Looks like this is causing a leak:
==623237== 254 (144 direct, 110 indirect) bytes in 1 blocks are definitely lost in loss record 35,810 of 41,691
==623237==    at 0x4E116A9: g_type_create_instance (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.7701.0)
==623237==    by 0x4DF4E7F: ??? (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.7701.0)
==623237==    by 0x4DF6FB2: g_object_new_valist (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.7701.0)
==623237==    by 0x4DF7308: g_object_new (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.7701.0)
==623237==    by 0x4F79E67: gtk_file_chooser_native_new (in /usr/lib/x86_64-linux-gnu/libgtk-4.so.1.1000.5)
==623237==    by 0x4F86063: ??? (in /usr/lib/x86_64-linux-gnu/libgtk-4.so.1.1000.5)
==623237==    by 0x4F86866: gtk_file_dialog_save (in /usr/lib/x86_64-linux-gnu/libgtk-4.so.1.1000.5)
==623237==    by 0x48A5AA7: save_cb (pidgindebug.c:182)
==623237==    by 0x4DEF5F0: ??? (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.7701.0)
==623237==    by 0x4E03A72: ??? (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.7701.0)
==623237==    by 0x4E09551: g_signal_emit_valist (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.7701.0)
==623237==    by 0x4E095FE: g_signal_emit (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.7701.0)

Ship It!

Looks good for now. We could probably do with some helpers for setting the initial folders and stuff, but it's fine to skip that stuff for now.
Also I'm not so worried about the ignored errors for now as the request and whiteboard api both need another round of cleanup / redesign anyways.

Ship It!

Great work, thanks!!