ComfyUI wipes temp/ on every server start and emits a cached `executed`
event for cached nodes (replaying the prior session's UI output with a
filename that no longer exists on disk). The frontend grade panel then
hits a 404 in /api/view when fetching the input EXR.
Fixes:
- color_grade.py: GearColorGrade.IS_CHANGED returns a unique value per
call, forcing re-execution every run. The grade pipeline + one EXR
write is cheap relative to upstream inference, and guarantees the
preview file is on disk whenever the panel opens.
- gear_grade.js: fetchBytes now attaches HTTP status to the thrown
error; onIframeReady catches 404 specifically, drops the stale map
entries, and surfaces a useful message instead of the raw error.
Mohamed Oumoumad
1f1c1e4623