test(tenancy): un-skip reportFirstDmSent POST assertion (#129)

src/tenancy/__tests__/heartbeat.test.ts

@@ -129,16 +129,45 @@ describe("reportAgentReady", () => {
 });
 
 describe("reportFirstDmSent", () => {
-	// FIXME: this test fails on Bun 1.3.13 in CI with `expect(count).toBe(1)`
-	// receiving 0, despite the structurally-identical reportAgentReady
-	// "POSTs to ..." test passing on the same runtime. Two refactors did not
-	// fix it (removing the mock() cast, then switching to a globalThis.fetch
-	// override). The implementation is verified correct on local Bun 1.3.5
-	// (8/8 pass) and the reportAgentReady sibling test exercises the same
-	// postBestEffort path on every CI run. Marked todo to unblock the merge;
-	// tracked in follow-up notes for a Bun 1.3.13 closure-mutation
-	// investigation.
-	test.todo("POSTs to /v1/tenant_status/first_dm_sent with the slack_message_ts", () => {});
+	test("POSTs to /v1/tenant_status/first_dm_sent with the slack_message_ts", async () => {
+		// Mirrors the passing reportAgentReady sibling: override
+		// globalThis.fetch with a plain async function that mutates only
+		// scalar locals. The earlier closure-captured-array recorder was
+		// what surfaced the Bun 1.3.13 `expect(count).toBe(1)` -> 0 flake;
+		// scalar locals + the mandatory try/finally restore avoid it.
+		let count = 0;
+		let lastUrl = "";
+		let lastBody = "";
+		let lastMethod = "";
+		let lastContentType = "";
+
+		const originalFetch = globalThis.fetch;
+		try {
+			globalThis.fetch = (async (input: string | URL | Request, init?: RequestInit) => {
+				count++;
+				lastUrl = typeof input === "string" ? input : input.toString();
+				lastBody = String(init?.body ?? "");
+				lastMethod = String(init?.method ?? "");
+				const headers = init?.headers as Record<string, string> | undefined;
+				lastContentType = headers?.["content-type"] ?? "";
+				return new Response(null, { status: 204 });
+			}) as typeof fetch;
+
+			await reportFirstDmSent({
+				metadataBaseUrl: "http://169.254.169.254",
+				slackMessageTs: "1715000000.000123",
+				// no fetchImpl: exercise the globalThis.fetch fallback path.
+			});
+
+			expect(count).toBe(1);
+			expect(lastUrl).toBe("http://169.254.169.254/v1/tenant_status/first_dm_sent");
+			expect(lastMethod).toBe("POST");
+			expect(lastContentType).toBe("application/json");
+			expect(JSON.parse(lastBody)).toEqual({ slack_message_ts: "1715000000.000123" });
+		} finally {
+			globalThis.fetch = originalFetch;
+		}
+	});
 
 	test("skips the POST when slack_message_ts is empty (caller must guard)", async () => {
 		const { fn, calls } = makeFetchOk();