Parallel Coding Agents Only Work When the Handoffs Live in Files

Most multi-agent demos optimize the wrong metric More agents is not a flex. It is a coordination bill. A lot of multi-agent demos still lead with the same number: how many workers ran at once. Four. Eight. A swarm. That is mostly theater if nobody can say what each worker owned, what it changed, and what still needs verification before merge. Parallelism only helps when intent survives the handoff. If the assignment evaporates when the chat window closes, you do not have a workflow. You have several agents improvising in parallel. Chat history is not a coordination layer This is the first thing people get wrong. A big transcript can drag one session through one task. The moment work splits, chat memory stops being a system and starts being a liability. Missing assumptions multiply. Scope drifts. Two agents solve different versions of the same problem and both think they were clear. The fix is boring and effective: write the contract down. That contract does not need to be huge. It just