fix(coding-agent): stabilize OAuth login prompt rows

closes #5433

packages/coding-agent/test/suite/regressions/5433-extension-oauth-prompt-input.test.ts

@@ -0,0 +1,93 @@
+import { setKeybindings, type TUI } from "@earendil-works/pi-tui";
+import { beforeAll, beforeEach, describe, expect, test, vi } from "vitest";
+import { KeybindingsManager } from "../../../src/core/keybindings.ts";
+import { LoginDialogComponent } from "../../../src/modes/interactive/components/login-dialog.ts";
+import { initTheme } from "../../../src/modes/interactive/theme/theme.ts";
+import { stripAnsi } from "../../../src/utils/ansi.ts";
+
+vi.mock("../../../src/utils/open-browser.ts", () => ({
+	openBrowser: vi.fn(),
+}));
+
+function createDialog(): LoginDialogComponent {
+	return new LoginDialogComponent(
+		{ requestRender: vi.fn() } as unknown as TUI,
+		"prompt-repro",
+		() => {},
+		"Prompt Repro",
+	);
+}
+
+function renderDialog(dialog: LoginDialogComponent): string[] {
+	return stripAnsi(dialog.render(120).join("\n"))
+		.split("\n")
+		.map((line) => line.trimEnd());
+}
+
+function countRenderedValue(lines: string[], value: string): number {
+	return lines.filter((line) => line.trim() === `> ${value}`).length;
+}
+
+describe("LoginDialogComponent OAuth prompts", () => {
+	beforeAll(() => {
+		initTheme("dark");
+	});
+
+	beforeEach(() => {
+		setKeybindings(new KeybindingsManager());
+	});
+
+	test("keeps previous prompt input stable when a later prompt is active", async () => {
+		const dialog = createDialog();
+
+		const firstPrompt = dialog.showPrompt("First prompt:", "first-value");
+		dialog.handleInput("first-value");
+		dialog.handleInput("\n");
+		await expect(firstPrompt).resolves.toBe("first-value");
+
+		const secondPrompt = dialog.showPrompt("Second prompt:");
+		dialog.handleInput("second-secret-demo");
+
+		const lines = renderDialog(dialog);
+		expect(lines.join("\n")).toContain("First prompt:");
+		expect(lines.join("\n")).toContain("Second prompt:");
+		expect(countRenderedValue(lines, "first-value")).toBe(1);
+		expect(countRenderedValue(lines, "second-secret-demo")).toBe(1);
+
+		dialog.handleInput("\n");
+		await expect(secondPrompt).resolves.toBe("second-secret-demo");
+	});
+
+	test("preserves auth instructions when showing a prompt", () => {
+		const dialog = createDialog();
+
+		dialog.showAuth("https://example.invalid/login", "Authorize the extension");
+		dialog.showPrompt("First prompt:");
+
+		const output = renderDialog(dialog).join("\n");
+		expect(output).toContain("https://example.invalid/login");
+		expect(output).toContain("Authorize the extension");
+		expect(output).toContain("First prompt:");
+	});
+
+	test("keeps previous manual input stable when a later prompt is active", async () => {
+		const dialog = createDialog();
+
+		const manualInput = dialog.showManualInput("Paste callback URL:");
+		dialog.handleInput("callback-value");
+		dialog.handleInput("\n");
+		await expect(manualInput).resolves.toBe("callback-value");
+
+		const prompt = dialog.showPrompt("Second prompt:");
+		dialog.handleInput("second-secret-demo");
+
+		const lines = renderDialog(dialog);
+		expect(lines.join("\n")).toContain("Paste callback URL:");
+		expect(lines.join("\n")).toContain("Second prompt:");
+		expect(countRenderedValue(lines, "callback-value")).toBe(1);
+		expect(countRenderedValue(lines, "second-secret-demo")).toBe(1);
+
+		dialog.handleInput("\n");
+		await expect(prompt).resolves.toBe("second-secret-demo");
+	});
+});