diff --git a/integrations/agent-plugin-core/typescript/src/telemetry.ts b/integrations/agent-plugin-core/typescript/src/telemetry.ts
index 656ed9858..0beffe6b9 100644
--- a/integrations/agent-plugin-core/typescript/src/telemetry.ts
+++ b/integrations/agent-plugin-core/typescript/src/telemetry.ts
@@ -94,12 +94,19 @@ export function createTelemetry(config: TelemetryConfig) {
   const maxQueueSize = config.maxQueueSize ?? 100;
 
   const deliver = config.delivery ?? (async (batch: Record<string, unknown>[]) => {
-    await fetch(POSTHOG_BATCH_URL, {
+    const response = await fetch(POSTHOG_BATCH_URL, {
       method: "POST",
       headers: { "Content-Type": "application/json" },
       body: JSON.stringify({ api_key: POSTHOG_API_KEY, batch }),
       signal: AbortSignal.timeout(3_000),
     });
+    // fetch only rejects on a network-level failure. Without this check a 500,
+    // a 503 or a 429 resolved normally and the batch was counted as delivered
+    // and dropped, which is the likelier outage than a refused connection.
+    // Any non-2xx is retried, matching the Python core: the backoff and the
+    // queue bound contain a payload that will never be accepted, because the
+    // re-queued batch sits at the front and is the first thing evicted.
+    if (!response.ok) throw new Error(`posthog responded ${response.status}`);
   });
 
   async function flush(): Promise<void> {
diff --git a/integrations/agent-plugin-core/typescript/tests/telemetry.test.ts b/integrations/agent-plugin-core/typescript/tests/telemetry.test.ts
index 3e5ab9fba..5a8ca0439 100644
--- a/integrations/agent-plugin-core/typescript/tests/telemetry.test.ts
+++ b/integrations/agent-plugin-core/typescript/tests/telemetry.test.ts
@@ -214,3 +214,46 @@ test("a long outage costs the oldest events, not unbounded memory", async () =>
   assert.ok(telemetry.queueForTesting().length <= 3, "queue grew past maxQueueSize");
   telemetry.resetForTesting();
 });
+
+test("an HTTP error response is a failure, not a delivery", async () => {
+  // fetch only rejects on a network-level failure, so a 500 used to resolve
+  // normally and the batch was dropped as delivered. Exercises the real default
+  // delivery path rather than an injected one, which is where this hid.
+  const realFetch = globalThis.fetch;
+  let calls = 0;
+  globalThis.fetch = (async () => {
+    calls += 1;
+    return new Response("upstream is unwell", { status: 503 });
+  }) as typeof fetch;
+
+  const telemetry = createTelemetry({
+    host: "h", source: "S", version: "1", distinctId: "d", flushThreshold: 1000,
+  });
+  try {
+    telemetry.capture("during.outage");
+    await telemetry.flush();
+
+    assert.equal(calls, 1, "never reached the network");
+    assert.equal(telemetry.queueForTesting().length, 1, "a 503 was counted as delivered");
+  } finally {
+    globalThis.fetch = realFetch;
+    telemetry.resetForTesting();
+  }
+});
+
+test("a 2xx is a delivery", async () => {
+  const realFetch = globalThis.fetch;
+  globalThis.fetch = (async () => new Response("ok", { status: 200 })) as typeof fetch;
+
+  const telemetry = createTelemetry({
+    host: "h", source: "S", version: "1", distinctId: "d", flushThreshold: 1000,
+  });
+  try {
+    telemetry.capture("fine");
+    await telemetry.flush();
+    assert.equal(telemetry.queueForTesting().length, 0, "a good response did not clear the queue");
+  } finally {
+    globalThis.fetch = realFetch;
+    telemetry.resetForTesting();
+  }
+});