GTM API / Create mass-action

Commit a previewed plan into a running bulk dispatch. Requires the commit_token from preview_mass_action over EXACTLY these inputs: the server re-derives the HMAC, so an edited plan, a changed scope or a different caller is 422 invalid_commit_token, and a token older than 15 minutes is 422 commit_token_expired. Re-preview in either case. Re-runs the preview validation, inserts the run and its items and starts dispatching. Always asynchronous: the returned sid is the monitoring handle (get_mass_action with include=metrics, get_mass_actions_metrics, or the mass-actions.settled / .paused webhooks). With canary_mode=first_item only item 1 runs until it succeeds; a canary failure pauses the run with paused_reason=canary_failed (retry the item and resume, release the gate, or delete; left for 7 days it settles itself). A sender's spent daily budget pauses the run with limit_reached and hold_till at the budget's reset, and it resumes by itself. A none-scope run starts empty until leads are appended. Contract: - MCP tool create_mass_action, registry package mcp.orchestration/mass_actions, mount orchestration.mass_actions. - Operation create, response envelope create. - Flags: none.