fix(coding-agent): terminated process on cancelled startup resume picker

- Force process exit when the startup session picker is cancelled instead of returning.
- Prevent hanging the event loop caused by long-lived startup handles such as theme listeners and timers.
- Add regression test case to verify clean process termination upon picker cancellation.

packages/coding-agent/src/main.ts

@@ -945,6 +945,7 @@ async function buildSessionOptions(
 interface RunRootCommandDependencies {
 	createAgentSession?: typeof createAgentSession;
 	discoverAuthStorage?: typeof discoverAuthStorage;
+	selectSession?: typeof selectSession;
 	runAcpMode?: RunAcpMode;
 	settings?: Settings;
 	forceSetupWizard?: boolean;
@@ -1131,7 +1132,8 @@ export async function runRootCommand(
 	// (see issue #1668).
 	if (typeof parsedArgs.resume === "string" && !sessionManager) {
 		writeStartupNotice(parsedArgs, `${chalk.dim("Resume cancelled: session is in another project.")}\n`);
-		return;
+		stopStartupWatchdog();
+		process.exit(0);
 	}
 
 	// Handle --resume (no value): show session picker
@@ -1147,17 +1149,26 @@ export async function runRootCommand(
 			preloadedAllSessions = await logger.time("SessionManager.listAll", SessionManager.listAll);
 			if (preloadedAllSessions.length === 0) {
 				writeStartupNotice(parsedArgs, `${chalk.dim("No sessions found")}\n`);
-				return;
+				stopStartupWatchdog();
+				process.exit(0);
 			}
 		}
 		pauseStartupWatchdog();
-		const selected = await logger.time("selectSession", selectSession, folderSessions, {
+		const selected = await logger.time("selectSession", deps.selectSession ?? selectSession, folderSessions, {
 			allSessions: preloadedAllSessions,
 		});
 		resumeStartupWatchdog();
 		if (!selected) {
 			writeStartupNotice(parsedArgs, `${chalk.dim("No session selected")}\n`);
-			return;
+			// Quit instead of returning: startup already armed long-lived handles
+			// (theme watcher + SIGWINCH/macOS appearance listeners via initTheme,
+			// settings save timer, model registry) that keep the event loop alive,
+			// so a bare return hangs the process after the picker leaves the alt
+			// screen. No session was built here, so there is nothing to flush. The
+			// in-session `/resume` picker (selector-controller.ts) takes a different
+			// onCancel that just closes the overlay — only this startup path exits.
+			stopStartupWatchdog();
+			process.exit(0);
 		}
 		// Resuming a session from another project: switch the process into that
 		// project's directory and refresh cwd-derived caches before the session is

packages/coding-agent/test/main-resume-cancel-exit.test.ts

@@ -0,0 +1,84 @@
+/**
+ * Regression: cancelling the startup `--resume` session picker (e.g. pressing
+ * Esc) must terminate the process cleanly. Startup arms long-lived handles
+ * (theme/appearance listeners via initTheme, settings save timer, model
+ * registry), so the previous bare `return` left the event loop with live
+ * handles and the process hung after the picker left the alternate screen.
+ *
+ * The fix exits via `process.exit(0)` — matching the `--version`/`--export`
+ * early-exit convention in the same function. Only this startup call site
+ * exits; the in-session `/resume` picker (selector-controller.ts) keeps its own
+ * onCancel that just closes the overlay.
+ */
+import { describe, expect, it, vi } from "bun:test";
+import * as path from "node:path";
+import { parseArgs } from "@oh-my-pi/pi-coding-agent/cli/args";
+import { Settings } from "@oh-my-pi/pi-coding-agent/config/settings";
+import { runRootCommand } from "@oh-my-pi/pi-coding-agent/main";
+import { AuthStorage } from "@oh-my-pi/pi-coding-agent/session/auth-storage";
+import { TempDir } from "@oh-my-pi/pi-utils";
+
+class ProcessExitSignal extends Error {
+	constructor(readonly code: number) {
+		super(`process.exit(${code})`);
+		this.name = "ProcessExitSignal";
+	}
+}
+
+describe("runRootCommand — startup --resume picker cancellation", () => {
+	it("exits cleanly (process.exit 0) when the picker is cancelled instead of returning and hanging", async () => {
+		using tempDir = TempDir.createSync("@omp-resume-cancel-");
+		const sessionDir = tempDir.path();
+		// One valid session so folderSessions is non-empty and the picker (not the
+		// "No sessions found" probe) is the path under test.
+		await Bun.write(
+			path.join(sessionDir, "existing.jsonl"),
+			`${JSON.stringify({ type: "session", id: "existing-session", cwd: sessionDir, timestamp: new Date().toISOString() })}\n`,
+		);
+
+		const authStorage = await AuthStorage.create(path.join(sessionDir, "auth.db"));
+		const settings = Settings.isolated({ "marketplace.autoUpdate": "off" });
+
+		// --print keeps initTheme non-interactive so no global appearance/SIGWINCH
+		// listeners leak into the rest of the suite; the picker branch is gated on
+		// `resume === true`, not on interactivity, so it still runs.
+		const parsed = parseArgs(["--resume", "--print"]);
+		parsed.noExtensions = true;
+		parsed.noSkills = true;
+		parsed.noRules = true;
+		parsed.noTools = true;
+		parsed.noLsp = true;
+		parsed.sessionDir = sessionDir;
+
+		const exitCodes: number[] = [];
+		vi.spyOn(process, "exit").mockImplementation(((code?: number) => {
+			exitCodes.push(code ?? 0);
+			throw new ProcessExitSignal(code ?? 0);
+		}) as typeof process.exit);
+		vi.spyOn(process.stdout, "write").mockImplementation(() => true);
+
+		let pickerCalled = false;
+		let thrown: unknown;
+		try {
+			await runRootCommand(parsed, ["--resume", "--print"], {
+				discoverAuthStorage: async () => authStorage,
+				settings,
+				selectSession: async () => {
+					pickerCalled = true;
+					return null; // user cancelled (Esc)
+				},
+			});
+		} catch (err) {
+			thrown = err;
+		} finally {
+			vi.restoreAllMocks();
+			authStorage.close();
+		}
+
+		expect(pickerCalled).toBe(true);
+		expect(thrown).toBeInstanceOf(ProcessExitSignal);
+		// Exactly one clean exit — proves the cancel branch terminates instead of
+		// falling through to session creation or returning into a hang.
+		expect(exitCodes).toEqual([0]);
+	}, 15_000);
+});