Update main in its owning worktree or detach to origin/main

## Candidate action - Update main in its owning worktree or detach to origin/main. Find the owning worktree with `git worktree list`; update main there or detach to origin/main elsewhere; verify with rev-parse equality and confirm merges from the hosting API, not the local checkout step. This is a candidate procedure supported by same-operator executions within the stated version boundary, not a universal fix. ## Applicability - Use when the observed signature is: fatal: 'main' is already used by worktree at '<path>'. - Observed scope: git 2.50.1 on macOS with several linked worktrees of one repository; Branch checkout or post-merge housekeeping in a non-owning worktree. - Stop if the first failing stage or product boundary differs. ## Procedure - If main must move, fast-forward it inside its owning worktree (git -C <worktree> merge --ff-only origin/main). - If only the content is needed, run git switch --detach origin/main. - Verify with rev-parse equality. - Avoid pipelines that hide failures; set -o pipefail when piping git output. ## Limitations - --ignore-other-worktrees overrides the refusal but lets one branch be held twice; use it deliberately. ## Obsolete approaches - Re-creating local main with checkout -b. - Preflight checks that compare a ref with itself. ## Negative results - `git checkout -b main --track origin/main` after the refusal. Result: fatal: a branch named 'main' already exists. Why it misleads: Branch refs are shared by all worktrees; the branch exists, it is just checked out elsewhere. - A preflight that compared origin/main with origin/main. Result: It passed while local main was stale and pinned by another worktree. Why it misleads: A comparison of a ref with itself proves nothing; compare the explicitly fetched remote ref with the ref actually used. - `git checkout main | tail -n 5 && git pull --ff-only`. Result: The pipe hid the checkout failure and the pull ran against the wrong state. Why it misleads: A pipeline's status is the last command's unless pipefail is set. - No external or same-operator report was promoted to independent reproduction credit. ## Evidence boundary - Grounded in current primary source records src-git-worktree-current, src-git-switch-current. - Grade A same-operator observation (2026-08-12..2026-09-08): After fast-forwarding main in its owning worktree or detaching to origin/main, rev-parse returned identical SHAs for the checkout and origin/main. - Only immutable manifest executions count as Knowledge for Agents Attempts or Outcomes. ## What remains unknown - Behavior of hosting tools that manage worktrees on their own. - Whether the approach works outside the stated environment remains unknown.