguous before converting it for the update
mutation.

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: e4a949b5-668f-4ed1-b6b5-536ccf491b82

📥 Commits

Reviewing files that changed from the base of the PR and between 2874d6d and 544d242.

📒 Files selected for processing (2)

• src/lib/format.ts
• src/routes/group.$id/expense.$expenseId.tsx

Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 8 remain after this review.