Protect transfer.kill() the way transfer.abort() is protected

Transfer.abort() is protected from aborting the transfer while inside of a
libcurl callback (since libcurl doesn't support mutating the easy while inside
of a callback AND it causes issues in the zig code).

This applies similar logic to Transfer.kill() which is less likely to be called
but worse if it is called in a callback, as transfer.kill() deinit's the
transfer - something the callback caller is not expecting. Since killing isn't
safe to do, we flag the transfer as aborted AND null/noop all the callbacks.

Fixes WPT crash /content-security-policy/frame-src/frame-src-blocked-path-matching.sub.html

src/Config.zig

@@ -24,7 +24,6 @@ const log = @import("log.zig");
 const dump = @import("browser/dump.zig");
 
 const WebBotAuthConfig = @import("network/WebBotAuth.zig").Config;
-const mcp = @import("mcp.zig");
 
 pub const RunMode = enum {
     help,
@@ -189,13 +188,6 @@ pub fn webBotAuth(self: *const Config) ?WebBotAuthConfig {
     };
 }
 
-pub fn mcpVersion(self: *const Config) []const u8 {
-    return switch (self.mode) {
-        .mcp => |opts| @tagName(opts.version),
-        else => @tagName(mcp.Version.default),
-    };
-}
-
 pub fn maxConnections(self: *const Config) u16 {
     return switch (self.mode) {
         .serve => |opts| opts.cdp_max_connections,
@@ -230,7 +222,6 @@ pub const Serve = struct {
 
 pub const Mcp = struct {
     common: Common = .{},
-    version: mcp.Version = .default,
 };
 
 pub const DumpFormat = enum {
@@ -462,13 +453,6 @@ pub fn printUsageAndExit(self: *const Config, success: bool) void {
         \\Starts an MCP (Model Context Protocol) server over stdio
         \\Example: {s} mcp
         \\
-        \\Options:
-        \\--version
-        \\                Override the reported MCP version.
-        \\                Valid: 2024-11-05, 2025-03-26, 2025-06-18, 2025-11-25.
-        \\                Can also be set via LIGHTPANDA_MCP_VERSION env var.
-        \\                Defaults to "2024-11-05".
-        \\
     ++ common_options ++
         \\
         \\version command
@@ -656,25 +640,10 @@ fn parseMcpArgs(
     allocator: Allocator,
     args: *std.process.ArgIterator,
 ) !Mcp {
-    var result: Mcp = .{};
-    var env_ver: ?[]const u8 = null;
-    var arg_ver: ?[]const u8 = null;
-
-    if (std.posix.getenv("LIGHTPANDA_MCP_VERSION")) |ver| {
-        env_ver = ver;
-    }
+    var mcp: Mcp = .{};
 
     while (args.next()) |opt| {
-        if (std.mem.eql(u8, "--version", opt)) {
-            const str = args.next() orelse {
-                log.fatal(.mcp, "missing argument value", .{ .arg = opt });
-                return error.InvalidArgument;
-            };
-            arg_ver = str;
-            continue;
-        }
-
-        if (try parseCommonArg(allocator, opt, args, &result.common)) {
+        if (try parseCommonArg(allocator, opt, args, &mcp.common)) {
             continue;
         }
 
@@ -682,15 +651,7 @@ fn parseMcpArgs(
         return error.UnkownOption;
     }
 
-    const final_ver = arg_ver orelse env_ver;
-    if (final_ver) |ver| {
-        result.version = std.meta.stringToEnum(mcp.Version, ver) orelse {
-            log.fatal(.mcp, "invalid protocol version", .{ .value = ver });
-            return error.InvalidArgument;
-        };
-    }
-
-    return result;
+    return mcp;
 }
 
 fn parseFetchArgs(

src/browser/HttpClient.zig

@@ -821,16 +821,16 @@ fn processOneMessage(self: *Client, msg: http.Handles.MultiMessage, transfer: *T
         break :blk std.ascii.eqlIgnoreCase(hdr.value, "close");
     };
 
-    if (msg.err != null and !is_conn_close_recv) {
-        transfer.requestFailed(transfer._callback_error orelse msg.err.?, true);
-        return true;
-    }
-
     // make sure the transfer can't be immediately aborted from a callback
     // since we still need it here.
     transfer._performing = true;
     defer transfer._performing = false;
 
+    if (msg.err != null and !is_conn_close_recv) {
+        transfer.requestFailed(transfer._callback_error orelse msg.err.?, true);
+        return true;
+    }
+
     if (!transfer._header_done_called) {
         // In case of request w/o data, we need to call the header done
         // callback now.
@@ -873,7 +873,6 @@ fn processMessages(self: *Client) !bool {
     var processed = false;
     while (self.handles.readMessage()) |msg| {
         const transfer = try Transfer.fromConnection(&msg.conn);
-
         const done = self.processOneMessage(msg, transfer) catch |err| blk: {
             log.err(.http, "process_messages", .{ .err = err, .req = transfer });
             transfer.requestFailed(err, true);
@@ -1068,6 +1067,24 @@ pub const Transfer = struct {
         if (self.req.shutdown_callback) |cb| {
             cb(self.ctx);
         }
+
+        if (self._performing or self.client.performing) {
+            // We're currently inside of a callback. This client, and libcurl
+            // generally don't expect a transfer to become deinitialized during
+            // a callback. We can flag the transfer as aborted (which is what
+            // we do when transfer.abort() is called in this condition) AND,
+            // since this "kill()"should prevent any future callbacks, the best
+            // we can do is null/noop them.
+            self.aborted = true;
+            self.req.start_callback = null;
+            self.req.shutdown_callback = null;
+            self.req.header_callback = Noop.headerCallback;
+            self.req.data_callback = Noop.dataCallback;
+            self.req.done_callback = Noop.doneCallback;
+            self.req.error_callback = Noop.errorCallback;
+            return;
+        }
+
         self.deinit();
     }
 
@@ -1492,3 +1509,12 @@ pub const Transfer = struct {
         return null;
     }
 };
+
+const Noop = struct {
+    fn headerCallback(_: *Transfer) !bool {
+        return true;
+    }
+    fn dataCallback(_: *Transfer, _: []const u8) !void {}
+    fn doneCallback(_: *anyopaque) !void {}
+    fn errorCallback(_: *anyopaque, _: anyerror) void {}
+};

src/mcp.zig

@@ -1,7 +1,6 @@
 const std = @import("std");
 
 pub const protocol = @import("mcp/protocol.zig");
-pub const Version = protocol.Version;
 pub const router = @import("mcp/router.zig");
 pub const Server = @import("mcp/Server.zig");
 

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, .result = .{ .protocolVersion = "2024-11-05" } }, out_alloc.writer.buffered());
+    try testing.expectJson(.{ .jsonrpc = "2.0", .id = 1 }, out_alloc.writer.buffered());
 }
 
 test "MCP.Server - Integration: ping request returns an empty result" {

src/mcp/protocol.zig

@@ -1,14 +1,5 @@
 const std = @import("std");
 
-pub const Version = enum {
-    @"2024-11-05",
-    @"2025-03-26",
-    @"2025-06-18",
-    @"2025-11-25",
-
-    pub const default: Version = .@"2024-11-05";
-};
-
 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 = server.app.config.mcpVersion(),
+    const result = protocol.InitializeResult{
+        .protocolVersion = "2025-11-25",
         .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": { "protocolVersion": "2024-11-05", "capabilities": { "tools": {} } } }
+        \\{ "jsonrpc": "2.0", "id": 1, "result": { "capabilities": { "tools": {} } } }
     , out_alloc.writer.buffered());
     out_alloc.writer.end = 0;