Two agents, one working directory, and a merge nobody asked for
Parallel agents editing one checkout interleave their changes. Isolation costs disk, not correctness.
git
8 posts
Two agents, one working tree, one disaster
Parallel agents sharing a working tree corrupt each other silently. Worktrees fix it, and cost 4.3 seconds and 364 MB each — not the 200ms the contract claims.
Three repositories, one change, and the order that stops it corrupting
Submodule pointers make commit order load-bearing. Parent first records a SHA nobody else can fetch, and automation can silently revert one.
A hand-typed branch name skips the machinery
A branch name tidier than the generated one silently opts out of every automation that discovers work by parsing it. The naming was the interface all along.
Open it as a draft and let a human merge
A pull request that opens and merges in the same run is a push with extra steps. Draft is the one control that works without depending on permissions.
Refusing the write is cheaper than recovering the work
Untracked files on a protected branch exist in one place, so a later branch switch deletes them with no error and nothing to recover. Refuse at write time.
The submodule pointer you accidentally reverted
Staging everything rolls a submodule pointer backwards, and the diff shows two hashes with no ordering. The one guard it needs is an ancestry test.
A documented workflow nothing could execute
A guard blocked the one step a documented runbook required. The fix was not a weaker guard, it was building the sanctioned command it was asking for.