Why: cmd_start derived the worktree location from $PWD, so running task.sh start from a repository subdirectory (or inside a task worktree) placed the new worktree at the wrong spot — e.g. scripts-wt-<slug> nested inside the repo.
Evidence: bash -n clean; functional smoke of the patched script from both the main checkout scripts/ subdir and the repo root created ../Agent-System-Dev-wt-<slug> as a sibling of the main checkout (paths asserted; pre-fix subdir run would nest inside the repo); git rev-parse --git-common-dir resolves to the main checkout from both locations (relative ../.git vs absolute).
Impact: scripts/task.sh cmd_start only; from the main checkout root the derived path is identical to before; new worktrees now always land as siblings of the main checkout regardless of invocation directory.
Refs: .task/feature-task-start-rootfix.md
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