- nodeparamview: add visited set to get_distance_between_nodes, fixing
unbounded recursion (stack overflow) when the node graph has a cycle
- viewerdisplay: give texture_ a consistent owner via assign_texture();
borrowed queue textures are now retained, created ones freed, fixing
a dangling pointer that corrupted the heap and crashed in the GL driver
- playbackcache: resignal_requests() iterates a copy, handlers may
clear_request_range() while iterating (ASan container-overflow)
- preview C API: preview request ticket lambdas captured the request
state raw; after oakengine_preview_request_free the ticket outlived
the request and the finished callback wrote into freed memory
(heap-use-after-free). The finished flag is now a shared_ptr captured
weakly by the callbacks
- playback: oak_playback_frame regains a timestamp (num/den) filled
from olive::Frame; the viewer queue append no longer uses Rational()
for every frame, which made append_timewise drop all but the first
frame and froze the picture during playback
- mainwindow: open_node_in_viewer refuses sequence nodes; sequences
already have the Sequence Viewer, and saved layouts could otherwise
resurrect a redundant floating Viewer bound to the sequence