fix(cztomczak#676): reference and debug-log the NULL-browser fallback in cookie filter

The IO-thread CanSendCookie/CanSaveCookie callbacks can receive a CefFrame
whose GetBrowser() returns NULL; the early-return fallbacks were previously
silent and unexplained.

- frame.pyx GetPyFrame(): comment now explains when GetBrowser() is NULL off
  the UI thread (IO-thread cookie callbacks, cross-origin subresource requests,
  service workers / CefURLRequest).
- cookie_access_filter.pyx CanSendCookie/CanSaveCookie: log the
  no-resolvable-browser fallback and cite the CEF header doc
  (cef_resource_request_handler.h > CefCookieAccessFilter).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: linesight

src/frame.pyx

@@ -30,12 +30,15 @@ cdef PyFrame GetPyFrame(CefRefPtr[CefFrame] cefFrame):
     cdef CefString frameId = cefFrame.get().GetIdentifier()
     cdef CefRefPtr[CefBrowser] cefBrowser = cefFrame.get().GetBrowser()
     if not cefBrowser.get():
-        # GetBrowser() can return NULL when a frame is being created or
-        # destroyed during rapid navigation (e.g. iframes on heavy pages).
+        # Issue #676: CefFrame::GetBrowser() may return NULL when called off
+        # the UI thread -- e.g. from the IO-thread CanSendCookie/CanSaveCookie
+        # callbacks for cross-origin subresource requests, or for requests not
+        # associated with a live frame (service workers / CefURLRequest).
         # Raising here prevents a SIGSEGV from the naked .get().GetIdentifier()
-        # chain that was here before this check.
+        # chain that was previously here. Callers that can hit this (the cookie
+        # filter) guard for it and fall back before calling GetPyFrame.
         raise Exception("GetPyFrame(): CefBrowser is NULL"
-                        " (frame lifecycle transition during navigation?)")
+                        " (CefFrame.GetBrowser() unavailable off the UI thread?)")
     cdef int browserId = cefBrowser.get().GetIdentifier()
     if not browserId:
         raise Exception("GetPyFrame(): browserId is 0 (browser not yet initialised)")

src/handlers/cookie_access_filter.pyx

@@ -25,8 +25,17 @@ cdef public cpp_bool CookieAccessFilter_CanSendCookie(
         # browser was closed.
         if IsBrowserClosed(cef_browser):
             return False
-        if not cef_frame.get().GetBrowser().get():
-            return True  # default: allow cookie
+        # Issue #676: This callback runs on the IO thread, where
+        # CefFrame::GetBrowser() may return NULL (observed for cross-origin
+        # subresource requests). CEF also documents browser/frame as optional
+        # ("may be NULL for requests originating from service workers or
+        # CefURLRequest", cef_resource_request_handler.h > CefCookieAccessFilter).
+        # Without a resolvable browser we cannot build a PyFrame to dispatch on,
+        # so log and allow the cookie by default (CEF's own default is true).
+        if not cef_frame.get() or not cef_frame.get().GetBrowser().get():
+            Debug("CanSendCookie: no resolvable browser for the request"
+                  " (IO-thread / service-worker request); allowing by default")
+            return True
 
         browser = GetPyBrowser(cef_browser, "CanSendCookie")
         frame = GetPyFrame(cef_frame)
@@ -66,8 +75,14 @@ cdef public cpp_bool CookieAccessFilter_CanSaveCookie(
         # browser was closed.
         if IsBrowserClosed(cef_browser):
             return False
-        if not cef_frame.get().GetBrowser().get():
-            return True  # default: allow cookie
+        # Issue #676: see CanSendCookie above. On the IO thread
+        # CefFrame::GetBrowser() may be NULL (and CEF documents browser/frame
+        # as optional). Without a resolvable browser we cannot build a PyFrame,
+        # so log and allow the cookie by default.
+        if not cef_frame.get() or not cef_frame.get().GetBrowser().get():
+            Debug("CanSaveCookie: no resolvable browser for the request"
+                  " (IO-thread / service-worker request); allowing by default")
+            return True
 
         browser = GetPyBrowser(cef_browser, "CanSaveCookie")
         frame = GetPyFrame(cef_frame)