- new primitives: clip_toggle_enabled (per-block flip), clip_set_linked,
sequence_add_default_transition (config-driven, sequence timebase),
node_set_label_many, node_set_color_label, plus observation getters
- toggle-links, default transitions, enable toggles, color labels, and
block renaming now go through the facade; the stray empty undo entry
from block renaming is gone along the way
- nest/multicam/waveform-sync stay as documented composites: they mix
redo_now intermediate state, graph surgery, and app-side computation
that a single primitive cannot express faithfully
- the timeline panel's command execution paths are now fully migrated