photoshop_recipe_sky_blend

One-shot sky composite: places an external sky image, adds a layer mask, and applies a horizon gradient fade. Wrapped in a single undoable history step. Users often say: replace sky, fix blown sky, better clouds, swap sky background. Use when: the user provides a sky image path and native sky replacement is unavailable or manual blend is preferred. Do NOT use when: no sky_image_path is available — ask the user for an absolute file path first. Do NOT use when: fading the active subject layer only — use photoshop_recipe_gradient_fade. Returns: { ok, summary, undo_history_states_consumed, details: { sky_image_path, layer_name, horizon_pct, feather_pct, direction } }. Preconditions: active document; sky image file must exist on disk. Side effects: adds a placed sky layer with gradient mask; one undo reverts everything.