fix(frontend): format sidebar date group labels with the user's locale

[gaoanze888]

Problem

The new sidebar's "Recent chats" day-group labels mix a localized month name with hand-assembled English date parts, producing a format that is incorrect for every locale (#13519):

const day = date.getDate();
const month = date.toLocaleDateString(undefined, { month: "long" });
const label = `${day}${ordinalSuffix(day)} ${month}`;   // "26th June"

The month name follows the user's locale, but the day + English ordinal + "day month year" assembly does not. A zh-CN user sees 20th 六月 (correct would be 6月20日); a de-DE user sees 20th Juni (correct: 20. Juni).

This is reproducible on master — the existing unit tests actually fail on machines with a non-English locale (expected '20th 六月' to be '20th June'), because the expectations hardcode English output.

Fix

Format the label with a single Intl.DateTimeFormat(locale, …) options set, per the suggestion in #13519:

• { day: "numeric", month: "long" } for dates in the current year
• adds year: "numeric" for older dates

Result per locale: June 20 / December 1, 2024 (en-US), 20 June (en-GB), 20. Juni (de-DE), 6月20日 / 2024年12月1日 (zh-CN). The custom ordinalSuffix helper is gone — English ordinals can't be expressed via Intl, and keeping them is what made the format locale-invalid.

getDateGroupLabel and groupSessionsByDate now accept an optional locale (defaulting to the user's locale), mirroring formatHeaderDate in home/helpers.ts, which keeps tests deterministic.

Test plan

• Updated RecentChats/helpers.test.ts: expectations pass an explicit "en-US" locale (no longer runner-locale-dependent), plus new assertions for en-GB, de-DE, and zh-CN covering the previously broken mixed format
• pnpm vitest run src/components/layout/AppSidebar/... — 11/11 pass
• pnpm format, pnpm lint, pnpm types — clean
• Verified the 3 pre-existing failures in home/ tests are unrelated (they fail on unmodified master under a non-en-US locale — Intl.NumberFormat currency prefix; same class of issue as this one, out of scope here)

Fixes #13519

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This PR targets the master branch but does not come from dev or a hotfix/* branch.

Automatically setting the base branch to dev.

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📒 Files selected for processing (2)

• autogpt_platform/frontend/src/components/layout/AppSidebar/components/RecentChats/__tests__/helpers.test.ts
• autogpt_platform/frontend/src/components/layout/AppSidebar/components/RecentChats/helpers.ts

🚧 Files skipped from review as they are similar to previous changes (2)

• autogpt_platform/frontend/src/components/layout/AppSidebar/components/RecentChats/helpers.ts
• autogpt_platform/frontend/src/components/layout/AppSidebar/components/RecentChats/tests/helpers.test.ts

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Walkthrough

Recent chat date grouping now uses locale-aware Intl.DateTimeFormat output. Optional locale parameters flow through date-label generation and session grouping. Tests cover English, German, British English, and Chinese formats.

Changes

Recent chat date localization

Layer / File(s)	Summary
Localized date labels and grouping autogpt_platform/frontend/src/components/layout/AppSidebar/components/RecentChats/helpers.ts, autogpt_platform/frontend/src/components/layout/AppSidebar/components/RecentChats/__tests__/helpers.test.ts	getDateGroupLabel uses Intl.DateTimeFormat and omits the year for current-year dates. getDateGroupLabel and groupSessionsByDate accept an optional locale. Tests validate localized labels and grouping behavior.

Priority: ➖ Normal — Impact reflects medium issue severity.

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

Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to 750a1

Recent Chat date labels now use locale-aware formatting with localized test coverage; no merge-blocking risk is identified.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main change: formatting sidebar date-group labels with the user's locale.
Description check	✅ Passed	The description explains the localization problem, the Intl.DateTimeFormat fix, affected APIs, tests, and verification results.
Linked Issues check	✅ Passed	The changes satisfy issue #13519 by replacing hand-assembled date labels with consistent locale-aware formatting and adding locale coverage in tests.
Out of Scope Changes check	✅ Passed	The changes are limited to Recent Chats date-label formatting, related API parameters, and corresponding tests. No unrelated changes are present.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.34%. Comparing base (6dc5fec) to head (750a1a1).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev   #14437   +/-   ##
=======================================
  Coverage   81.34%   81.34%           
=======================================
  Files        3515     3515           
  Lines      263403   263394    -9     
  Branches    24413    24411    -2     
=======================================
- Hits       214278   214271    -7     
+ Misses      43780    43764   -16     
- Partials     5345     5359   +14     

Flag	Coverage Δ
platform-frontend	60.37% <100.00%> (-0.01%)	⬇️
platform-frontend-e2e	28.67% <0.00%> (-0.10%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
Platform Backend	86.35% <ø> (ø)
Platform Frontend	62.74% <100.00%> (-0.01%)	⬇️
AutoGPT Libs	∅ <ø> (∅)
Classic AutoGPT	28.43% <ø> (ø)

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