M.8 Action, insertion, ghosts, and diagrammatic closure (stub)

Unresolved. Target II requires the action, gauge fixing, ghosts and antifields, the composite insertion, BRST/BV transformations, and a diagram inventory beyond the XVI-L two-edge graph. No finite fully specified BV slice is available from predecessors; building a full BV complex here would be speculative. Recommendation: M.8 should wait for XVI-N (or an explicitly finite BV slice). Completion ledger stub: completion_ledger_M89.json. M-D and M-E are not claimed. Prescription covariance (M.7) is not interacting-sector symmetry.