Refactor CLI and Twilio modules; add helper tests and comments

src/config/sessions.test.ts

@@ -0,0 +1,20 @@
+import { describe, expect, it } from "vitest";
+
+import { deriveSessionKey } from "./sessions.js";
+
+describe("sessions", () => {
+	it("returns normalized per-sender key", () => {
+		expect(
+			deriveSessionKey("per-sender", { From: "whatsapp:+1555" }),
+		).toBe("+1555");
+	});
+
+	it("falls back to unknown when sender missing", () => {
+		expect(deriveSessionKey("per-sender", {})).toBe("unknown");
+	});
+
+	it("global scope returns global", () => {
+		expect(deriveSessionKey("global", { From: "+1" })).toBe("global");
+	});
+});
+