worktree isolation

In a multi-agent coding fleet, running separate rust-analyzer instances for every Git worktree multiplies memory consumption. Here is how an in-memory VFS overlay shares a single analysis database across worktrees, the Salsa concurrency traps we encountered, and our proposal to upstream.

Every agent harness runs the same loop: write a candidate fix into your checkout, run the tests, revert, try the next one. We moved that loop into overlay shadows of the mirrored workspace, mounted at the workspace's own path, and it got faster, not just cleaner.

Two agents on two worktrees of one repository, sharing one analyzer database, answer each other's questions. A benchmark that forks four worktrees and asserts what each should see, and why we stopped trying to share anything writable.

A delegated task is a scope, a worktree and an acceptance command. The worktree is the part we will not trade away, and the reason is whatever the resident agent happens to be doing at the same moment.