[BUG] Session not visible in session list; no diagnostics for very large transcripts (165MB+) and bulk-touched mtimes

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?

A user's overnight work session was not visible in the app's session list, and there was no user-facing way to diagnose why.

Investigation (from within another Claude Code session) found:

1. Exhaustive scan of ~/.claude/projects/*/**.jsonl showed no Claude Code transcript active in the window in question (KST Aug 18 21:00 - Aug 19 03:30). The work was eventually traced to a third-party CLI agent session on disk, so no data was lost - but the user had no way to know this from Claude Code itself.
2. Two Claude Code observations made recovery harder:
3. - Transcript files' mtimes across all projects were bulk-updated to the investigation time (apparently touched by the app/indexer), destroying file-time-based forensics.
4. - The current session's transcript has grown past 165 MB and keeps growing. Behavior/limits of the session list and resume for very large transcripts appear undocumented.

What Should Happen?

1) Every locally stored transcript is represented in the session list, or a diagnostic (e.g. a claude doctor section) lets users enumerate/verify local transcripts when one looks missing. 2) Session list and resume keep working for very large transcripts (hundreds of MB), or the app auto-compacts/rotates them and documents the limit. 3) The app/indexer does not rewrite transcript mtimes when merely reading/indexing.

Error Messages/Logs

Steps to Reproduce

Hard to reproduce deterministically; conditions observed on this machine (macOS 26.5.2, Claude Code 2.1.226):

1. Have many long-running sessions across multiple projects; keep one interactive session running for weeks until its transcript exceeds 165 MB.
2. 2. Work overnight in other agent tooling; next day, try to locate that work via the Claude Code session list.
3. 3. Observe: no way from within the app to enumerate/verify local transcripts, and all transcript mtimes under ~/.claude/projects/ get bulk-updated (touched) while the app is running, so file times cannot be used to find "the session from last night".

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.226 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

Environment: Claude Code desktop app (macOS), local-agent mode. Filed on behalf of the account owner from within a Claude Code session. Full bilingual (KR/EN) incident report with timeline and file-level evidence is available on request.