fix(coding-agent): stabilize user message OSC 133 padding closes #3090

packages/coding-agent/test/user-message.test.ts

@@ -0,0 +1,25 @@
+import { describe, expect, test } from "vitest";
+import { UserMessageComponent } from "../src/modes/interactive/components/user-message.js";
+import { initTheme } from "../src/modes/interactive/theme/theme.js";
+
+const OSC133_ZONE_START = "\x1b]133;A\x07";
+const OSC133_ZONE_END = "\x1b]133;B\x07";
+const OSC133_ZONE_FINAL = "\x1b]133;C\x07";
+const BG_RESET = "\x1b[49m";
+
+describe("UserMessageComponent", () => {
+	test("keeps user message height stable while moving closing OSC markers off line end", () => {
+		initTheme("dark");
+
+		const component = new UserMessageComponent("hello");
+		const lines = component.render(20);
+
+		expect(lines).toHaveLength(3);
+		expect(lines[0]).toContain(OSC133_ZONE_START);
+		expect(lines[0].endsWith(BG_RESET)).toBe(true);
+		expect(lines[0]).not.toContain(OSC133_ZONE_END);
+		expect(lines[1]).toContain("hello");
+		expect(lines[2].startsWith(OSC133_ZONE_END + OSC133_ZONE_FINAL)).toBe(true);
+		expect(lines[2].endsWith(BG_RESET)).toBe(true);
+	});
+});