fix(acp): a blank line from an ACP agent no longer ends the session

packages/effect-acp/src/protocol.test.ts

@@ -310,6 +310,31 @@ it.layer(NodeServices.layer)("effect-acp protocol", (it) => {
     }),
   );
 
+  it.effect("skips blank lines between agent messages", () =>
+    Effect.gen(function* () {
+      const { stdio, input } = yield* makeInMemoryStdio();
+      const outcome = yield* Deferred.make<string>();
+      const transport = yield* AcpProtocol.makeAcpPatchedProtocol({
+        stdio,
+        serverRequestMethods: new Set(),
+        onTermination: (error) => Deferred.succeed(outcome, error._tag).pipe(Effect.asVoid),
+      });
+      yield* transport.incoming.pipe(
+        Stream.runForEach((notification) => Deferred.succeed(outcome, notification._tag)),
+        Effect.forkScoped,
+      );
+
+      const update = encodeUnknownJsonString({
+        jsonrpc: "2.0",
+        method: "session/update",
+        params: { sessionId: "session-1", update: { sessionUpdate: "plan", entries: [] } },
+      });
+      yield* Queue.offer(input, encoder.encode(`\n\r\n \t\n${update}\n\n`));
+
+      assert.equal(yield* Deferred.await(outcome), "SessionUpdate");
+    }),
+  );
+
   it.effect("logs decode failures without copying the cause or wire payload", () =>
     Effect.gen(function* () {
       const secret = "acp-wire-secret-sentinel";

packages/effect-acp/src/protocol.ts

@@ -162,7 +162,7 @@ const decodeElicitationComplete = Schema.decodeUnknownEffect(
 );
 const parserFactory = RpcSerialization.ndJsonRpc();
 // ndJsonRpc skips lines that are not JSON. A malformed agent line has to end the
-// session, so frames are split here and each one goes through the strict codec.
+// session, so frames are split here and each nonblank one goes through the strict codec.
 const makeStrictNdJsonRpcParser = () => {
   const codec = RpcSerialization.jsonRpc().makeUnsafe();
   const decoder = new TextDecoder();
@@ -172,7 +172,7 @@ const makeStrictNdJsonRpcParser = () => {
       buffer += typeof bytes === "string" ? bytes : decoder.decode(bytes, { stream: true });
       const lines = buffer.split("\n");
       buffer = lines.pop() ?? "";
-      return lines.flatMap((line) => codec.decode(line));
+      return lines.flatMap((line) => (line.trim() === "" ? [] : codec.decode(line)));
     },
     encode: (response: Parameters<typeof codec.encode>[0]) => {
       const encoded = codec.encode(response);