Gateway: catch a zero-height window whenever it happens, not just once (#67)

Reproduced on beryllium 2026-09-22 -- the first repro this bug has had.
The window comes up showing nothing but its title bar, with

  Gtk-CRITICAL: gtk_window_resize: assertion 'height > 0' failed

on stderr, and no resize handle to recover with. Crucially it is
INTERMITTENT: the same binary, same machine, same session starts
correctly most times. That is the signature of the wx3.2/GTK3 layout
reentrancy class CLAUDE.md describes, not of a deterministic path --
which also explains why it was never reproducible on the machine it was
originally reported against.

The existing safety net only ran once, at the end of the constructor,
so it could only catch a bad size that was already in place by then. It
now also runs on EVT_SIZE.

Two things it deliberately does NOT do: it does not call SetSize() from
inside the size handler, since that is the very reentrancy suspected of
causing this -- the correction is deferred with CallAfter() to the next
idle, after the in-flight layout pass has finished. And it guards
against queueing more than one correction at a time.

Still a safety net rather than a root cause: it makes the window usable
instead of leaving a title bar the user cannot resize. The root cause
needs someone with the repro to catch it in the act.

Unrelated and still unexplained: the same machine also saw a one-off
"free(): invalid size" at startup, which did not recur under gdb. Not
addressed here; do not assume this commit fixes it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EFMUNbw2UpRPmgsqviAowb

Author: andy

src/apps/gateway/Gateway.C

@@ -52,6 +52,7 @@ BEGIN_EVENT_TABLE( Gateway, wxFrame )
 
   EVT_CLOSE( Gateway::OnCloseWindow )
   EVT_ICONIZE( Gateway::OnIconize )
+  EVT_SIZE( Gateway::OnSize )
   EVT_TIMER( wxID_ANY, Gateway::OnTimer )
 
 END_EVENT_TABLE()
@@ -107,6 +108,7 @@ Gateway::Gateway( GatewayApp* app, wxWindow* parent,
   // has realized it. Constructing the timer first left it attached to an
   // unrealized wxFrame -- wx2.8's GTK timer path tolerated that silently,
   // but wx3.2 asserts on it (harmless spam, but noisy and worth not doing).
+  p_fixingSize = false;
   p_timer = new wxTimer(this);
 
   SetIcon(wxIcon(ewxBitmap::pixmapFile("gateway64.xpm"), wxBITMAP_TYPE_XPM));
@@ -134,6 +136,52 @@ Gateway::Gateway( GatewayApp* app, wxWindow* parent,
 }
 
 
+/**
+ * Keep the window from being left with no usable height (GitHub #67).
+ *
+ * The constructor already clamps a non-positive size once, but that only
+ * catches it if the bad size is in place by then. Reproduced on beryllium
+ * 2026-09-22: the window comes up showing nothing but its title bar, with
+ * "gtk_window_resize: assertion 'height > 0' failed" on stderr -- and it is
+ * INTERMITTENT, which is the signature of the wx3.2/GTK3 layout reentrancy
+ * class documented in CLAUDE.md rather than of a deterministic path. A
+ * one-shot check at construction cannot catch a zero height that arrives
+ * later.
+ *
+ * Deliberately does not call SetSize() from inside the size handler: that
+ * is the very reentrancy that causes this. CallAfter() defers the
+ * correction to the next idle, by which time the in-flight layout pass has
+ * finished.
+ *
+ * This is still a safety net, not a root cause. It makes the window usable
+ * instead of leaving the user with a title bar and no way to resize it.
+ */
+void Gateway::OnSize(wxSizeEvent& event)
+{
+  event.Skip();
+
+  int width, height;
+  GetSize(&width, &height);
+  if (width > 0 && height > 0) return;
+
+  // One correction at a time -- without this, a window that keeps being
+  // resized to zero would queue an unbounded number of them.
+  if (p_fixingSize) return;
+  p_fixingSize = true;
+
+  CallAfter([this, width, height]() {
+    int w, h;
+    GetSize(&w, &h);
+    if (w <= 0 || h <= 0) {
+      std::cerr << "Gateway: window came up " << w << "x" << h
+           << " (GitHub #67); forcing a usable size." << std::endl;
+      SetSize(w <= 0 ? 68 : w, h <= 0 ? 68 : h);
+    }
+    p_fixingSize = false;
+  });
+}
+
+
 /**
  * Destructor.
  *

src/apps/gateway/Gateway.H

@@ -92,6 +92,8 @@ protected:
 
   void OnCloseWindow(wxCloseEvent& event);
   void OnIconize(wxIconizeEvent &event);
+  // GitHub #67: clamp a zero-height window, deferred to avoid reentrancy.
+  void OnSize(wxSizeEvent& event);
   void OnTimer(wxTimerEvent& event);
   void OnMenuClick(wxCommandEvent& event);
 
@@ -107,6 +109,7 @@ protected:
   short p_pixmapIndex;
   GatewayPrefs * p_prefsDlg;
   wxTimer* p_timer;
+  bool p_fixingSize;
 
   GatewayApp* p_app;