fix(cli): exit cleanly after printing shell completions

Force process termination via `postmortem.quit(0)` in
`Completions.run()` after writing completion scripts to stdout. Loading
all command modules during completion generation leaves open event loop
handles (sockets, timers) that prevent natural process exit, causing
tools like chezmoi to hang.

packages/coding-agent/test/cli-completions-exit.test.ts

@@ -0,0 +1,21 @@
+import { afterEach, describe, expect, it, spyOn } from "bun:test";
+import { postmortem } from "@oh-my-pi/pi-utils";
+import Completions from "../src/commands/completions";
+
+describe("Completions command exit contract", () => {
+	afterEach(() => {
+		spyOn(postmortem, "quit").mockRestore();
+		spyOn(Bun, "write").mockRestore();
+	});
+
+	it("calls postmortem.quit(0) after writing completion script", async () => {
+		const quitSpy = spyOn(postmortem, "quit").mockResolvedValue(undefined);
+		const writeSpy = spyOn(Bun, "write").mockResolvedValue(0);
+		const config = { bin: "omp", version: "0.0.0", commands: new Map() };
+		const cmd = new Completions(["zsh"], config);
+		await cmd.run();
+
+		expect(writeSpy).toHaveBeenCalled();
+		expect(quitSpy).toHaveBeenCalledWith(0);
+	});
+});