# Part III — The Two-Way Contract

> Open the machinery that keeps a Flow-Like Board, typed AST, and canonical FlowScript synchronized through semantic reconciliation and guarded changes.

- **Document type:** Part overview
- **Canonical HTML:** [https://book.flow-like.com/part-3/](https://book.flow-like.com/part-3/)
- **Markdown alternate:** [https://book.flow-like.com/part-3/index.md](https://book.flow-like.com/part-3/index.md)
- **Book:** FlowBook — The FlowScript Book
- **Edition:** Open edition · 2026
- **Publisher:** Flow-Like
- **Language:** en
- **Topics:** FlowScript internals, Board AST, round-trip editing, semantic reconciliation, visual programming tools
- **LLM index:** [https://book.flow-like.com/llms.txt](https://book.flow-like.com/llms.txt)

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Two editable views are only trustworthy when neither view quietly destroys what the other one
owns. Part III explains the contract that lets a Flow move between its persisted Board, a typed
semantic model, and canonical FlowScript while preserving identity, layout, and runtime meaning.

The current open edition begins this part with the complete round trip: lowering a Board into
`BoardAst`, rendering canonical text, parsing edits, reconciling semantic differences, and applying
atomic Board commands. Later chapters in the first-edition plan will continue with identity
anchors, safe change, language tools, and run evidence; they will become links here only when
substantive chapters are available.

This part is especially useful for developers building editor integrations, reviewers evaluating
AI-authored changes, and architects who need to understand which representation owns which facts.
It also explains why FlowScript is an authoring language over the executable Flow model—not a
parallel runtime with its own hidden semantics.

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## Chapters in this part

- [Chapter 14: Board ⇄ AST ⇄ Text](https://book.flow-like.com/part-3/14-board-ast-text/index.md): Learn how Flow-Like lowers a Board to a typed AST, renders canonical FlowScript, reconciles semantic edits, applies atomic patches, and preserves identity.