Session resume
Resuming the agent's own saved session (for example claude --resume, codex resume). Re-opens a previous session from the transcript the agent saved on that machine.
Verdict
Handy after a crash or a closed terminal on the same laptop; not a way to carry context anywhere else.
Best for
One person picking a session back up on the machine where it ran.
Poor fit
New sandboxes, other machines, teammates and other agents: the saved session is a local file in one tool's format.
Scores
| Criterion | Score | Why |
|---|---|---|
| Survival across sessions | Partial | Survives a restart on the same machine; not a new sandbox or another machine. |
| Cross-tool reach | Weak | Only the agent that saved it can resume it. |
| Multi-agent sharing | Weak | One agent, one session. |
| Retention of reasons | Partial | Keeps the conversation until the session compacts, then only the summary. |
| Scale | Weak | Bounded by the context window; beyond it, it falls back to compaction. |
| Openness | Partial | Usually readable local files, in a format the vendor controls. |
Strengths
- Built in; nothing to set up.
- Brings back the whole session, as it was saved.
Limits
- Lives in a local file, so it is gone with the sandbox or unreachable from another machine.
- Each agent keeps its own format; Codex cannot resume a Claude Code session or the reverse.
- A resumed long session still has to compact when it fills the window.
How it fails
- The sandbox is recycled overnight and the session file goes with it.
- Resuming a session that was already compacted twice brings back the summary, not the conversation.
Cost
Included in the agent.