fix(brainbar): stabilize json-rpc envelope order

brain-bar/Sources/BrainBar/BrainBarServer.swift

@@ -402,7 +402,7 @@ final class BrainBarServer: @unchecked Sendable {
             framed = data
         } else {
             // Newline-delimited JSON-RPC (Claude Code v2.1+ / MCP 2025-11-25)
-            guard let jsonData = try? JSONSerialization.data(withJSONObject: response) else { return false }
+            guard let jsonData = try? MCPFraming.encodeJSONResponse(response) else { return false }
             var data = jsonData
             data.append(0x0A) // trailing \n
             framed = data

brain-bar/Sources/BrainBar/MCPFraming.swift

@@ -113,15 +113,45 @@ struct MCPFraming: Sendable {
 
     /// Encode a JSON-RPC response with Content-Length framing.
     static func encode(_ response: [String: Any]) throws -> Data {
-        let jsonData = try JSONSerialization.data(withJSONObject: response)
+        let jsonData = try encodeJSONResponse(response)
         let header = "Content-Length: \(jsonData.count)\r\n\r\n"
         var frame = Data(header.utf8)
         frame.append(jsonData)
         return frame
     }
 
+    /// Encode JSON-RPC envelopes with a deterministic top-level key order.
+    ///
+    /// Claude Desktop currently rejects otherwise-valid JSON-RPC objects when
+    /// Foundation serializes `result` or `id` before `jsonrpc`.
+    static func encodeJSONResponse(_ response: [String: Any]) throws -> Data {
+        guard let jsonrpc = response["jsonrpc"],
+              let id = response["id"],
+              response["result"] != nil || response["error"] != nil else {
+            return try JSONSerialization.data(withJSONObject: response)
+        }
+
+        var data = Data("{\"jsonrpc\":".utf8)
+        data.append(try encodeJSONValue(jsonrpc))
+        data.append(Data(",\"id\":".utf8))
+        data.append(try encodeJSONValue(id))
+        if let result = response["result"] {
+            data.append(Data(",\"result\":".utf8))
+            data.append(try encodeJSONValue(result))
+        } else if let error = response["error"] {
+            data.append(Data(",\"error\":".utf8))
+            data.append(try encodeJSONValue(error))
+        }
+        data.append(0x7D) // }
+        return data
+    }
+
     // MARK: - Private
 
+    private static func encodeJSONValue(_ value: Any) throws -> Data {
+        try JSONSerialization.data(withJSONObject: value, options: [.fragmentsAllowed])
+    }
+
     private func parseContentLength(_ header: String) -> Int? {
         for line in header.split(separator: "\r\n") {
             let trimmed = line.trimmingCharacters(in: .whitespaces)

brain-bar/Tests/BrainBarTests/MCPFramingTests.swift

@@ -113,6 +113,27 @@ final class MCPFramingTests: XCTestCase {
         XCTAssertTrue(str.contains("protocolVersion"))
     }
 
+    func testEncodesJSONRPCEnvelopeWithJSONRPCFirst() throws {
+        let response: [String: Any] = [
+            "id": 2,
+            "jsonrpc": "2.0",
+            "result": [
+                "tools": [
+                    ["name": "brain_search"]
+                ]
+            ] as [String: Any]
+        ]
+
+        let framed = try MCPFraming.encode(response)
+        let frame = try XCTUnwrap(String(data: framed, encoding: .utf8))
+        let body = try XCTUnwrap(frame.components(separatedBy: "\r\n\r\n").last)
+
+        XCTAssertTrue(
+            body.hasPrefix(#"{"jsonrpc":"2.0","id":2,"result":"#),
+            "Claude Desktop expects the JSON-RPC envelope to serialize with jsonrpc first; got: \(body.prefix(80))"
+        )
+    }
+
     // MARK: - Empty body
 
     func testRejectsZeroContentLength() {

brain-bar/Tests/BrainBarTests/MCPRouterTests.swift

@@ -140,6 +140,24 @@ final class MCPRouterTests: XCTestCase {
         XCTAssertEqual(toolNames, expected)
     }
 
+    func testEncodedToolsListEnvelopeStartsWithJSONRPC() throws {
+        let router = MCPRouter()
+        let response = router.handle([
+            "jsonrpc": "2.0",
+            "id": 2,
+            "method": "tools/list",
+        ])
+
+        let framed = try MCPFraming.encode(response)
+        let frame = try XCTUnwrap(String(data: framed, encoding: .utf8))
+        let body = try XCTUnwrap(frame.components(separatedBy: "\r\n\r\n").last)
+
+        XCTAssertTrue(
+            body.hasPrefix(#"{"jsonrpc":"2.0","id":2,"result":"#),
+            "Claude Desktop expects jsonrpc to be the first envelope key for tools/list; got: \(body.prefix(80))"
+        )
+    }
+
     func testEachToolHasInputSchema() throws {
         let router = MCPRouter()
         let request: [String: Any] = [