WIP: refactor: add remote_roundtrip_test

test/remote_child_roundtrip.zig

@@ -0,0 +1,24 @@
+/// Child process for the remoting round-trip test.
+/// Reads one framed CBOR message from stdin, expects ["ping"],
+/// and replies with ["pong"] on stdout.
+const std = @import("std");
+const cbor = @import("cbor");
+const framing = @import("framing");
+
+pub fn main() !void {
+    var acc: framing.Accumulator = .{};
+    var read_buf: [4096]u8 = undefined;
+
+    const frame = while (true) {
+        const n = try std.fs.File.stdin().read(&read_buf);
+        if (n == 0) return error.UnexpectedEof;
+        if (acc.feed(read_buf[0..n])) |f| break f;
+    };
+
+    if (!try cbor.match(frame, .{"ping"})) return error.UnexpectedMessage;
+
+    var msg_buf: [64]u8 = undefined;
+    var stream: std.Io.Writer = .fixed(&msg_buf);
+    try cbor.writeValue(&stream, .{"pong"});
+    try framing.write_frame(std.fs.File.stdout(), stream.buffered());
+}