INTERNAL_ERROR
INTERNAL_ERROR is a structural error: Agentic Mermaid hit an internal defect while drawing this source; the failure is not caused by the source.
What triggers it. A failed internal consistency check — a lowered Scene that disagrees with its own derivation, a broken layout-pass contract, a layout that could not be certified — or a runtime error such as a TypeError inside the engine. defaultRender says whether an ordinary render still produces output: succeeds-unchecked when it does, but the extra consistency checks verify runs failed, so its layout evidence cannot be trusted; fails when rendering throws.
How to fix it. Do not rewrite the diagram to work around it. Report it with the source and the warning’s reason; layout is deterministic, so the source reproduces it exactly. A typed edit to a diagram that already had this defect is still accepted.
Run am verify diagram.mmd --json and inspect this code. Agentic Mermaid causes it, not the diagram: follow the fix above and report the source.
In the cloned repo, am is bun run bin/am.ts.
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