fix(tui): fixed audited scrollback tail rows

Separated audited offerable transcript rows from durable snapshot rows so lower finalized content below a live block can be repaired instead of duplicated when the live block grows.

Added transcript and virtual-terminal regressions for the lower finalized tail case.

Fixes #4326

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

@@ -2,6 +2,16 @@ import { describe, expect, it } from "bun:test";
 import { TranscriptContainer } from "@oh-my-pi/pi-coding-agent/modes/components/transcript-container";
 import type { Component } from "@oh-my-pi/pi-tui";
 
+class FinalizedBlock implements Component {
+	#lines: string[];
+	constructor(lines: string[]) {
+		this.#lines = [...lines];
+	}
+	render(width: number): string[] {
+		return this.#lines.map(line => line.slice(0, width));
+	}
+}
+
 class MutableLiveBlock implements Component {
 	#lines: string[];
 	constructor(lines: string[]) {
@@ -34,4 +44,19 @@ describe("transcript streaming commit (assistant text)", () => {
 		// off head must be committable to native scrollback (tmux pane history).
 		expect(chat.getNativeScrollbackCommitSafeEnd()).toBe(3);
 	});
+
+	it("offers lower finalized siblings without making them durable", () => {
+		const chat = new TranscriptContainer();
+		const top = new FinalizedBlock(["top-0"]);
+		const live = new MutableLiveBlock(["live-0"]);
+		const tail = new FinalizedBlock(["tail-0", "tail-1"]);
+		chat.addChild(top);
+		chat.addChild(live);
+		chat.addChild(tail);
+
+		expect(chat.render(80)).toEqual(["top-0", "", "live-0", "", "tail-0", "tail-1"]);
+		expect(chat.getNativeScrollbackLiveRegionStart()).toBe(2);
+		expect(chat.getNativeScrollbackSnapshotSafeEnd()).toBe(3);
+		expect(chat.getNativeScrollbackOfferSafeEnd()).toBe(6);
+	});
 });