mapsplice will fail fast when:
- the target roadmap does not follow the supported phase/step/task grammar
- a fragment starts at the wrong structural level for the requested anchor
- a step appears before the first phase
- a task list appears without a containing step
- unsupported heading structure appears inside the roadmap body
- a valid
Requiresdependency reference cannot be resolved to a roadmap item after the edit
This strictness is intentional. The tool is designed to produce predictable roadmap edits, not to guess what a malformed document might have meant.