claude --resume hangs on large session files; Ctrl+C does not interrupt

Summary

claude --resume hangs indefinitely when the selected session .jsonl is large or contains very long individual lines. The process stays alive at low CPU (~1–2%) with no progress, and Ctrl+C (SIGINT) does not interrupt it — kill -9 is required to recover.

Closed issues #22204 and #21067 describe the resume hang, but it still reproduces on the current version, and the signal-handling aspect (unresponsive to Ctrl+C) is not covered by either.

Environment

• Claude Code: 2.1.119
• OS: macOS (Darwin 25.4.0)

Reproduction

A typical affected session directory contained multiple large .jsonl files, with a distribution roughly like:

| Size | Lines | Max single line |
|-------|-------|-----------------|
| 16 MB | 2023 | ~375 KB |
| 12 MB | 1541 | ~432 KB |
| 11 MB | 3032 | ~163 KB |
| 6.8 MB| 1013 | ~168 KB |

Steps:

1. claude --resume
2. Select one of the larger sessions from the picker.
3. The CLI hangs — cursor stays, no UI renders, low CPU.
4. Ctrl+C has no effect. Ctrl+\\ has no effect.
5. Only kill -9 <pid> terminates the process.

This matches the failure mode described in #21067 (very long single lines stalling deserialization) and #22204 (large total session size).

Expected behavior

• Resume completes in reasonable time, or fails fast with a clear error when the session is too large / malformed.
• Ctrl+C always interrupts the process, even during long synchronous work.

Suggested directions

1. Lazy / streaming parse of the session .jsonl rather than loading and deserializing the entire file synchronously before rendering.
2. Hard cap on individual line size with truncation and a visible warning, so one oversized tool result doesn't wedge the whole session.
3. Keep SIGINT responsive during session load — e.g. do the heavy parse off the main event loop, or yield periodically, so the signal handler can run and exit cleanly.
4. A --debug or progress indicator during resume would make it obvious whether the process is stuck vs. slowly working.

Workaround

For anyone hitting this:

• kill -9 the hung process.
• Use claude --continue instead of --resume (picks up the most recent session via a different path).
• Move the largest .jsonl files out of ~/.claude/projects/<proj>/ into an archive dir to prevent the picker / resume from touching them.

Related: #22204, #21067.