feat(dispose): add Symbol.asyncDispose to ConfigClient and ConfigWatcher (#82)

Symbol.dispose fires stop() as fire-and-forget, so callers using
`await using` would not wait for cleanup to complete. Adding
Symbol.asyncDispose lets the runtime await stop() properly.

Also adds esnext.disposable to tsconfig lib so the symbol type is
recognized by the compiler without a target bump.

Closes #51

Co-authored-by: Claude <noreply@anthropic.com>

Author: zeevdr

src/client.ts

@@ -353,6 +353,13 @@ export class ConfigClient {
 		this.close();
 	}
 
+	/**
+	 * Async dispose pattern support — use with `await using`.
+	 */
+	async [Symbol.asyncDispose](): Promise<void> {
+		this.close();
+	}
+
 	// --- Private helpers ---
 
 	private async fetchServerInfo(): Promise<ServerInfo> {

src/watcher.ts

@@ -357,12 +357,19 @@ export class ConfigWatcher {
 	 * Dispose pattern support (TypeScript 5.2+).
 	 *
 	 * Calls stop() synchronously (best-effort). For full cleanup, prefer
-	 * calling `await watcher.stop()` explicitly.
+	 * `await using` or calling `await watcher.stop()` explicitly.
 	 */
 	[Symbol.dispose](): void {
 		void this.stop();
 	}
 
+	/**
+	 * Async dispose pattern support — use with `await using`.
+	 */
+	async [Symbol.asyncDispose](): Promise<void> {
+		await this.stop();
+	}
+
 	private async loadSnapshot(): Promise<void> {
 		const resp = await this.callGetConfig({
 			tenantId: this.tenantId,

test/client.test.ts

@@ -382,6 +382,23 @@ describe("ConfigClient", () => {
 		});
 	});
 
+	describe("Symbol.asyncDispose", () => {
+		it("closes both stubs and resolves", async () => {
+			await client[Symbol.asyncDispose]();
+			expect(configStub.close).toHaveBeenCalledTimes(1);
+			expect(serverStub.close).toHaveBeenCalledTimes(1);
+		});
+
+		it("works with await using", async () => {
+			await (async () => {
+				await using c = client;
+				void c;
+			})();
+			expect(configStub.close).toHaveBeenCalledTimes(1);
+			expect(serverStub.close).toHaveBeenCalledTimes(1);
+		});
+	});
+
 	describe("per-call timeout", () => {
 		it("get() uses per-call timeout over client default", async () => {
 			let capturedDeadline: number | undefined;

test/watcher.test.ts

@@ -484,6 +484,33 @@ describe("ConfigWatcher", () => {
 		});
 	});
 
+	describe("Symbol.asyncDispose", () => {
+		it("awaits stop() before resolving", async () => {
+			const watcher = createWatcher();
+			mockGetConfigSuccess([]);
+			watcher.field("payments.fee", Number, { default: 0.01 });
+
+			await watcher.start();
+			await watcher[Symbol.asyncDispose]();
+
+			expect(mockStream.cancel).toHaveBeenCalledOnce();
+		});
+
+		it("works with await using", async () => {
+			const watcher = createWatcher();
+			mockGetConfigSuccess([]);
+			watcher.field("payments.fee", Number, { default: 0.01 });
+			await watcher.start();
+
+			await (async () => {
+				await using w = watcher;
+				void w;
+			})();
+
+			expect(mockStream.cancel).toHaveBeenCalledOnce();
+		});
+	});
+
 	describe("processing changes", () => {
 		it("updates fields on data events", async () => {
 			const watcher = createWatcher();

tsconfig.json

@@ -3,7 +3,7 @@
     "target": "ES2022",
     "module": "Node16",
     "moduleResolution": "Node16",
-    "lib": ["ES2022"],
+    "lib": ["ES2022", "esnext.disposable"],
     "outDir": "dist",
     "rootDir": "src",
     "declaration": true,