[IAmJSD]

What

Photoshop/Aseprite-style frame animation for layered documents:

• Frame model in the kernel (schist_core::animation): each frame records per-layer visibility, opacity and an integer position offset; delays, loop count (once / N / forever) and Photoshop's "New layers visible in all frames". Create, New (duplicate) Frame, Delete, reorder, reverse, select/step, per-frame or all-frames delay, loop, per-frame layer offset, Make Frames From Layers, Flatten Frames Into Layers, Delete Animation. Every operation is one undoable edit (EditOp::TimelineSet plus the layer-property changes it implies).
• Timeline panel (timeline in the dock, draggable/resizable/hideable and saved in workspace presets like the others; shown when the document has an animation): frame thumbnails (click to select, drag to reorder), transport (first/prev/play-pause/next/last), new/delete frame, delay + apply to all, loop count, onion skin controls, the active layer's offset in this frame, new-layer rule.
• Playback with real timing (scheduled against a clock so slow renders don't drift), honouring the loop count. Display-only: rendered frames are drawn over the canvas; the document, history and dirty flag are untouched. Any command or canvas click stops it.
• Onion skinning: up to 3 previous (red) / next (blue) frames, opacity adjustable, display-only.
• Export (File ▸ Export ▸ Animation…): animated GIF (per-frame or global palette, exact palettes when colours fit, NeuQuant + optional Floyd–Steinberg otherwise, transparency index, disposal Auto/Keep/Background/Previous), APNG (lossless RGBA), animated WebP (lossless; container written per Google's public RIFF spec around image-webp's VP8L output). New crate schist-animation.
• Persistence: private document-level ScAn PSD/PSB block (JSON), following the ScIn pattern. Layers referenced by tree-walk index with name check, falling back to unique-name match, dropping rather than guessing. The current frame is also the layers' normal visibility/opacity. Photoshop's own animation resources are preserved verbatim (not interpreted, no reverse engineering).
• Commands / MCP / actions: 11 animation.* commands registered through the shared registry (so they appear as cmd_animation_* MCP tools and in Spotlight), allowed in recorded actions. Layer ▸ Animation submenu.

Design notes

• The live layers are the current frame. Ordinary edits (eye toggle, opacity, their undo) change the selected frame with no hooks; Timeline::synced reads the live layers back before switching frames, saving or rendering. New layers are materialised into other frames on the next sync using the new-layer rule.
• Offsets have no persistent layer property, so the timeline owns them and render_offset mirrors the current frame's offsets (re-derived whenever TimelineSet is applied, including undo/redo). The Move tool now previews on top of an existing render offset and restores it, so moving pixels in an animated document keeps the frame offset.
• Frame images (thumbnails, playback, onion) are cached on a per-frame content key (resolved layer states + tile fingerprints), not the document revision, so switching frames doesn't invalidate them.
• Crates: gif, png, image-webp, color_quant — all pure Rust, MIT/Apache-2.0 (color_quant MIT), already in Cargo.lock via image, build offline and for wasm. Small binary impact (gif + color_quant are the only newly compiled ones).

Verification done

• cargo test for schist-core (frame ops + undo/redo, offsets through undo, new-layer rule, frame keys), schist-codec-psd (tests/animation.rs: PSD and PSB round trip, re-save, unmatched/renamed layers, unknown block versions and a stand-in Photoshop resource preserved verbatim), schist-commands-core (commands, refusals, everything undoes), schist-animation (encode → decode with the gif, png, image-webp decoders: frame count, delays, loop count, disposal, transparency, lossless pixels), schist-tools-basic (Move keeps the frame offset), schist-app-settings, schist-editor.
• Cross-checked exported files: ffprobe reports 24×16 / 3 frames for GIF and APNG (codec apng); ImageMagick identify reports delays 10/25/4 cs for GIF and WebP and decodes 3 WebP frames (libwebp, independent of our writer).
• cargo clippy -D warnings and cargo fmt on touched crates; make check-i18n.
• i18n: new animation.lang + command.animation.* keys in all 150 locales (AI translations, strict audit passes; human review pending; no/sh generated by tools/sync-i18n.py).

Not verified

• No headless GUI check. Disk on the build box was down to ~11 GB, so the app binary was not built and the Timeline panel, playback, onion skins and the export dialog have not been exercised in a running window. They are covered only by cargo check/clippy and the editor unit tests (424 pass). This is the main thing to try by hand: open a layered document, Layer ▸ Animation ▸ Make Frames From Layers, play, toggle onion skin, drag a frame, File ▸ Export ▸ Animation… (cargo test -p schist-animation also writes anim.psd to $SCHIST_ANIMATION_ARTIFACT_DIR as a ready-made sample).

• Not tested in a real browser build (make check-app-web not run); the code paths are shared and the encoders are pure Rust, but the wasm export path is untested.

• No interactive test of Photoshop opening a Schist-animated PSD (Photoshop shows the selected frame as plain layers; its own timeline is not written).

Limits (documented in docs/frame-animation.md)

• Painting on a layer whose current-frame offset is non-zero paints in layer coordinates (appears shifted).
• Playback/onion skins hidden while the view is rotated; rendered at ≤2048 px.
• GIF delays < 20 ms written as 20 ms; WebP lossless only; no import of animated files as timelines; Photoshop animation data not read; Cloud collaborative sessions don't sync the timeline; no tweening.

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