[BUG] bash_progress events not compacted, causing multi-MB transcripts and resume hang #19199

Preflight Checklist

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

What's Wrong?

Preflight Checklist

• I have searched existing issues (related: /resume command consistently crashing after the agent reads too big files, resulting in full unavailability of command and conversation history until fixed #16251, Cannot resume session when context exceeds limit - no way to compact before loading #14472, but distinct root cause)

What's Wrong?

Session transcripts become bloated with bash_progress events from long-running commands, causing session resume to hang.

When a Bash command runs for an extended period, Claude Code records a progress event to the session transcript every second. After a 2-hour session, the transcript reached 31MB
with 85% being progress updates. Attempting to resume causes the UI to hang indefinitely.

Evidence

  $ ls -lh ~/.claude/projects/-workspace/<session-id>.jsonl
  31M

  $ wc -l ~/.claude/projects/-workspace/<session-id>.jsonl
  6204 lines

  $ grep -c '"type":"progress"' ~/.claude/projects/-workspace/<session-id>.jsonl
  5275 lines  # 85% of transcript

Each progress event looks like:

{"type":"progress","data":{"type":"bash_progress","output":"","elapsedTimeSeconds":142,...}}

Relationship to Existing Issues

• Different from /resume command consistently crashing after the agent reads too big files, resulting in full unavailability of command and conversation history until fixed #16251: That's about large single entries (100KB+ Read results). This is about thousands of small (~500 byte) progress events.
• Different from Cannot resume session when context exceeds limit - no way to compact before loading #14472: That's about context token limits. This is about transcript file bloat before even reaching the model.

What Should Happen?

Progress events should not be persisted to the transcript (they're transient UI state), or should be compacted on session end.

Error Messages/Logs

Steps to Reproduce

1. Start a Claude Code session
2. Run a long-running bash command (30+ minutes)
3. Exit and try to resume

Expected: Session resumes normally
Actual: UI hangs while loading the bloated transcript

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

No response

Claude Code Version

2.1.12 (Claude Code)

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Terminal.app (macOS)

Additional Information

I'm running Claude code in the sandboxed environment (Linux Docker on Mac Os X)