Auto-restart HTTP server when binary changes

Checks binary mtime every 10 requests. If the binary has been
rebuilt, closes the listen socket and exec's itself. No more
stale server after builds.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hosts/ocaml/bin/sx_server.ml

@@ -2658,10 +2658,30 @@ let http_mode port =
   Unix.bind sock (Unix.ADDR_INET (Unix.inet_addr_any, port));
   Unix.listen sock 1024;
   Printf.eprintf "[sx-http] Listening on port %d (%d render workers, non-blocking)\n%!" port n_workers;
+
+  (* Auto-restart: check if binary has changed every N requests *)
+  let binary_path = Sys.executable_name in
+  let binary_mtime = try (Unix.stat binary_path).Unix.st_mtime with _ -> 0.0 in
+  let request_count = ref 0 in
+  let check_interval = 10 in  (* check every 10 requests *)
+  let check_restart () =
+    incr request_count;
+    if !request_count mod check_interval = 0 then begin
+      let current_mtime = try (Unix.stat binary_path).Unix.st_mtime with _ -> 0.0 in
+      if current_mtime > binary_mtime then begin
+        Printf.eprintf "[sx-http] Binary changed, restarting...\n%!";
+        (* Close listen socket, then exec self *)
+        Unix.close sock;
+        Unix.execv binary_path (Array.of_list (Array.to_list Sys.argv))
+      end
+    end
+  in
+
   (try
     while true do
       (* Accept a connection *)
       let (client, _addr) = Unix.accept sock in
+      check_restart ();
       (* Read request — non-blocking: set a short timeout *)
       Unix.setsockopt_float client Unix.SO_RCVTIMEO 5.0;
       Unix.setsockopt_float client Unix.SO_SNDTIMEO 10.0;