fix(vpui): 建窗失败改为可见错误上报；Scene3D 加分步诊断打点

背景：Tk.mainloop 的循环条件是 window.is_active(win_id)，而 is_active 对 win_id < 0 直接返回 0 ⇒ 一旦 create_window 失败，app 一次循环都不进、一句日志都不打就 process.exit(0)（现场：Scene3D spawn 后静默退出，「没有窗口」就是这么来的）。改动：window.vp 的 _attach / _connect / create_window 四个失败返回点补 [win] 错误上报（open 失败 / mmap 失败 / desk 未就绪超时 / 请求环压入失败 / CREATED 超时），这些是错误可见性而非临时噪音，长期保留；Scene3D/main.vp 加 _dbg 分步打点（start / tk ok / canvas ok / scene ok / geometry 后的 win_id 与 buf / 渲染线程 / mainloop 返回），用于定位它到底死在哪一步，定位完成后撤除。

Apps/Scene3D/main.vp

@@ -1,8 +1,10 @@
 import vpsdk.window as window
 import vpsdk.process as process
 import vpsdk.vpui as vpui
+import vpsdk.devfs as devfs
 import string
 from stdint import *
+import viperlib
 import gfx
 
 define SCENE_W = 640
@@ -20,6 +22,11 @@ _time_val: float = float(0.0)
 # （x 变大后相邻采样点的相位差被量化 ⇒ 曲线塌成一条平线、热力图颜色失去层次）。
 define TIME_WRAP = float(12.566370614359172)
 
+def _dbg(msg: const str):
+    # 【诊断·临时】与 explorer 同路径的串口输出。app 在建窗失败时会**静默退出**
+    # （Tk.mainloop 的循环条件是 win_id 有效，win_id=-1 时一次都不循环），所以必须分步打点。
+    devfs.serial_puts(msg)
+
 def _render_thread(arg: t.CPtr):
     global _time_val
     root: vpui.Tk* = _root_ptr
@@ -34,13 +41,16 @@ def _render_thread(arg: t.CPtr):
 
 @__attribute__(section(".text.startup"), aligned(16))
 export def _start() -> int:
+    _dbg("[s3d] start\n")
     root: vpui.Tk = vpui.Tk()
+    _dbg("[s3d] tk ok\n")
     root.title("3D Scene")
     root.set_style(window.STYLE_WIN11)
     root.bg_color = uint32(0x0F0F19)
     master: vpui.Tk* = &root
 
     canvas: vpui.FBCanvas = vpui.FBCanvas(master, SCENE_W, SCENE_H)
+    _dbg("[s3d] canvas ok\n")
     root.pack(0, vpui.PACK_TOP, vpui.FILL_BOTH, 1, 0, 0)
 
     zbuf: float* = &_zbuf_mem
@@ -51,8 +61,13 @@ export def _start() -> int:
     canvas.set_fb(fb, SCENE_W, SCENE_H)
 
     s3d: gfx.Scene3D = gfx.Scene3D(fb, zbuf, SCENE_W, SCENE_H)
+    _dbg("[s3d] scene ok\n")
 
     root.geometry(100, 30, SCENE_W, SCENE_H + 32)
+    _wbuf: [128]char
+    viperlib.snprintf(&_wbuf, 128, "[s3d] geometry win_id=%d buf=0x%lx\n",
+                      root.win_id, uint64(root.buf))
+    _dbg(&_wbuf)
 
     global _root_ptr, _canvas_ptr, _s3d_ptr
 
@@ -61,8 +76,10 @@ export def _start() -> int:
     _s3d_ptr = &s3d
 
     process.thread_create(_render_thread, None)
+    _dbg("[s3d] render thread created\n")
 
     root.mainloop()
+    _dbg("[s3d] mainloop returned\n")
 
     process.exit(0)
     return 0

vpsdk/window.vp

@@ -1,6 +1,7 @@
 import vpsdk.desk as desk
 import vpsdk.process as process
 import vpsdk.stdlib as stdlib    # 不能删：app 的裸名 malloc 靠它把 stdlib 拉进链接图
+import vpsdk.devfs as devfs
 import string
 
 
@@ -81,6 +82,7 @@ def _attach() -> int:
     if _state < 0: return -1
     b: uint64 = desk.desk_map(_fd)
     if b == 0:
+        devfs.serial_puts("[win] desk mmap FAILED\n")
         _state = -1
         return -1
     i: int = 0
@@ -88,6 +90,7 @@ def _attach() -> int:
         process.yield_cpu()
         i += 1
     if desk.desk_ready(b) == 0:
+        devfs.serial_puts("[win] desk not ready (attach timeout)\n")
         _state = -1
         return -1
     _base = b
@@ -101,6 +104,7 @@ def _connect() -> int:
     if _state < 0: return -1
     fd: int = desk.desk_open()
     if fd < 0:
+        devfs.serial_puts("[win] open /dev/desk FAILED\n")
         _state = -1
         return -1
     _fd = fd
@@ -132,9 +136,14 @@ def _slot(win: int) -> desk.WinSlot*:
 
 
 def create_window(x: int, y: int, w: int, h: int, title: const str, style: int) -> int:
-    if _connect() != 0: return -1
+    # 建窗失败必须**可见**：Tk.mainloop 的循环条件是 window.is_active(win_id)，win_id = -1
+    # 时一次都不循环就返回 ⇒ app 一句日志都没有就 exit（现场：Scene3D spawn 后静默退出）。
+    if _connect() != 0:
+        devfs.serial_puts("[win] create_window: connect FAILED\n")
+        return -1
     if _my_pid < 0: return -1
     if _send(uint32(desk.DESK_REQ_CREATE), 0, x, y, w, h, title) != 0:
+        devfs.serial_puts("[win] create_window: request ring push FAILED\n")
         return -1
     # 等 CREATED 答复（win_id 由 explorer 分配）。建窗通常在 app 初始化阶段、
     # 事件环是空的；这期间若弹到非 CREATED 事件（属于本进程的其它窗口输入）就丢弃，
@@ -146,6 +155,7 @@ def create_window(x: int, y: int, w: int, h: int, title: const str, style: int)
                 return _evt.a
         process.yield_cpu()
         i += 1
+    devfs.serial_puts("[win] create_window: CREATED timeout\n")
     return -1
 
 def get_winbuf(win_id: int) -> uint32*: