fix: limit selector window height (#11072)

With this PR, we stop  rendering every option.
Instead, we render a centered, clamped window of up to 10 options and
show `(selection/total)` when the list overflows.

This keeps the selected option visible in long extension-provided lists
without changing navigation, keybindings, callbacks, countdowns, or
short-list rendering.

Fixes #6688.

## Merge Danger

**Door:** Two-way

The change is localized to `ExtensionSelectorComponent.updateList()` and
can be reverted without migration or persisted-state concerns.

**Blast Radius:** Low

Only extension selectors with more than 10 options change appearance;
they now render a window and position indicator instead of every option.

---------

Co-authored-by: Pi via openai-codex (gpt-5.6-sol) <noreply@openai-codex>

packages/coding-agent/src/modes/interactive/components/extension-selector.ts

@@ -84,13 +84,27 @@ export class ExtensionSelectorComponent extends Container {
 
 	private updateList(): void {
 		this.listContainer.clear();
-		for (let i = 0; i < this.options.length; i++) {
+
+		const maxVisible = 10;
+		// Center the window on the selection, then clamp it to the list boundaries.
+		const startIndex = Math.max(
+			0,
+			Math.min(this.selectedIndex - Math.floor(maxVisible / 2), this.options.length - maxVisible),
+		);
+		const endIndex = Math.min(startIndex + maxVisible, this.options.length);
+
+		for (let i = startIndex; i < endIndex; i++) {
 			const isSelected = i === this.selectedIndex;
 			const text = isSelected
 				? theme.fg("accent", "→ ") + theme.fg("accent", this.options[i])
 				: `  ${theme.fg("text", this.options[i])}`;
 			this.listContainer.addChild(new Text(text, 1, 0));
 		}
+
+		if (startIndex > 0 || endIndex < this.options.length) {
+			const scrollInfo = theme.fg("muted", `  (${this.selectedIndex + 1}/${this.options.length})`);
+			this.listContainer.addChild(new Text(scrollInfo, 0, 0));
+		}
 	}
 
 	handleInput(keyData: string): void {

packages/coding-agent/test/extension-selector.test.ts

@@ -0,0 +1,82 @@
+import { setKeybindings } from "@earendil-works/pi-tui";
+import { beforeAll, beforeEach, describe, expect, it } from "vitest";
+import { KeybindingsManager } from "../src/core/keybindings.ts";
+import { ExtensionSelectorComponent } from "../src/modes/interactive/components/extension-selector.ts";
+import { initTheme } from "../src/modes/interactive/theme/theme.ts";
+import { stripAnsi } from "../src/utils/ansi.ts";
+
+function render(selector: ExtensionSelectorComponent): string {
+	return stripAnsi(selector.render(80).join("\n"));
+}
+
+function visibleOptions(output: string): string[] {
+	return output
+		.split("\n")
+		.filter((line) => line.includes("option-"))
+		.map((line) => line.trim().replace(/^→ /, ""));
+}
+
+describe("extension selector", () => {
+	beforeAll(() => {
+		initTheme("dark");
+	});
+
+	beforeEach(() => {
+		setKeybindings(new KeybindingsManager());
+	});
+
+	// #6688: long extension selectors must keep the selected option visible.
+	it("windows long option lists around the selection", () => {
+		const options = Array.from({ length: 15 }, (_, index) => `option-${index + 1}`);
+		const selector = new ExtensionSelectorComponent(
+			"Choose",
+			options,
+			() => {},
+			() => {},
+		);
+
+		let output = render(selector);
+		expect(visibleOptions(output)).toEqual(options.slice(0, 10));
+		expect(output).toContain("→ option-1");
+		expect(output).toContain("  (1/15)");
+
+		for (let i = 0; i < 7; i++) selector.handleInput("\x1b[B");
+		output = render(selector);
+		expect(visibleOptions(output)).toEqual(options.slice(2, 12));
+		expect(output).toContain("→ option-8");
+		expect(output).toContain("  (8/15)");
+
+		for (let i = 0; i < 7; i++) selector.handleInput("\x1b[B");
+		output = render(selector);
+		expect(visibleOptions(output)).toEqual(options.slice(5, 15));
+		expect(output).toContain("→ option-15");
+		expect(output).toContain("  (15/15)");
+	});
+
+	it("renders short and empty option lists without a scroll indicator", () => {
+		const shortOptions = ["option-1", "option-2", "option-3"];
+		const shortOutput = render(
+			new ExtensionSelectorComponent(
+				"Choose",
+				shortOptions,
+				() => {},
+				() => {},
+			),
+		);
+		expect(visibleOptions(shortOutput)).toEqual(shortOptions);
+		expect(shortOutput).toContain("→ option-1");
+		expect(shortOutput).not.toContain("(1/3)");
+
+		const emptyOutput = render(
+			new ExtensionSelectorComponent(
+				"Choose",
+				[],
+				() => {},
+				() => {},
+			),
+		);
+		expect(emptyOutput).toContain("Choose");
+		expect(emptyOutput).toContain("↑↓ navigate");
+		expect(emptyOutput).not.toContain("→");
+	});
+});