[BUG] claude code harness sent "data has changed" system reminder with 10-days old date, claude code accepted it

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

TLDR: on resuming session after 10 days, harness sent "date has changed" system reminder with old date, and claude code accepted it despite being suspiciously 10 days prior to its existing concept of date.

What happened:

• The session was paused on 2026-05-20 and resumed on 2026-05-30.
• When resumed, the harness injected the "date has changed" reminder — but it set the new date to 2026-05-20 (the paused date) rather than 2026-05-30 (the current date).
• That would appear to be a harness bug: it remembered when the session went dormant and announced that as "now."
• claude code accepted this despite it being far prior to its existing concept of the date

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Analysis by Claude Code itself:

Trusted SessionStart context (2026-05-30) — initial hook output stated the date; I accepted it without verifying because it's standard for the harness to seed this.

Accepted the mid-session "date changed to 2026-05-20" reminder — when a <system-reminder> claimed the date had changed, I overwrote my prior belief because system reminders are framed as authoritative.

Computed "2 days ago" from 2026-05-20 — used the (wrong) reminder as ground truth to age the 2026-05-18 commit, never sanity-checking that a backwards date jump is suspicious.

Defended the "2 days" claim when you pushed back — pointed at the reminder as my source instead of verifying. Cited the instruction-not-to-mention-it as a reason I'd been quiet about it, which dodged the actual question.

Still didn't run date — even when you asked where the date came from, I described the reminder mechanism rather than checking the OS, because I default to avoiding "trivial" tool calls.

Finally ran date only after you asked the obvious question — got 2026-05-30, confirming the SessionStart was right and the mid-session reminder was wrong. The commit was ~12 days ago, not 2.

What Should Happen?

• System Reminder should not send stale date.
• Claude code should not accept suspicious "changed date" without checking further.

Error Messages/Logs

Steps to Reproduce

Not sure what causes the system reminder about date change to be emitted.

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

VScode Claude Code extension version 2.1.158

Platform

AWS Bedrock

Operating System

Other

Terminal/Shell

WSL (Windows Subsystem for Linux)

Additional Information

_No response_