fix(web): keep timestamp tooltip dates in English

[Lucenx9]

What Changed

Message timestamp tooltips mix an English ordinal with a localized month, for example 4th giugno 2026 in an Italian browser. Pin the month formatter to en-US so it matches the rest of the date label.

Why

The existing comment explicitly calls for an English tooltip date. This one-line fix implements that intent without changing clock preferences, numeric dates, or other timestamp helpers. Regression tests cover German and Italian runtime locales.

flowchart LR
    A[Message timestamp] --> B[Time using existing locale and clock preference]
    A --> C[English ordinal day and year]
    A --> D[Month formatted in en-US]
    B --> E[Chat timestamp tooltip]
    C --> E
    D --> E

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UI Changes

Same seeded conversation in the running web app, Chromium with it-IT locale and Europe/Rome timezone. Both images are cropped PNGs at 2× density. Before uses the unchanged formatter from eee05575eb; after uses this fix. Verified both user and assistant message tooltips. No mobile or packaged desktop run.

Before:

After:

Verification

• vp test run src/timestampFormat.test.ts --project unit --maxWorkers 1 in apps/web: 25 passed. Both new regression cases failed before the fix.
• Targeted lint, formatting, and typecheck of the changed files: passed.
• Full web-package typecheck is blocked by TS2554 in unchanged src/components/files/fileEditorVirtualization.test.ts:260, which passes four arguments to a method accepting at most three. No diagnostics were suppressed.
• Fallow audit against eee05575eb, scoped to web with one thread: passed with no introduced findings.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes. Not applicable, only tooltip text changes.

Model: GPT-5. Harness: Codex in T3 Code.

Note

Force English locale for monthNameFormatter in timestamp tooltips

Sets the module-level month formatter in timestampFormat.ts to en-US instead of the runtime default locale. Adds tests in timestampFormat.test.ts that mock German and Italian runtime locales and confirm the tooltip output stays in English.

^{Macroscope summarized 1ff911d.}

Summary by CodeRabbit

• Bug Fixes
  • Chat timestamp tooltips now consistently display month names in English, regardless of the device or browser locale.
  • Added coverage to verify consistent English formatting across German and Italian locales.

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[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-06T02:04:07.315421Z	1ff911d	PR opened

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[macroscopeapp]

Approvability

Verdict: Approved at 1ff911d

Macroscope's review found this PR approvable — This is a narrowly scoped timestamp-tooltip fix that explicitly formats the existing English date label in English, with regression coverage for non-English runtimes. It does not alter user-configurable timestamp defaults or introduce broader runtime behavior.

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📥 Commits

Reviewing files that changed from the base of the PR and between eee0557 and 1ff911d.

📒 Files selected for processing (2)

• apps/web/src/timestampFormat.test.ts
• apps/web/src/timestampFormat.ts

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📝 Walkthrough

Walkthrough

The chat timestamp formatter now uses the en-US locale for month names. Tests verify English tooltip labels when the runtime locale is German or Italian.

Changes

Timestamp tooltip locale

Layer / File(s)	Summary
English month formatting and locale coverage apps/web/src/timestampFormat.ts, apps/web/src/timestampFormat.test.ts	monthNameFormatter now uses en-US. Tests mock German and Italian runtime locales and verify the English tooltip date label.

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

Merge Risk: ⚪ Minimal · up to 1ff91

Chat timestamp tooltips now consistently use English month names while retaining existing time and numeric-date preferences. The focused locale coverage indicates the change is ready to merge.

Suggested reviewers: juliusmarminge, t3dotgg

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 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 and concisely identifies the main change: keeping web timestamp tooltip dates in English.
Description check	✅ Passed	The description includes the required sections, explains the change and rationale, documents UI changes with before and after screenshots, and reports verification results and the unrelated typecheck …
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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