feat(tui,coding-agent): configurable fullscreen wheel scrolling with auto acceleration

Adds fullscreenWheelScrollLines ("auto" or 1-100). Auto keeps one line
per event in local macOS terminals and scales with wheel velocity
elsewhere, capped at six lines per event.

closes #9758

packages/tui/test/tui-alt-screen.test.ts

@@ -504,6 +504,31 @@ describe("TuiAltScreen", () => {
 		tui.stop();
 	});
 
+	// #9758: wheel line counts can change at runtime; Alt keeps its multiplier.
+	it("applies runtime wheel line count updates", async () => {
+		const terminal = new VirtualTerminal(20, 4);
+		const tui = new TuiAltScreen(terminal, undefined, undefined, { wheelScrollLines: 3 });
+		const deltas: Array<number | undefined> = [];
+		tui.addChild(
+			new MouseRegion(new Text("wheel target", 0, 0), (event) => {
+				if (event.type !== "wheel") return undefined;
+				deltas.push(event.wheelDelta);
+				return { handled: true };
+			}),
+		);
+		tui.start();
+		try {
+			await terminal.waitForRender();
+			terminal.sendInput("\x1b[<64;1;1M");
+			tui.setWheelScrollLines(2);
+			terminal.sendInput("\x1b[<65;1;1M");
+			terminal.sendInput("\x1b[<72;1;1M");
+			assert.deepStrictEqual(deltas, [-3, 2, -10]);
+		} finally {
+			tui.stop();
+		}
+	});
+
 	it("chains unused wheel delta to an outer scroll view", async () => {
 		const terminal = new VirtualTerminal(20, 4);
 		const tui = new TuiAltScreen(terminal, undefined, undefined, { wheelScrollLines: 3 });

packages/tui/test/wheel-scroll.test.ts

@@ -0,0 +1,47 @@
+import assert from "node:assert";
+import { describe, it } from "node:test";
+import { WheelScrollAccelerator } from "../src/wheel-scroll.ts";
+
+function scroll(accelerator: WheelScrollAccelerator, times: number[], direction: -1 | 1 = 1): number[] {
+	return times.map((time) => accelerator.next(direction, time));
+}
+
+// #9758: fullscreen wheel scrolling was one line per notch on terminals that do not accelerate wheels.
+describe("WheelScrollAccelerator", () => {
+	it("uses fixed line counts regardless of timing", () => {
+		const accelerator = new WheelScrollAccelerator(3, true);
+		assert.deepStrictEqual(scroll(accelerator, [0, 10, 20, 1000]), [3, 3, 3, 3]);
+		accelerator.setLines(0.5);
+		assert.strictEqual(accelerator.next(1, 2000), 1);
+	});
+
+	it("keeps one line per event in auto mode when the terminal already accelerates", () => {
+		const accelerator = new WheelScrollAccelerator("auto", false);
+		assert.deepStrictEqual(scroll(accelerator, [0, 10, 20, 30]), [1, 1, 1, 1]);
+	});
+
+	it("scales auto mode with wheel velocity", () => {
+		const accelerator = new WheelScrollAccelerator("auto", true);
+		assert.deepStrictEqual(scroll(accelerator, [0, 150, 300, 450]), [1, 1, 1, 1]);
+		assert.deepStrictEqual(scroll(accelerator, [1000, 1050, 1100, 1150]), [1, 2, 2, 2]);
+		assert.deepStrictEqual(scroll(accelerator, [2000, 2020, 2040, 2060]), [1, 5, 5, 5]);
+		assert.deepStrictEqual(scroll(accelerator, [3000, 3010, 3020, 3030]), [1, 6, 6, 6]);
+	});
+
+	it("does not accelerate bursts of events for a single notch", () => {
+		const accelerator = new WheelScrollAccelerator("auto", true);
+		assert.deepStrictEqual(scroll(accelerator, [0, 3, 6, 9]), [1, 1, 1, 1]);
+	});
+
+	it("resets acceleration on direction changes and pauses", () => {
+		const accelerator = new WheelScrollAccelerator("auto", true);
+		assert.deepStrictEqual(scroll(accelerator, [0, 20, 40]), [1, 5, 5]);
+		assert.strictEqual(accelerator.next(-1, 60), 1);
+		assert.deepStrictEqual(scroll(accelerator, [500, 520]), [1, 5]);
+	});
+
+	it("carries fractional lines between events", () => {
+		const accelerator = new WheelScrollAccelerator("auto", true);
+		assert.deepStrictEqual(scroll(accelerator, [0, 40, 80, 120, 160]), [1, 2, 3, 2, 3]);
+	});
+});