photoshop_apply_gradient_mask

Apply a linear black-to-white gradient on the active layer mask channel (fade/blend). Users often say: fade into background, gradient mask, blend subject, soft edge fade. This paints on an existing layer mask — not a Gradient Fill layer. Use when: softening edges or fading a layer into the background through its mask. Do NOT use when: subject is not isolated — use photoshop_recipe_remove_background or photoshop_create_layer_mask first. Returns: JSON { ok, summary, details: { applied, direction, angle, mask_auto_created? } }. Preconditions: active document and active layer. Creates a reveal-all mask if none exists. Side effects: modifies layer mask pixels; two history steps when mask is auto-created.