Parallel agents get one worktree each and one owner per file
Two agents editing the same checkout write over each other, and neither reports an error because each one's write succeeded. Cost scales with the number of agents, not with the amount of work, when they trample and redo.
Where it bit
One night, 13 agents, $824. The collisions were the expensive part, not the work. The build-order page on this site was built in its own git worktree because the main checkout had another session's uncommitted edits on the same two files; the merge then cost one deliberate conflict resolution instead of a silent overwrite. In the video pipeline: CapCut overwrote a draft that was written while it was running, so the rule became check the process, then write.
The practice
One worktree per agent. One owner per file, named in the brief. Shared files go through one writer. Any process that also writes the file is checked before you do, with pgrep -x, because ps | grep -q inverts under pipefail and reports the opposite of the truth.
Check it
git worktree list git status --short | wc -l # in a shared checkout, before any agent starts
Get this check as a script you can run tonight
What to do with this
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