agent-signals

035. A Claude resume keeps the session ID and the transcript file

View as Markdown Open in Claude Open in ChatGPT
Date
2026-10-30
Agents
Claude Code
Measured on
real machine

Measured

2026-10-30, Claude Code 2.1.314 with --model haiku, on Linux (Debian 13, x64), in a private tmux server with a throwaway HOME. The scenario scenarios/claude/plan-and-resume.sh ran one session, stopped it with /exit, and started claude --resume <sessionId> in a new process. It listed the files below ~/.claude/sessions/ and ~/.claude/projects/ at each step, and recorded every hook payload. One run. Measured on: real machine.

What was measured

  1. After /exit, SessionEnd fired with reason: prompt_input_exit. The files <pid>.json and <pid>.<64 hex characters>.key of the first process were gone. The transcript file stayed.
  2. The new process had a new pid and wrote a new <pid>.json and a new .key file. Its sessionId was the same ID as in the first process.
  3. SessionStart fired with source: resume and the same session_id. Its transcript_path was the same file as in the first process.
  4. The new process appended to that transcript file. The file grew at the resume and again after the next prompt. No other transcript file appeared in the project folder.
  5. After the first prompt of the resumed session, the hooks were UserPromptSubmit, Stop, and then SubagentStop with an empty agent_type. The scenario did not start a subagent. The cause of this SubagentStop is not known.
  6. The resumed screen drew the old conversation, and the name of the session (create-note-txt) in the frame of the input box.

Mechanism

A session ID names one transcript file for the whole life of the session, also across processes. A reader that maps a pid to a session (fact 023) must read the pid file again for each new process. The session ID can stay the same while the pid changes.

Incident

None.

Screens

None.

Not measured