checkpoint

# Checkpoint - Arcgram logic self-check validator One input: a **diagram** (treated as a spec). One question: **is the flow logic well-formed and coherent?** Returns typed findings; marks, never blocks. Sibling to Reconcile: Checkpoint checks **structure** from the diagram alone; Reconcile checks **values** across diagram + code. Run both -> the diagram is a faithful, current spec. It checks the graph's logic structure - **not** drawing quality (the engine auto-handles overlaps/spacing/routing) and **not** semantic correctness (whether the logic is *right* - a human call). **Red line:** reads only the semantic field values `id`, `f`, `t`, `kind`, `role`, `type` (plus optional `status`, `flag`). Never a coordinate, color, size, or spacing. The judge: am I reading a semantic string, or a rendered visual quantity? ## Findings **Tier A - structural integrity (always on).** Domain-agnostic graph theory. | finding | means | |---|---| | `dangling-edge` | an edge points at an id that is not a node | | `orphan-node` | a node has no edge (chain broken) - except a declared `type:'open'` | | `missing-branch` | a decision (`kind:'diamond'`) lacks its Y or N branch | | `disconnected-island` | a cluster with no edge to the main flow | | `duplicate-id` | a node id used more than once | | `missing-field` | a node has no id, or an edge no `f`/`t` | | `missing-meta-version` | `ARCGRAM_META.version` absent | | `empty-diagram` | no nodes - reported uncovered, never falsely "clean" | **Tie...