fix: skip blank/whitespace-only lines in receive loop

_receive_loop only checked for EOF (b""), but blank lines like b"\n"
or b"\r\n" are truthy and reached json.loads(), causing JSONDecodeError.
Strip each line and skip when empty before parsing.

Author: aorumbayev

src/acp/connection.py

@@ -151,6 +151,9 @@ async def _receive_loop(self) -> None:
                 line = await self._reader.readline()
                 if not line:
                     break
+                line = line.strip()
+                if not line:
+                    continue
                 try:
                     message: dict[str, Any] = json.loads(line)
                 except Exception:

tests/test_rpc.py

@@ -316,6 +316,20 @@ async def test_ignore_invalid_messages(connect, server):
         await asyncio.wait_for(server.client_reader.readline(), timeout=0.1)
 
 
+@pytest.mark.asyncio
+async def test_blank_lines_skipped(connect, server):
+    connect(connect_agent=True, connect_client=False)
+
+    for noise in [b"\n", b"  \n", b"\r\n"]:
+        server.client_writer.write(noise)
+    req = {"jsonrpc": "2.0", "id": 1, "method": "initialize", "params": {"protocolVersion": 1}}
+    server.client_writer.write((json.dumps(req) + "\n").encode())
+    await server.client_writer.drain()
+
+    resp = json.loads(await asyncio.wait_for(server.client_reader.readline(), timeout=1))
+    assert resp["id"] == 1 and "result" in resp
+
+
 class _ExampleAgent(Agent):
     __test__ = False