feat: add binary activation wire format

tests/test_two_node_pipeline.py

@@ -1,4 +1,4 @@
-"""US-002 integration test: two-node shard pipeline with activation tensors flowing A → B."""
+"""Integration tests for two-node shard pipelines with activation tensors flowing A to B."""
 
 import json
 import urllib.request
@@ -62,3 +62,54 @@ def test_two_node_activation_pipeline():
         gateway.stop()
         node_a.stop()
         node_b.stop()
+
+
+def test_binary_activation_pipeline_chunks_512_token_prefill():
+    node_a = StubNodeServer(shard_start=0, shard_end=15, is_last_shard=False)
+    port_a = node_a.start()
+    node_b = StubNodeServer(shard_start=16, shard_end=31, is_last_shard=True)
+    port_b = node_b.start()
+    gateway = GatewayServer(
+        inference_route=[
+            f"http://127.0.0.1:{port_a}",
+            f"http://127.0.0.1:{port_b}",
+        ]
+    )
+    gateway_port = gateway.start()
+
+    try:
+        prompt = " ".join(f"tok{i}" for i in range(512))
+        payload = json.dumps({
+            "model": "stub-model",
+            "messages": [{"role": "user", "content": prompt}],
+        }).encode()
+        req = urllib.request.Request(
+            f"http://127.0.0.1:{gateway_port}/v1/chat/completions",
+            data=payload,
+            headers={"Content-Type": "application/json"},
+            method="POST",
+        )
+
+        with urllib.request.urlopen(req) as resp:
+            assert resp.status == 200
+            body = json.loads(resp.read())
+
+        assert body["choices"][0]["message"]["content"] == f"stub response to: {prompt}"
+        assert node_a.forward_chunk_count == 4
+        assert node_b.forward_chunk_count == 4
+        assert not node_a.received_activations
+        assert node_b.received_activations
+
+        chunk_responses = gateway.last_binary_chunk_responses
+        assert len(chunk_responses) == 4
+        for index, chunk in enumerate(chunk_responses):
+            assert chunk.shape == [1, 128, 64]
+            assert chunk.dtype == "bfloat16"
+            assert chunk.chunk_index == index
+            assert chunk.chunk_total == 4
+            assert chunk.headers["x-meshnet-wire"] == "2"
+            assert len(chunk.body) == 1 * 128 * 64 * 2
+    finally:
+        gateway.stop()
+        node_a.stop()
+        node_b.stop()