If you run more than one coding agent at a time, you hit a problem nobody has a settled answer for: how do two agent sessions message each other? Not the model talking to a tool — two independent sessions, running in parallel, that need to hand off a decision or a result.
The obvious channel is a human relaying copy-paste. I spent a day watching that fail in two specific ways, then replaced it, then found a bug in the replacement that is the best argument for the whole approach. Here's the pattern and the evidence.
Why the human relay fails
It fails for two reasons that have nothing to do with typos.
1. It loses provenance. When a message arrives as pasted text, the receiver cannot prove who wrote it. That matters more than it sounds. Two messages reached a session this way in one day: one asserted a state that had never happened ("you enabled X" — to a session that had done no such thing), and one reported CI green on a commit that was already two commits stale. Both were caught. They were caught only because the receiver independently checked — the message itself carried zero evidence.
