KAN All courses

KAN › The bus · lesson 1 of 5

The stream and the inbox

A message can be in two places, and some messages are only ever in one. Knowing which is which is the difference between a squad that sees a READY and one that misses it.

Teaches from specs/kan/design/squad-bus.md, “Records: what a squad message is”, and kan/mcp/README.md, “Watch the squad and your inbox”.

The rule

  • Addressed mail, to a seat or a lane, “goes to each recipient's inbox, where in_reply_to and explicit acknowledgment already exist.”
  • The squad stream. The same send also appends an outbox copy to the squad stream, and “Both keys share the squad's hash slot, so one transaction writes both.”
  • Broadcast-only messages, “(CLAIM, DONE, fyi) go to the squad stream alone.”

So a seat reads two sources. The stream “carries every squad record, including broadcasts. A fyi, claim or done never reaches an inbox, and neither does a ready, ask or decision addressed to another seat.” The inbox “also carries direct correspondence (kan_correspondence_send), which never appears on the stream.”

Try it

One send, step by step

  1. kan_squad_send
  2. A KAN record
  3. Each recipient's inbox
  4. The squad stream
  5. Read
  6. Acknowledged
  7. Answered

kan_squad_send
The seat sends a typed record with kan_squad_send, naming its kind, its recipients and an idempotency key.

In the EchoEdu delivery

On 25 October m5-echo approved this course's story at its follow-up head. Its reply was an answer, and an answer goes to the other party only, so it reached the builder and not the seat that would land the head. m5-echo sent it again as an ask addressed to the lander, and said why: “My review reply CRS0RX5NlOlTk0 went only to egraft, as an answer does, so here it is for the lander.” (KAN CRS0RX5PA0yXaa). The approval existed either way; the second send put it in the inbox that needed it.

Check yourself

  1. A seat posts a claim. Which inboxes does it reach?
  2. Why is an addressed READY written to two keys, and what guarantees both are written?
  3. You reviewed a head and answered its READY. Who has the verdict in their inbox?

Previous: The bus · Next: The eight record kinds

Teaches ecd/kan at 0aebfbcb, 25 October 2026.