add_effect ran effect.apply and then one prop.set per `values` entry as
separate commands: each became its own undo step, and a bad value (an
unknown parameter id) returned an error but left the effect, and any
values set before it, on the layer, so a corrected retry landed at
effects/#2.
It now runs them as one engine.batch, named like effect.apply's own undo
step ("Apply Gaussian Blur"): one undo removes the effect with its values,
and a failing step rolls the whole call back. The reply is unchanged.
Test: add_effect_is_one_undo_step_and_all_or_nothing.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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