fix(electrobun): X11 XMoveResizeWindow bypass for resize (no GTK involvement)

begin_resize_drag + XUngrabPointer still fails because GTK's layout
cycle re-asserts WebView preferred size, fighting the WM resize.

New approach: JS mousemove → XMoveResizeWindow via libX11.so.6 FFI.
Completely bypasses GTK size negotiation. GTK only receives
ConfigureNotify after the X server has already resized the window.

Added: x11SetFrame() using gdk_x11_display_get_xdisplay +
gdk_x11_window_get_xid + XMoveResizeWindow.

ui-electrobun/src/bun/gtk-window.ts

@@ -27,6 +27,7 @@ function getX11() {
     x11 = dlopen("libX11.so.6", {
       XUngrabPointer: { args: [FFIType.ptr, FFIType.u64], returns: FFIType.i32 },
       XFlush: { args: [FFIType.ptr], returns: FFIType.i32 },
+      XMoveResizeWindow: { args: [FFIType.ptr, FFIType.u64, FFIType.i32, FFIType.i32, FFIType.u32, FFIType.u32], returns: FFIType.i32 },
     });
     return x11;
   } catch { return null; }
@@ -38,6 +39,7 @@ function getGdk() {
     gdk3 = dlopen("libgdk-3.so.0", {
       gdk_display_get_default: { args: [], returns: FFIType.ptr },
       gdk_x11_display_get_xdisplay: { args: [FFIType.ptr], returns: FFIType.ptr },
+      gdk_x11_window_get_xid: { args: [FFIType.ptr], returns: FFIType.u64 },
     });
     return gdk3;
   } catch { return null; }
@@ -151,6 +153,11 @@ function getGtk() {
         args: [FFIType.ptr],
         returns: FFIType.void,
       },
+      // Get GdkWindow from GtkWidget (needed for X11 window ID)
+      gtk_widget_get_window: {
+        args: [FFIType.ptr],
+        returns: FFIType.ptr,
+      },
       // Sensitivity (disable input processing on widget)
       gtk_widget_set_sensitive: {
         args: [FFIType.ptr, FFIType.bool],
@@ -266,6 +273,42 @@ function forceSmallMinSize(lib: NonNullable<typeof gtk3>, windowPtr: any) {
   } catch { /* ignore */ }
 }
 
+/**
+ * Set window frame directly via X11, BYPASSING GTK's size negotiation.
+ * GTK receives ConfigureNotify after the fact and adjusts.
+ * This prevents the WebView's preferred size from fighting the resize.
+ */
+export function x11SetFrame(
+  windowPtr: number | bigint,
+  x: number, y: number, width: number, height: number,
+): boolean {
+  const gtkLib = getGtk();
+  const gdkLib = getGdk();
+  const x11Lib = getX11();
+  if (!gtkLib || !gdkLib || !x11Lib) return false;
+  try {
+    const gdkDisplay = gdkLib.symbols.gdk_display_get_default();
+    if (!gdkDisplay) return false;
+    const xDisplay = gdkLib.symbols.gdk_x11_display_get_xdisplay(gdkDisplay);
+    if (!xDisplay) return false;
+    const gdkWindow = gtkLib.symbols.gtk_widget_get_window(windowPtr as any);
+    if (!gdkWindow) return false;
+    const xid = gdkLib.symbols.gdk_x11_window_get_xid(gdkWindow);
+    if (!xid) return false;
+    x11Lib.symbols.XMoveResizeWindow(
+      xDisplay, xid,
+      Math.round(x), Math.round(y),
+      Math.max(400, Math.round(width)),
+      Math.max(300, Math.round(height)),
+    );
+    x11Lib.symbols.XFlush(xDisplay);
+    return true;
+  } catch (err) {
+    console.error("[gtk-window] x11SetFrame failed:", err);
+    return false;
+  }
+}
+
 /**
  * Delegate resize to the window manager.
  * Releases X11 grabs first (SDL2 pattern) so WM can take the pointer.

ui-electrobun/src/bun/index.ts

@@ -161,6 +161,13 @@ const rpc = BrowserView.defineRPC<PtyRPCSchema>({
           return { ok };
         } catch (err) { console.error("[window.gtkSetFrame]", err); return { ok: false }; }
       },
+      "window.x11SetFrame": ({ x, y, width, height }: { x: number; y: number; width: number; height: number }) => {
+        try {
+          const { x11SetFrame } = require("./gtk-window.ts");
+          const ok = x11SetFrame((mainWindow as any).ptr, x, y, width, height);
+          return { ok };
+        } catch (err) { console.error("[window.x11SetFrame]", err); return { ok: false }; }
+      },
     },
     messages: {},
   },