What triggers it. Disconnected clusters left behind after remove_edge/remove_node mutations, or a cycle with no entry edge from the main flow.

How to fix it. Connect the node into the flow with add_edge from a reachable node, or delete it with remove_node if it is leftover.

Minimal reproducer

This source triggers UNREACHABLE_NODE — checked at build time against the same engine the editor runs.

flowchart LR
  A[Start] --> B[Done]
  C[Orphan] --> D[Cycle]
  D --> C

Open this reproducer in the editor

Run am verify diagram.mmd --json, inspect this code, and apply the smallest source or typed mutation that clears it. If it persists after two mechanical attempts, return the warning and ask for human review.

In the cloned repo, am is bun run bin/am.ts.

Machine-readable: this page as Markdown.

Back to all warning codes, or open a blank editor to try a fix.