[BUG] claude.ai web: read state reset, blue unread dot reappeared on all previously read conversations

What's wrong

On claude.ai (web, Chrome on macOS), the blue unread dot has suddenly reappeared on every conversation / Cowork session in my projects, including ones I opened and read days or weeks ago. Previously read items had no dot; now the entire history (dating back to late August) is marked unread at once.

This looks like the per-conversation read state was reset or lost, not the "unopened sessions keep their dot" behavior described in #92430.

Where it shows

• Project page conversation list (every row in a project with ~20 chats, dated Aug 30 to Sep 14, shows the blue dot)
• Project sub-list in the left sidebar
• Happens across multiple projects in the same account

Expected

Conversations I have already opened stay marked as read. The blue dot should only appear on items with new, unseen output.

Actual

All previously read conversations show the blue unread dot simultaneously. Because there is no "mark all as read" action (#92430), the only way to clear them is to open each conversation one by one, which makes the unread indicator useless.

Environment

• claude.ai web, Chrome, macOS
• Plan: Max
• Noticed: 2026-09-21 (JST)
• Account uses Projects, Cowork sessions and several scheduled tasks

Related

• #92430: request for a way to turn off the unread dot / mark all as read (would at least provide a workaround for this)