Session system prompt injects UTC timestamp — model announces wrong local time for UTC+8 users

Summary

The session system prompt contains a line like:

The current date and time in ISO format is 2026-08-25T14:56:54.235Z.

This is UTC (Z suffix). In China (UTC+8) the model reads this value and announces times that are 8 hours off — e.g. telling the user "it is now 05:41, pre-market" when local time is 13:41.

Why this bites Windows users hardest

• On macOS/Linux, date and the TZ database usually agree with the user's locale, so the model can self-correct by checking the environment.
• On Windows + Git Bash there is no zoneinfo database, so TZ="Asia/Shanghai" date silently falls back to UTC — the model's most natural cross-check returns the same wrong answer, reinforcing the error.

Suggestion

Inject the user's local time with an explicit offset (e.g. 2026-08-28T13:41:00+08:00) instead of, or in addition to, the UTC timestamp. Alternatively state explicitly in the prompt that the timestamp is UTC and local conversion is required.

Impact

Any workflow where the model reports the current time (trading sessions, scheduling, reminders) silently produces wrong times for all non-UTC users. For a non-technical user this reads as "the product's clock is broken".

Search the session system-prompt construction and timestamp-generation entry points for the UTC ISO timestamp shown in the issue. Check existing tests and reproduce the behavior on Windows/Git Bash if available. Done means the prompt preserves an unambiguous UTC/local-time interpretation or includes the user's explicit offset, with coverage for non-UTC users.