mcp: refactor for testability and add comprehensive test suite

- Refactor mcp.Server and router to accept injected I/O streams.
- Implement McpHarness for high-fidelity MCP integration testing.
- Add unit tests for protocol, tools, and resources modules.
- Add integration tests covering initialization, tool/resource execution, and error handling.
- Improve error reporting for malformed JSON requests.

src/mcp/resources.zig

@@ -105,3 +105,21 @@ pub fn handleRead(server: *Server, arena: std.mem.Allocator, req: protocol.Reque
         return server.sendError(req.id.?, .InvalidRequest, "Resource not found");
     }
 }
+
+const testing = @import("../testing.zig");
+
+test "resource_list contains expected resources" {
+    try testing.expect(resource_list.len >= 2);
+    try testing.expectString("mcp://page/html", resource_list[0].uri);
+    try testing.expectString("mcp://page/markdown", resource_list[1].uri);
+}
+
+test "ReadParams parsing" {
+    var arena = std.heap.ArenaAllocator.init(testing.allocator);
+    defer arena.deinit();
+    const aa = arena.allocator();
+
+    const raw = "{\"uri\": \"mcp://page/html\"}";
+    const parsed = try std.json.parseFromSlice(ReadParams, aa, raw, .{});
+    try testing.expectString("mcp://page/html", parsed.value.uri);
+}