oh-my-pi/packages/coding-agent/test/transcript-streaming-commit-repro.test.ts

import { describe, expect, it } from "bun:test";
import { TranscriptContainer } from "@oh-my-pi/pi-coding-agent/modes/components/transcript-container";
import { type Component, TERMINAL } from "@oh-my-pi/pi-tui";

type MutableTerminalInfo = { eagerEraseScrollbackRisk: boolean };
const mutableTerminalInfo = TERMINAL as unknown as MutableTerminalInfo;

async function withTerminalRisk<T>(risk: boolean, run: () => T | Promise<T>): Promise<T> {
	const saved = TERMINAL.eagerEraseScrollbackRisk;
	mutableTerminalInfo.eagerEraseScrollbackRisk = risk;
	try {
		return await run();
	} finally {
		mutableTerminalInfo.eagerEraseScrollbackRisk = saved;
	}
}

class MutableLiveBlock implements Component {
	#lines: string[];
	constructor(lines: string[]) {
		this.#lines = [...lines];
	}
	render(width: number): string[] {
		return this.#lines.map(line => line.slice(0, width));
	}
	setLines(lines: string[]): void {
		this.#lines = [...lines];
	}
	isTranscriptBlockFinalized(): boolean {
		return false;
	}
}

describe("transcript streaming commit (assistant text)", () => {
	it("treats in-place growth of the trailing line as append-only", async () => {
		await withTerminalRisk(true, () => {
			const chat = new TranscriptContainer();
			// Models a streaming assistant reply: stable head rows plus a current
			// line that grows token-by-token without adding a new row.
			const block = new MutableLiveBlock(["para one", "para two", "the quick brown"]);
			chat.addChild(block);

			chat.render(80);

			block.setLines(["para one", "para two", "the quick brown fox"]);
			chat.render(80);
			// The head rows never changed; only the trailing line grew. Its scrolled-
			// off head must be committable to native scrollback (tmux pane history).
			expect(chat.getNativeScrollbackCommitSafeEnd()).toBe(3);
		});
	});
});