The roadmap shape `mapsplice` expects

mapsplice treats a roadmap as four structural levels:

• Phases are level-2 headings such as ## 8. Phase title.
• Steps are level-3 headings such as ### 8.2. Step title.
• Tasks are Markdown list items whose first paragraph begins with a number such as - [ ] 8.2.3. Task title.
• Addendum sub-tasks are nested task checklist items whose first paragraph begins with a fourth-level number such as - [ ] 8.2.3.1. Sub-task title.

Optional document preamble content may appear before the first numbered phase. Tasks may also contain extra paragraphs or nested bullet lists beneath the first numbered paragraph. Ordinary nested bullets remain task body Markdown; numbered nested checklist items that use the fourth-level form are addendum sub-tasks owned by their parent task.

Anchors on the command line map directly to those levels:

• 8 targets a phase
• 8.2 targets a step
• 8.2.3 targets a task
• 8.2.3.1 targets an addendum sub-task

Fragments supplied to insert and replace must contain one or more sibling items at the same level as the target anchor.