mcp: allow configuring protocol version

Closes #2023

src/mcp/Server.zig

@@ -114,7 +114,7 @@ test "MCP.Server - Integration: synchronous smoke test" {
 
     try router.processRequests(server, &in_reader);
 
-    try testing.expectJson(.{ .jsonrpc = "2.0", .id = 1 }, out_alloc.writer.buffered());
+    try testing.expectJson(.{ .jsonrpc = "2.0", .id = 1, .result = .{ .protocolVersion = "2025-11-25" } }, out_alloc.writer.buffered());
 }
 
 test "MCP.Server - Integration: ping request returns an empty result" {

src/mcp/protocol.zig

@@ -1,5 +1,14 @@
 const std = @import("std");
 
+pub const Version = enum {
+    @"2024-11-05",
+    @"2025-03-26",
+    @"2025-06-18",
+    @"2025-11-25",
+
+    pub const latest: Version = .@"2025-11-25";
+};
+
 pub const Request = struct {
     jsonrpc: []const u8 = "2.0",
     id: ?std.json.Value = null,

src/mcp/router.zig

@@ -81,8 +81,8 @@ pub fn handleMessage(server: *Server, arena: std.mem.Allocator, msg: []const u8)
 
 fn handleInitialize(server: *Server, req: protocol.Request) !void {
     const id = req.id orelse return;
-    const result = protocol.InitializeResult{
-        .protocolVersion = "2025-11-25",
+    const result: protocol.InitializeResult = .{
+        .protocolVersion = server.app.config.mcpVersion(),
         .capabilities = .{
             .resources = .{},
             .tools = .{},
@@ -121,7 +121,7 @@ test "MCP.router - handleMessage - synchronous unit tests" {
         \\{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test-client","version":"1.0.0"}}}
     );
     try testing.expectJson(
-        \\{ "jsonrpc": "2.0", "id": 1, "result": { "capabilities": { "tools": {} } } }
+        \\{ "jsonrpc": "2.0", "id": 1, "result": { "protocolVersion": "2025-11-25", "capabilities": { "tools": {} } } }
     , out_alloc.writer.buffered());
     out_alloc.writer.end = 0;