delegate_task with environmentId launched in the linked project's checkout even when
isolation "worktree" was asked for. A worktree there would branch from a commit this
checkout has and the other may not, so the call is refused before launching, pointing
at t3_thread_launch with a worktree workspaceStrategy.

Recording the task or its cancellation no longer builds the caller's message from the
dispatch error; the cause goes to the log and the caller gets a fixed message.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>