fix: normalize timezone-aware usage date labels

[sonwr]

Problem

Some usage entries with timezone-aware timestamps (e.g. ...Z, ...+09:00, ...-08:00) can be labeled under the wrong day key around day/month boundaries.

Root cause

Date key parsing only handled a narrow ISO shape, so timezone-bearing datetime strings were not consistently normalized to YYYY-MM-DD before day-bucket matching.

Fix

• Added support for ISO datetime prefixes (YYYY-MM-DD followed by T, t, or whitespace) in date key extraction.
• Applied the same normalization fix to both Claude and Codex plugins.

Tests

Added regression tests for both plugins covering boundary cases:

• UTC timestamp (Z)
• UTC+9 timestamp
• UTC-8 timestamp

Test command run locally:

• bun run test plugins/claude/plugin.test.js plugins/codex/plugin.test.js
• Result: 102 passed

Impact

More reliable day-label attribution for usage metrics across timezones, especially near day/month boundaries.

Fixes #254

---

Summary by cubic

Fixes wrong day labels for usage entries with timezone-aware timestamps by normalizing date parsing in the Claude and Codex plugins. Daily buckets like Today are now correct across timezones, including at day/month boundaries.

• Bug Fixes
  • Parse ISO datetimes starting with YYYY-MM-DD followed by T/t/space and normalize to YYYY-MM-DD for matching.
  • Apply the same normalization in both plugins.
  • Add regression tests for Z, +09:00, and -08:00 boundary cases.

^{Written for commit 75d2072. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 4 files

[augmentcode]

🤖 Augment PR Summary

Summary: Fixes incorrect day labeling for usage entries whose date values are full ISO datetimes with timezones.

Changes:

• Extended `dayKeyFromUsageDate()` to also extract a `YYYY-MM-DD` prefix when the input is `YYYY-MM-DD` followed by T/t or whitespace (e.g. ...Z, ...+09:00, ...-08:00).
• Applied the same normalization logic in both the Claude and Codex plugins to keep behavior consistent.
• Added regression tests in both plugin test suites covering UTC, UTC+9, and UTC-8 timestamps near day/month boundaries.

Technical Notes: This change avoids falling back to Date.parse() for ISO datetime strings (which can shift the day when converted to local time), ensuring stable day-bucket matching based on the date portion of the input string.

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[augmentcode]

Review completed. No suggestions at this time.

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[davidarny]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep it up!

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[davidarny]

Looks clean, thanks!

[robinebers]

I'd love to see some examples and/or screenshots to visualize this.

@cubic-dev-ai review

[cubic-dev-ai]

I'd love to see some examples and/or screenshots to visualize this.

@cubic-dev-ai review

@robinebers I have started the AI code review. It will take a few minutes to complete.

[cubic-dev-ai]

No issues found across 4 files

[robinebers]

LGTM