GHSA-vv65-f55v-xm6g: Grackle has command/argument injection in the git worktree executor that enables RCE on provisioned hosts via an unsanitized task branch name (shell:true)

The default git executor used for all worktree operations spawns git through a shell, and the untrusted task branch name flows into the command unsanitized. A caller able to reach the PowerLine SpawnSession RPC (a malicious or compromised agent acting through the orchestration layer, or any client able to spawn a task) can achieve arbitrary command execution as the PowerLine user on every provisioned environment (SSH host, Docker container, or Codespace), escaping the agent sandbox.

This advisory bundles two related defects in worktree.ts (audit findings F1 and F13).