Cross-language port (file creation)

Whole-file with `allowCreate` handles new paths. Useful for language ports, scaffolding generators, "explain this and write the test" prompts.

applyEdits with allowCreate: true (the default) handles new files. Pair with the whole-file format and you've got a one-shot scaffolder.

const py = await readFile("src/parser.py", "utf8");
const { text } = await generateText({
  model: openai("gpt-4o"),
  system: WHOLE_FILE_PROMPT,
  prompt: `Port this Python module to Rust. Output as src/parser.rs:\n\n\`\`\`py\n${py}\n\`\`\``,
});
const [r] = await applyEdits(text, async () => null, { formats: ["whole-file"] });
if (r?.ok) await writeFile(r.path, r.after);

Why the file reader returns `null`

The target file (src/parser.rs) doesn't exist yet. Returning null from the file reader tells the applier to treat this as a create. With allowCreate: true (default), the applier accepts it; with allowCreate: false, you get missing-original back.

Creating multiple files in one response

Same pattern — the model emits one fenced block per file:

src/foo.rs
```rs
... contents ...

src/bar.rs

... contents ...


Both files are created. Order in the response = order they're applied.

Cross-language port (file creation)

Why the file reader returns null

Creating multiple files in one response

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Why the file reader returns `null`