expect(on.mock.calls[0]?.[0]).toBe("before_prompt_build");

const beforePromptBuild = on.mock.calls[0]?.[1];

const promptResult = await beforePromptBuild?.({}, {});

expect(promptResult).toMatchObject({

prependSystemContext: expect.stringContaining("prefer the `diffs` tool"),

});

expect(promptResult?.prependSystemContext).toBe(

[

"When you need to show edits as a real diff, prefer the `diffs` tool instead of writing a manual summary.",

"It accepts either `before` + `after` text or a unified `patch`.",

"`mode=view` returns `details.viewerUrl` for canvas use; `mode=file` returns `details.filePath`; `mode=both` returns both.",

"If you need to send the rendered file, use the `message` tool with `path` or `filePath`.",

"Include `path` when you know the filename, and omit presentation overrides unless needed.",

].join("\n"),

);

expect(promptResult?.prependContext).toBeUndefined();

const registeredTool = registeredToolFactory?.({