dmail — message your past self at a checkpoint

dmail is a context-window trick. The agent saves a checkpoint at some point in the run, keeps exploring, and — if it learns something the past self should have known — rewinds to the checkpoint and injects a short message. Everything after the checkpoint is dropped; the message takes its place.

Schema

Arg	Type	Required	Description
action	string	yes	checkpoint or send.
checkpoint_id	integer	for send	Which checkpoint to rewind to.
message	string	for send	The note to inject in place of the dropped turns.

Example invocation

{"action": "checkpoint"}

Returns the new checkpoint id, e.g. Saved checkpoint 3.

{
  "action": "send",
  "checkpoint_id": 3,
  "message": "The bug is in retry.py line 88, not the loop. Skip the loop investigation."
}

Output sample

Rewound to checkpoint 3 (dropped 14 turns). Injected message: 'The bug is in retry.py line 88...'

When to use it

• The agent burned 10 turns ruling out a wrong hypothesis and now knows the real answer. Rather than carry the dead investigation forward (and pay tokens on every subsequent turn), dmail drops it.
• Pairs well with todo — the agent re-derives the next steps from a clean slate.

Notes

• Checkpoints are per-session. They don’t persist across Session.fork() boundaries.
• Compaction will still run if context grows — dmail is targeted; compaction is wholesale.

See also

• todo, think, Compaction.