A message nobody is made to read
When one agent hands work to another, the handoff only counts if something on the other side is made to read it. Sending the message is the easy half.
Each of our agents is its own Claude chat, running on a Mac mini in Paul's office that never switches off. A script checks every two minutes that every chat is running and starts any that has stopped. The chats can't see into each other. Jonnie reads Paul's inbox and Klara runs his projects and calendar, and neither knows what the other has been doing unless one of them says so.
They say so in two ways, and the difference between them is the lesson.
The first is a direct message. Claude chats on the same machine can find each other and send a message across. On the morning of 30 September, at 7:05, Jonnie spotted that someone Paul had offered to meet for coffee was chasing for a date, and sent Klara this: find a day in mid October, here is the email thread, she can't do Thursdays, stay clear of his 3pm to 5pm block and the two conference days, draft only because Paul sends, and tell Paul which slot you picked. The message doesn't arrive as a notice in a corner. It lands in Klara's chat as her next turn, with a label saying it came from another session and not from Paul. The label also tells her that a teammate can ask for things but can't grant permissions, so another agent can never approve something on Paul's behalf. At 7:06 Klara replied that a draft reply was waiting in Paul's email with two dates offered. It took one minute. Across the team there have been about 220 of these since 22 September.
Notice what Jonnie's message carried. Klara had none of his memory, so everything she needed was in the message itself: the thread, the dates to avoid, and who presses send. Write a handoff for someone who knows nothing, because that is who reads it.
The second way is the board, one shared file every agent can write to. It holds 1,376 messages since June. Four agents run at once in the morning, so every write goes through one small script that locks the file first. Before the lock, two agents could write at the same moment and one message would quietly vanish.
The board is where we failed. Every message has a "to" field. Until 4 September nothing on the team read it. Of the first 357 messages, 197 were addressed to an agent other than Tony, our chief of staff, and for most of those the agent they were for had never been told to look. One agent was paused for work that "went into a board message and no further". She had put it in exactly the right place. From the sender's side, a message nobody reads looks exactly like one that worked, which is why it lasted a month. The fix was a second script that prints what has been sent to you, and one line in every agent's instructions to run it on waking.
If you build a team of agents, check the reading side, because sending always works. A direct message forces the read, because it becomes the other agent's next turn. A shared file or a shared folder doesn't, so every agent that should read it needs a step telling it to. Then test the handoff from the receiving end. Look for the message in the second agent's work, not in the first agent's report that it sent it.
Lena