refactor(engine): move error, services, document state, event, fonts and Session methods out of lib.rs

crates/engine/src/cmd.rs

@@ -156,6 +156,7 @@ mod enabled;
 mod params;
 mod schema;
 
+use super::*;
 pub use enabled::always;
 pub(crate) use enabled::{has_comp, has_keys, has_layers, has_project_selection, not_yet, not_yet_run};
 pub use params::match_path_of;
@@ -280,3 +281,14 @@ pub fn find(id: &str) -> Option<&'static CommandSpec> {
     });
     index.get(id).map(|&i| &command_specs()[i])
 }
+
+/// Font families available to text layers (bundled + scanned system fonts).
+/// Text animation presets: (id, name), for menus.
+pub fn text_presets() -> Vec<(String, String)> {
+    commands::text_preset_list()
+}
+
+/// Built-in animation presets (Effects & Presets ▸ * Animation Presets): (id, name, category).
+pub fn animation_presets() -> Vec<(String, String, String)> {
+    commands::builtin_preset_list()
+}

crates/engine/src/doc_state.rs

@@ -0,0 +1,197 @@
+use super::*;
+
+/// A keyframe reference: layer, property uid, key time (layer time).
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub struct KeyRef {
+    pub layer: LayerId,
+    pub prop: Uid,
+    pub time: Tick,
+}
+
+/// A keyframe drag in progress (`keys.move` steps sharing a merge key): the selection it
+/// started from and the total offset so far, so every step is applied to the keys as they were
+/// before the drag. A key passed over on the way is never overwritten; only the drop position
+/// counts, as in After Effects.
+#[derive(Clone, Debug)]
+pub struct KeyMove {
+    pub merge: String,
+    pub from: Vec<KeyRef>,
+    pub total: Tick,
+}
+
+/// Keyframes of one property on the keyframe clipboard.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct KeyClip {
+    pub layer: LayerId,
+    /// Match-id path relative to the layer (`transform/position`), portable between layers.
+    pub path: String,
+    /// Keys with times relative to the earliest copied key (layer time).
+    pub keys: Vec<effectcraft_keyframe::Keyframe>,
+}
+
+/// A selected mask vertex: layer, mask group uid, vertex index.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub struct VertexRef {
+    pub layer: LayerId,
+    pub mask: Uid,
+    pub index: usize,
+}
+
+/// One composition's selection. The active comp's copy lives in [`EditorState::selected_layers`]
+/// (and the property, key, and vertex lists); every other comp keeps its own here (#1001).
+#[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize)]
+pub struct CompSelection {
+    pub layers: Vec<LayerId>,
+    pub props: Vec<(LayerId, Uid)>,
+    pub keys: Vec<KeyRef>,
+    pub vertices: Vec<VertexRef>,
+}
+
+impl CompSelection {
+    pub(crate) fn is_empty(&self) -> bool {
+        self.layers.is_empty() && self.props.is_empty() && self.keys.is_empty() && self.vertices.is_empty()
+    }
+}
+
+/// Editing state that commands depend on (headless-relevant, serde for agents).
+#[derive(Clone, Debug, Default, Serialize, Deserialize)]
+pub struct EditorState {
+    pub active_comp: Option<ItemId>,
+    /// Open compositions (viewer/timeline tabs), in tab order.
+    pub open_comps: Vec<ItemId>,
+    /// Compositions that were active before the current one, most recent first (Shift+Esc).
+    #[serde(default)]
+    pub recent_comps: Vec<ItemId>,
+    /// Current time per comp (the CTI).
+    pub times: std::collections::BTreeMap<ItemId, Tick>,
+    /// Layer selection of the active comp. Other comps' selections are in [`Self::comp_selections`].
+    pub selected_layers: Vec<LayerId>,
+    /// Selections of comps that are not active, keyed by comp id (#1001).
+    #[serde(default)]
+    pub comp_selections: std::collections::BTreeMap<ItemId, CompSelection>,
+    /// Selected properties / groups (by uid) of selected layers.
+    pub selected_props: Vec<(LayerId, Uid)>,
+    pub selected_keys: Vec<KeyRef>,
+    pub project_selection: Vec<ItemId>,
+    /// Layer clipboard (serialized layers) and keyframe clipboard.
+    #[serde(skip)]
+    pub clipboard: Vec<Layer>,
+    /// Copied keyframes (times relative to the earliest copied key).
+    #[serde(skip)]
+    pub key_clipboard: Vec<KeyClip>,
+    /// The last copy was keyframes (Paste pastes keys at the CTI).
+    #[serde(skip)]
+    pub clip_is_keys: bool,
+    /// Values of selected unanimated properties (match path, value), copied with Edit ▸ Copy;
+    /// Paste sets the same properties of the selected layers.
+    #[serde(skip)]
+    pub value_clipboard: Vec<(String, effectcraft_keyframe::Value)>,
+    /// Copied effect instances, with comp-time key offsets from the earliest copied key.
+    /// Paste adds them to the selected layers at the destination comp's CTI.
+    #[serde(skip)]
+    pub effect_clipboard: Vec<effectcraft_project::PropGroup>,
+    /// Copied shape items (Edit ▸ Copy with groups, paths, paints or path operations selected in
+    /// a shape layer's Contents); Paste adds them to the selected shape layers.
+    #[serde(skip)]
+    pub contents_clipboard: Vec<effectcraft_project::PropGroup>,
+    /// Selected mask vertices (viewer Selection tool / pen).
+    #[serde(default)]
+    pub selected_vertices: Vec<VertexRef>,
+    pub snapping: bool,
+    /// Tools bar ▸ Snapping options (which features snap, Snap Edges Extended).
+    #[serde(default)]
+    pub snap_features: viewer::SnapFeatures,
+    /// Last applied effect id (Effect ▸ last effect).
+    pub last_effect: Option<String>,
+    /// Viewer region of interest `[x, y, w, h]` in comp pixels (Composition ▸ Crop Comp to Region
+    /// of Interest).
+    #[serde(default)]
+    pub region_of_interest: Option<[f64; 4]>,
+    /// Property-link clipboard (Edit ▸ Copy with Property Links / Copy Expression Only).
+    #[serde(skip)]
+    pub link_clipboard: Option<LinkClip>,
+    /// File ▸ Interpret Footage ▸ Remember Interpretation.
+    #[serde(skip)]
+    pub interpretation: Option<effectcraft_project::Footage>,
+    /// Viewer 3D view per comp (Active Camera / Front / … / Custom View 3 and edited view cameras).
+    #[serde(default)]
+    pub views3d: std::collections::BTreeMap<ItemId, effectcraft_render::three_d::Views3D>,
+    /// Tracker panel ▸ Current Track: (tracked layer, tracker group uid) in the active comp.
+    #[serde(default)]
+    pub current_track: Option<(LayerId, Uid)>,
+    /// Tracker panel ▸ Method in mask mode (Track Mask).
+    #[serde(default)]
+    pub mask_track_method: mask_track::MaskMethod,
+    /// 3D Camera Tracker: the selected track points (ids) in the viewer.
+    #[serde(default)]
+    pub camera_points: Vec<u32>,
+    /// Mask Interpolation panel options.
+    #[serde(default)]
+    pub mask_interp: commands::mask_interp::MaskInterpOptions,
+    /// Paint and Brushes panel options (Brush, Clone Stamp and Eraser tools).
+    #[serde(default)]
+    pub paint: commands::paint::PaintOptions,
+    /// Roto Brush and Refine Edge tool options.
+    #[serde(default)]
+    pub roto: roto::RotoOptions,
+    /// Puppet tool options for new meshes.
+    #[serde(default)]
+    pub puppet: commands::puppet::PuppetOptions,
+    /// The shape tools' and the Pen's options (Tool Creates Shape / Mask, Fill and Stroke).
+    #[serde(default)]
+    pub shape_tool: commands::shape_tool::ShapeTool,
+    /// View ▸ Switch View Layout: 1, 2 or 4 views side by side in the Composition viewer.
+    #[serde(default = "one_view")]
+    pub view_layout: u8,
+    /// View ▸ Switch View Layout ▸ Share View Options (grid, guides… in every view).
+    #[serde(default)]
+    pub share_view_options: bool,
+    /// Layer ▸ Mask ▸ Hide Locked Masks (viewer outlines).
+    #[serde(default)]
+    pub hide_locked_masks: bool,
+    /// On-canvas text editing (Type tool): the edited layer, selection and insertion style.
+    #[serde(default)]
+    pub text_edit: Option<commands::text_edit::TextEdit>,
+    /// Text copied while editing (with its formatting), for Paste / Paste Text Formatting Only.
+    #[serde(skip)]
+    pub text_clipboard: Option<effectcraft_keyframe::TextDoc>,
+    /// Composition viewer display options (Show Channel, exposure, snapshot, Fast Previews).
+    #[serde(default)]
+    pub viewer: commands::viewer_cmds::ViewOptions,
+    /// Essential Graphics panel ▸ Primary composition (`None` = the active comp).
+    #[serde(default)]
+    pub essential_primary: Option<ItemId>,
+    /// Essential Graphics panel ▸ Solo Supported Properties (the timeline shows only properties
+    /// Essential Graphics can expose).
+    #[serde(default)]
+    pub essential_solo: bool,
+    /// File ▸ Watch Folder: the folder being watched for projects to render (frontends call
+    /// `file.watchFolder.poll` periodically while it is set).
+    #[serde(default)]
+    pub watch_folder: Option<String>,
+    /// The Footage panel: the footage shown, its time and In/Out marks (source time).
+    #[serde(default)]
+    pub footage_panel: Option<commands::footage_panel::FootageView>,
+    /// Media Browser: the folder shown and the favourites.
+    #[serde(default)]
+    pub media_browser: media_browser::BrowserState,
+    /// Content-Aware Fill panel settings.
+    #[serde(default)]
+    pub content_fill: commands::content_fill::FillSettings,
+    /// View ▸ Split with New Locked Viewer: the second viewer's comp and 3D view.
+    #[serde(default)]
+    pub locked_viewer: Option<commands::viewer_cmds::LockedViewer>,
+}
+
+fn one_view() -> u8 {
+    1
+}
+
+/// What Copy with Property Links / Copy Expression Only put on the clipboard.
+#[derive(Clone, Debug, PartialEq)]
+pub enum LinkClip {
+    /// Expressions that link back to the source properties: (match path, expression text).
+    Links { relative: bool, links: Vec<(String, String)> },
+    /// Expressions only: (match path, expression).
+    Expressions(Vec<(String, effectcraft_project::Expression)>),
+}

crates/engine/src/error.rs

@@ -0,0 +1,20 @@
+#[derive(Debug, thiserror::Error)]
+pub enum EngineError {
+    #[error("unknown command `{0}`")]
+    UnknownCommand(String),
+    #[error("command `{0}` is not available right now: {1}")]
+    Disabled(String, String),
+    #[error("invalid parameters for `{cmd}`: {msg}")]
+    BadParams { cmd: String, msg: String },
+    #[error("no active composition")]
+    NoComp,
+    /// A `comp` reference (name or id) that names no composition.
+    #[error("no composition {0}")]
+    NoSuchComp(String),
+    #[error("{0}")]
+    Project(#[from] effectcraft_project::ProjectError),
+    #[error("{0}")]
+    Other(String),
+}
+
+pub type Result<T> = std::result::Result<T, EngineError>;

crates/engine/src/event.rs

@@ -0,0 +1,32 @@
+use super::*;
+
+/// Events for frontends (drained each frame).
+#[derive(Clone, Debug, PartialEq, Serialize)]
+pub enum Event {
+    ProjectChanged {
+        revision: u64,
+    },
+    Toast {
+        message: String,
+        error: bool,
+    },
+    OpenComp(ItemId),
+    OpenUrl(String),
+    /// A frontend-only command (viewer zoom, panels, dialogs…) ran: the UI performs it. Headless
+    /// sessions ignore these.
+    Frontend {
+        command: String,
+        params: Value,
+    },
+    /// Drop cached frames / renders (Edit ▸ Purge).
+    PurgeCaches,
+    /// Put an image on the system clipboard (Composition ▸ Copy Frame to Clipboard): `rgba` is
+    /// `width` × `height` straight-alpha RGBA8 rows. Headless sessions ignore it; the pixels are
+    /// not serialized.
+    CopyImage {
+        width: u32,
+        height: u32,
+        #[serde(skip)]
+        rgba: Vec<u8>,
+    },
+}

crates/engine/src/fonts.rs

@@ -0,0 +1,92 @@
+use super::*;
+
+pub fn text_families() -> Vec<String> {
+    effectcraft_text::families().into_iter().map(|(f, _)| f).collect()
+}
+
+/// The styles a family offers (its own faces, in weight order), for the style menus. A family
+/// that isn't installed offers the usual styles, which resolve to Inter's.
+pub fn font_styles(family: &str) -> Vec<String> {
+    effectcraft_text::families()
+        .into_iter()
+        .find(|(f, _)| f.eq_ignore_ascii_case(family))
+        .map(|(_, st)| st)
+        .filter(|st| !st.is_empty())
+        .unwrap_or_else(|| ["Regular", "Medium", "SemiBold", "Bold", "Italic"].iter().map(|s| s.to_string()).collect())
+}
+
+/// The OpenType feature tags (GSUB / GPOS) of the face a family + style resolves to.
+pub fn font_features(family: &str, style: &str) -> Vec<String> {
+    effectcraft_text::fonts::face(effectcraft_text::resolve(family, style).face).features()
+}
+
+/// One row of the Character panel's font menu.
+#[derive(Clone, Debug, PartialEq)]
+pub struct FontRow {
+    /// The family to apply (empty for the separator after the recent fonts).
+    pub family: String,
+    /// What the menu shows: the English family name, or the font's own-language name when
+    /// Settings ▸ Type ▸ Show Font Names in English is off.
+    pub display: String,
+    pub recent: bool,
+    /// A variable font (the menu's Variable Fonts filter keeps only these).
+    pub variable: bool,
+}
+
+/// Outline polylines of "Sample" set in `family` at `size` px (baseline at y = 0, y down), for
+/// the font menu's preview (Settings ▸ Type ▸ Show Font Preview).
+pub fn font_preview(family: &str, size: f64) -> Vec<Vec<[f32; 2]>> {
+    use kurbo::PathEl;
+    let st = effectcraft_keyframe::text_doc::CharStyle { font: family.to_string(), size, ..Default::default() };
+    let mut out = vec![];
+    let mut x = 0.0;
+    for ch in "Sample".chars() {
+        let (path, adv) = effectcraft_text::char_glyph_style(&st, ch);
+        let mut cur: Vec<[f32; 2]> = vec![];
+        let pt = |p: kurbo::Point| [(p.x + x) as f32, p.y as f32];
+        kurbo::flatten(&path, 0.2, |el| match el {
+            PathEl::MoveTo(p) => {
+                if cur.len() > 1 {
+                    out.push(std::mem::take(&mut cur));
+                }
+                cur = vec![pt(p)];
+            }
+            PathEl::LineTo(p) => cur.push(pt(p)),
+            PathEl::ClosePath => {
+                if let Some(f) = cur.first().copied() {
+                    cur.push(f);
+                }
+                if cur.len() > 1 {
+                    out.push(std::mem::take(&mut cur));
+                }
+            }
+            _ => {}
+        });
+        if cur.len() > 1 {
+            out.push(cur);
+        }
+        x += adv;
+    }
+    out
+}
+
+/// The Character panel's font menu: the recent fonts (Settings ▸ Type ▸ Number of Recent Fonts
+/// to Display), a separator, then every family. Each row says whether the family is variable,
+/// for the menu's Variable Fonts filter.
+pub fn font_menu(prefs: &prefs::Prefs) -> Vec<FontRow> {
+    let all = text_families();
+    let native = if prefs.type_.font_names_in_english { Default::default() } else { effectcraft_text::fonts::native_families() };
+    let variable = effectcraft_text::fonts::variable_families();
+    let row = |f: &String, recent: bool| FontRow {
+        family: f.clone(),
+        display: native.get(f).cloned().unwrap_or_else(|| f.clone()),
+        recent,
+        variable: variable.contains(f),
+    };
+    let mut out: Vec<FontRow> = prefs.recent_fonts_shown().iter().filter(|f| all.contains(f)).map(|f| row(f, true)).collect();
+    if !out.is_empty() {
+        out.push(FontRow { family: String::new(), display: "-".into(), recent: false, variable: false });
+    }
+    out.extend(all.iter().map(|f| row(f, false)));
+    out
+}

crates/engine/src/services.rs

@@ -0,0 +1,65 @@
+use super::*;
+
+/// Host services (file access) injected by the frontend.
+pub trait Services: Send + Sync {
+    fn read_file(&self, path: &str) -> std::io::Result<Vec<u8>>;
+    fn write_file(&self, path: &str, data: &[u8]) -> std::io::Result<()>;
+    /// Whether a file exists (the background footage check after open).
+    fn exists(&self, path: &str) -> bool {
+        std::path::Path::new(path).exists()
+    }
+    /// A file's size and modification time (nanoseconds since 1970), to notice that it changed
+    /// on disk (Settings ▸ Import ▸ Reload Footage Changed on Disk); `None` when it can't be read.
+    fn stamp(&self, path: &str) -> Option<(u64, u128)> {
+        let meta = std::fs::metadata(path).ok()?;
+        let modified = meta.modified().ok()?.duration_since(std::time::UNIX_EPOCH).ok()?;
+        Some((meta.len(), modified.as_nanos()))
+    }
+    /// Keep a file the app made for itself (footage extracted from a template): like
+    /// [`Services::write_file`], creating its folder, but never offered as a download (web: it
+    /// goes to browser storage only).
+    fn store_file(&self, path: &str, data: &[u8]) -> std::io::Result<()> {
+        if let Some(d) = std::path::Path::new(path).parent().filter(|d| !d.as_os_str().is_empty()) {
+            let _ = std::fs::create_dir_all(d);
+        }
+        self.write_file(path, data)
+    }
+    /// The files in folder `dir` (full paths; no folders, no hidden files), for image-sequence
+    /// detection on import. Empty when it can't be read.
+    fn list_dir(&self, dir: &str) -> Vec<String> {
+        let Ok(rd) = std::fs::read_dir(if dir.is_empty() { "." } else { dir }) else { return vec![] };
+        rd.filter_map(|e| e.ok())
+            .filter(|e| e.file_type().is_ok_and(|t| t.is_file()) && !e.file_name().to_string_lossy().starts_with('.'))
+            .map(|e| e.path().to_string_lossy().to_string())
+            .collect()
+    }
+    /// Whether `path` is a folder (dropped or picked folders import their files).
+    fn is_dir(&self, path: &str) -> bool {
+        std::path::Path::new(path).is_dir()
+    }
+}
+
+/// Native filesystem.
+pub struct FsServices;
+
+impl Services for FsServices {
+    fn read_file(&self, path: &str) -> std::io::Result<Vec<u8>> {
+        std::fs::read(path)
+    }
+    fn write_file(&self, path: &str, data: &[u8]) -> std::io::Result<()> {
+        config::atomic_write(std::path::Path::new(path), data)
+    }
+}
+
+/// Imports media files into the project (implemented by the media layer).
+pub trait Importer: Send + Sync {
+    /// Probe one file and return footage metadata. Image sequences are the engine's
+    /// ([`sequence`]): it groups numbered stills and probes their first file here.
+    fn probe(&self, path: &str) -> std::result::Result<effectcraft_project::Footage, String>;
+    /// A footage file's bytes are now at `path` (extracted from a template): hosts whose media
+    /// layer reads from memory (the browser) register them; file-based ones need nothing.
+    fn register(&self, _path: &str, _data: &[u8]) {}
+    /// An image sequence's other frames (its first was probed) are footage now: hosts whose
+    /// media layer reads from memory (the browser) register them; file-based ones need nothing.
+    fn add_frames(&self, _paths: &[String]) {}
+}

crates/engine/src/session.rs

@@ -0,0 +1,749 @@
+use super::doc_state::{CompSelection, EditorState};
+use super::error::{EngineError, Result};
+use super::event::Event;
+use super::*;
+
+/// `t` as a current time of `comp`: a frame within its duration.
+fn comp_frame_at(comp: &Comp, t: Tick) -> Tick {
+    comp.frame_rate.snap_nearest(t.min(comp.duration - comp.frame_duration()).max(Tick::ZERO))
+}
+
+impl Session {
+    pub fn new() -> Session {
+        Session::default()
+    }
+
+    /// Run a command by id.
+    pub fn execute(&mut self, id: &str, params: Value) -> Result<Value> {
+        let spec = commands::find(id).ok_or_else(|| EngineError::UnknownCommand(id.to_string()))?;
+        if let Err(why) = (spec.enabled)(self) {
+            // Explicit targets (agents, scripts) don't need a UI selection.
+            let explicit = (["layer", "layers", "prop", "keys"].iter().any(|k| params.get(k).is_some()) && commands::has_comp(self).is_ok())
+                || ["item", "items"].iter().any(|k| params.get(k).is_some())
+                // An explicit composition (the enablement looks at the active one).
+                || params.get("comp").is_some_and(|c| !c.is_null() && self.resolve_comp(Some(c)).is_ok());
+            if !explicit {
+                return Err(EngineError::Disabled(id.to_string(), why));
+            }
+        }
+        // Last-resort guard: a panicking command reports an error instead of crashing the app.
+        let r = guard::guarded(&format!("command `{id}`"), || (spec.run)(self, &params))?;
+        self.learn_observe(id, &params);
+        if spec.journal {
+            self.journal.push((id.to_string(), params));
+            if self.journal.len() > 10_000 {
+                self.journal.drain(..1000);
+            }
+        }
+        Ok(r)
+    }
+
+    /// [`Session::execute`] for agents and scripts (MCP, CLI, control channel): unknown top-level
+    /// parameters are rejected with the accepted keys instead of being silently ignored.
+    pub fn execute_checked(&mut self, id: &str, params: Value) -> Result<Value> {
+        let spec = commands::find(id).ok_or_else(|| EngineError::UnknownCommand(id.to_string()))?;
+        commands::check_params(spec, &params)?;
+        self.execute(id, params)
+    }
+
+    /// [`Session::execute`] for a command a script asked for (the JavaScript engine's
+    /// `app.run`, ScriptUI callbacks…). The command and everything it runs count as the script's:
+    /// it may not change the settings that limit scripts (Settings ▸ Scripting & Expressions ▸
+    /// Application Scripting), which only the user can, from the UI, CLI or control channel.
+    pub fn execute_for_script(&mut self, id: &str, params: Value) -> Result<Value> {
+        self.script_calls.0 = self.script_calls.0.saturating_add(1);
+        let r = self.execute(id, params);
+        self.script_calls.0 = self.script_calls.0.saturating_sub(1);
+        r
+    }
+
+    /// Whether the command running was issued by a script ([`Session::execute_for_script`]).
+    pub fn running_for_script(&self) -> bool {
+        self.script_calls.0 > 0
+    }
+
+    /// Whether `id` names a known command whose `enabled` predicate returns `Ok` for this session;
+    /// an unknown id or a predicate error reads as disabled.
+    pub fn is_enabled(&self, id: &str) -> bool {
+        commands::find(id).is_some_and(|c| (c.enabled)(self).is_ok())
+    }
+
+    /// Apply an undoable edit. `merge`: consecutive edits with the same key fold into one step.
+    ///
+    /// Every edit is an external boundary for the on-canvas text editor: if it replaced the
+    /// document the editor is showing, the selection is clamped and the editor gets a fresh IME
+    /// epoch. The editor's own typing goes through `edit_text_doc`, which owns that
+    /// document and must not treat its own keystrokes as a replacement.
+    pub fn edit<T>(&mut self, label: &str, merge: Option<&str>, f: impl FnOnce(&mut Project, &mut EditorState) -> Result<T>) -> Result<T> {
+        let edited = commands::text_edit::active_editor_snapshot(self);
+        let out = self.edit_inner(label, merge, f)?;
+        commands::text_edit::after_external_change(self, edited.as_ref());
+        Ok(out)
+    }
+
+    /// [`Session::edit`] for the on-canvas editor's own text changes. Its document is the one
+    /// the editor owns, so a change here is typing, not a replacement behind the IME's back.
+    pub(crate) fn edit_text_doc<T>(&mut self, label: &str, merge: Option<&str>, f: impl FnOnce(&mut Project, &mut EditorState) -> Result<T>) -> Result<T> {
+        self.edit_inner(label, merge, f)
+    }
+
+    /// The shared body of [`Session::edit`] and [`Session::edit_text_doc`].
+    ///
+    /// Runs `f` on a clone of the project and editor state, then synchronizes derived data (global
+    /// light and Essential Graphics), queues invalidated Warp Stabilizer/camera-tracker work and
+    /// Roto Brush instances needing re-propagation in the `*_pending` lists. If the clone has the same
+    /// content the project and history are left as they were (only editor-state changes from `f`
+    /// are kept) and no revision is bumped; otherwise the previous project is recorded as an
+    /// undo step under `label`, unless it merges with the current merge key (then the redo branch
+    /// is dropped). An `Err` from `f` propagates with the session unchanged.
+    fn edit_inner<T>(&mut self, label: &str, merge: Option<&str>, f: impl FnOnce(&mut Project, &mut EditorState) -> Result<T>) -> Result<T> {
+        let before = self.project.clone();
+        let mut p = (*self.project).clone();
+        let mut st = self.state.clone();
+        let r = f(&mut p, &mut st)?;
+        // Layer styles: one Global Light per comp, whichever layer edited it.
+        effectcraft_project::styles::sync_global_light(&before, &mut p);
+        // Essential Properties of precomp layers follow their comps' Essential Graphics.
+        effectcraft_project::essential::sync_project(&before, &mut p);
+        // Warp Stabilizer analyses made from other frames are cleared (and queued again).
+        for w in warp::invalidate(&before, &mut p) {
+            if !self.warp_pending.contains(&w) {
+                self.warp_pending.push(w);
+            }
+        }
+        // So are 3D Camera Tracker tracks (and solves made with other settings).
+        for w in camera_track::invalidate(&before, &mut p) {
+            if !self.camera_pending.contains(&w) {
+                self.camera_pending.push(w);
+            }
+        }
+        // Roto Brush Input Keys follow the frames; edited instances propagate again.
+        for r in roto::sync(&before, &mut p) {
+            if !self.roto_pending.contains(&r) {
+                self.roto_pending.push(r);
+            }
+        }
+        // Nothing changed (a value set to what it already was): no undo step, not modified.
+        if p.same_content(&before) {
+            self.state = st;
+            return Ok(r);
+        }
+        let same = merge.is_some() && merge.map(str::to_string) == self.history.merge_key;
+        if !same {
+            // Undone steps aren't lost: they stay in the History panel as a branch.
+            let levels = self.prefs.general.undo_levels.max(1) as usize;
+            self.history.record(label, before, levels);
+        } else {
+            self.history.abandon_redo(&before);
+        }
+        self.history.merge_key = merge.map(str::to_string);
+        self.project = Arc::new(p);
+        self.state = st;
+        self.bump();
+        Ok(r)
+    }
+
+    /// Note a change to the on-canvas editor's committed text or session.
+    ///
+    /// Frontends compare this with [`commands::text_edit::ime_stamp_revision`]; an unrelated
+    /// project change must not advance it.
+    pub(crate) fn note_text_edit_change(&mut self) {
+        // Checked process-wide allocation: a stamp is never wrapped or reused. On exhaustion
+        // keep the previous value; an unavailable before/after pair then compares equal and
+        // earns no receipt instead of accepting a stale revision.
+        if let Some(revision) = commands::text_edit::next_ime_revision() {
+            self.ime_revision = self.ime_revision.max(revision);
+        }
+    }
+
+    pub fn bump(&mut self) {
+        self.revision += 1;
+        // Back at the saved state (undo, redo, a history jump or a rolled-back batch).
+        if Arc::ptr_eq(&self.project, &self.saved_project) {
+            self.saved_revision = self.revision;
+        }
+        self.refresh_disk_salt(false);
+        self.events.push(Event::ProjectChanged { revision: self.revision });
+    }
+
+    /// Salt the disk cache's layer keys with the project's footage files
+    /// ([`effectcraft_render::disk_cache::footage_salt`]). Taking it reads the size and time of
+    /// every file, every frame of an image sequence included, so it is taken again only when the
+    /// footage items changed, or with `force` (a project opened, footage reloaded, the disk cache
+    /// attached), not at every edit: with a few large sequences that cost each keystroke in a
+    /// text field over half a second (#1926).
+    pub fn refresh_disk_salt(&mut self, force: bool) -> Option<u64> {
+        use std::hash::{Hash, Hasher};
+        if self.disk_cache.is_none() {
+            self.disk_salt = None;
+            return None;
+        }
+        let mut h = std::collections::hash_map::DefaultHasher::new();
+        for (id, it) in &self.project.items {
+            if let effectcraft_project::ItemKind::Footage(f) = &it.kind {
+                id.hash(&mut h);
+                format!("{f:?}").hash(&mut h);
+            }
+        }
+        let footage = h.finish();
+        if let Some((seen, salt)) = self.disk_salt
+            && seen == footage
+            && !force
+        {
+            return Some(salt);
+        }
+        let salt = effectcraft_render::disk_cache::footage_salt(&self.project);
+        self.disk_salt = Some((footage, salt));
+        self.layer_cache.set_disk_salt(salt);
+        Some(salt)
+    }
+
+    /// Set a comp's Resolution. As in After Effects it is saved with the project (which becomes
+    /// modified) but is no undo step, and it changes no pixels: the comp's cached frames stay
+    /// valid ([`effectcraft_project::Comp::same_pixels`]).
+    pub fn set_resolution(&mut self, comp: ItemId, r: effectcraft_project::Resolution) -> Result<()> {
+        if self.project.comp(comp).ok_or(EngineError::NoComp)?.resolution == r {
+            return Ok(());
+        }
+        Arc::make_mut(&mut self.project).comp_mut(comp).ok_or(EngineError::NoComp)?.resolution = r;
+        self.bump();
+        Ok(())
+    }
+
+    /// Keep what lives outside the undo history (each comp's Resolution) as it is in `from`, the
+    /// project before undo, redo or a history jump restored another state.
+    pub(crate) fn keep_view_settings(&mut self, from: &Project) {
+        let keep: Vec<(ItemId, effectcraft_project::Resolution)> =
+            self.project.comps().filter_map(|(id, c)| from.comp(*id).map(|f| (*id, f.resolution)).filter(|(_, r)| *r != c.resolution)).collect();
+        if keep.is_empty() {
+            return;
+        }
+        let p = Arc::make_mut(&mut self.project);
+        for (id, r) in keep {
+            if let Some(c) = p.comp_mut(id) {
+                c.resolution = r;
+            }
+        }
+    }
+
+    /// Undoes one step: the current project goes onto the redo stack, per-comp Resolution is kept
+    /// as it was, the merge key is cleared, selections are sanitized for the replaced state (the
+    /// on-canvas editor gets a new IME epoch only when its own document changed) and the session is
+    /// bumped. Returns `false`, changing nothing, when there is nothing to undo.
+    pub fn undo(&mut self) -> bool {
+        let Some((label, p)) = self.history.undo.pop() else { return false };
+        let edited = commands::text_edit::active_editor_snapshot(self);
+        let cur = std::mem::replace(&mut self.project, p);
+        self.keep_view_settings(&cur);
+        self.history.redo.push((label, cur));
+        self.history.merge_key = None;
+        self.sanitize_after_replacement(edited.as_ref());
+        self.bump();
+        true
+    }
+
+    /// Redoes one step: the current project goes back onto the undo stack, per-comp Resolution is
+    /// kept, the merge key is cleared, selections are sanitized for the replaced state (a changed
+    /// text document starts a new IME epoch) and the session is bumped. Returns `false`, changing
+    /// nothing, when there is nothing to redo.
+    pub fn redo(&mut self) -> bool {
+        let Some((label, p)) = self.history.redo.pop() else { return false };
+        let edited = commands::text_edit::active_editor_snapshot(self);
+        let cur = std::mem::replace(&mut self.project, p);
+        self.keep_view_settings(&cur);
+        self.history.undo.push((label, cur));
+        self.history.merge_key = None;
+        self.sanitize_after_replacement(edited.as_ref());
+        self.bump();
+        true
+    }
+
+    /// Keep selections valid after the project was replaced by another state (undo, redo, a
+    /// history jump, a rollback): the same layer id can name a different document, so the
+    /// on-canvas editor gets a fresh IME epoch only when its own document changed.
+    ///
+    /// Normally `before` is [`commands::text_edit::active_editor_snapshot`] taken from the
+    /// state this call is about to replace. Atomic batch rollback is the exception: it has
+    /// already restored the pre-batch state and passes the snapshot of the failing intermediate
+    /// state, so a transient restart or component switch inside the batch still rejects reviving
+    /// the old composition. A restored state that still has the same composition, layer and
+    /// editor session and shows byte/style-equivalent text (an opacity or other property undo)
+    /// keeps the editor's owner and selection; a different document, comp, layer or session clamps the
+    /// selection and starts a new epoch. A closed editor stays closed, and a fallback comp's
+    /// matching layer id never inherits the old comp's session. `None` means no editor was open
+    /// when the snapshot was taken; if one is open after the replacement it is treated as an
+    /// unverified document replacement, so it never inherits an old composition.
+    pub fn sanitize_after_replacement(&mut self, before: Option<&commands::text_edit::EditorSnapshot>) {
+        self.sanitize_state();
+        commands::text_edit::after_replacement(self, before);
+    }
+
+    /// Drop selections that no longer exist. Each comp keeps its own selection (#1001); a layer id
+    /// counts only inside the comp that owns it, so the active comp never sees another comp's layers.
+    pub fn sanitize_state(&mut self) {
+        let p = self.project.clone();
+        self.state.open_comps.retain(|c| p.comp(*c).is_some());
+        self.state.comp_selections.retain(|cid, sel| {
+            let Some(c) = p.comp(*cid) else { return false };
+            let ids: Vec<LayerId> = c.layers.iter().map(|l| l.id).collect();
+            sel.layers.retain(|l| ids.contains(l));
+            sel.props.retain(|(l, _)| ids.contains(l));
+            sel.keys.retain(|k| ids.contains(&k.layer));
+            sel.vertices.retain(|v| ids.contains(&v.layer));
+            !sel.is_empty()
+        });
+        if self.state.active_comp.is_some_and(|c| p.comp(c).is_none()) {
+            self.clear_live_selection();
+            // A matching layer id in the fallback comp is not the document being edited.
+            self.state.text_edit = None;
+            self.state.active_comp = self.state.open_comps.first().copied();
+            if let Some(id) = self.state.active_comp {
+                self.recall_selection(id);
+            }
+        }
+        if let Some(c) = self.active_comp() {
+            let ids: Vec<LayerId> = c.layers.iter().map(|l| l.id).collect();
+            self.state.selected_layers.retain(|l| ids.contains(l));
+            self.state.selected_props.retain(|(l, _)| ids.contains(l));
+            self.state.selected_keys.retain(|k| ids.contains(&k.layer));
+            self.state.selected_vertices.retain(|v| ids.contains(&v.layer));
+        }
+        if let Some((l, t)) = self.state.current_track
+            && self.active_comp().and_then(|c| c.layer(l)).and_then(|l| l.tracker(t)).is_none()
+        {
+            self.state.current_track = None;
+        }
+        self.state.project_selection.retain(|i| p.item(*i).is_some());
+        commands::text_edit::sanitize(self);
+    }
+
+    pub fn is_dirty(&self) -> bool {
+        self.revision != self.saved_revision
+    }
+
+    /// The project as it is now is the saved one (after opening or saving it).
+    pub fn mark_saved(&mut self) {
+        self.saved_project = self.project.clone();
+        self.saved_revision = self.revision;
+    }
+
+    /// The project has changes its file doesn't (a session restored with unsaved changes): it
+    /// stays modified until it is saved, whatever is undone.
+    pub fn mark_unsaved(&mut self) {
+        self.saved_project = Arc::new(Project::default());
+        self.bump();
+    }
+
+    pub fn active_comp(&self) -> Option<&Comp> {
+        self.project.comp(self.state.active_comp?)
+    }
+
+    /// [`Session::active_comp`] as a shared snapshot (an `Arc` clone, not a deep copy).
+    pub fn active_comp_arc(&self) -> Option<std::sync::Arc<Comp>> {
+        self.project.comp_arc(self.state.active_comp?)
+    }
+
+    pub fn active_comp_id(&self) -> Option<ItemId> {
+        self.state.active_comp.filter(|c| self.project.comp(*c).is_some())
+    }
+
+    /// Current time of a comp.
+    pub fn time_of(&self, comp: ItemId) -> Tick {
+        self.state.times.get(&comp).copied().unwrap_or(Tick::ZERO)
+    }
+
+    /// Current time of the active comp.
+    pub fn time(&self) -> Tick {
+        self.state.active_comp.and_then(|c| self.state.times.get(&c).copied()).unwrap_or(Tick::ZERO)
+    }
+
+    /// Move the active comp's current time.
+    ///
+    /// Time is an external boundary for the on-canvas text editor too: an animated Source Text
+    /// can show a different document at another time. The document is snapshotted only while an
+    /// editor is open, so playback with no text editor does no text copying.
+    pub fn set_time(&mut self, t: Tick) {
+        if let Some(c) = self.state.active_comp {
+            let t = self.project.comp(c).map_or(t, |comp| comp_frame_at(comp, t));
+            let edited = commands::text_edit::active_editor_snapshot(self);
+            self.state.times.insert(c, t);
+            if self.prefs.general.sync_time_related_items {
+                // Direct call: this `set_time` owns the editor snapshot for both time changes,
+                // so a synced move does not take a second snapshot or start a second epoch.
+                self.sync_related_times_inner(c, t);
+            }
+            commands::text_edit::after_external_change(self, edited.as_ref());
+        }
+    }
+
+    /// Settings ▸ General ▸ Synchronize Time of All Related Items: moving the current time of
+    /// `comp` moves the current time of the comps nested in it (through their precomp layers'
+    /// timing) and of the comps it is nested in, so every related viewer shows the same moment.
+    pub fn sync_related_times(&mut self, comp: ItemId, t: Tick) {
+        // Moving a related comp can move the active one, so the editor's document is checked
+        // here too; the snapshot is skipped entirely when no text editor is open.
+        let edited = commands::text_edit::active_editor_snapshot(self);
+        self.sync_related_times_inner(comp, t);
+        commands::text_edit::after_external_change(self, edited.as_ref());
+    }
+
+    /// Sets the time of every comp related to `comp` through precomp layers: down into the comps
+    /// it nests (through each layer's timing) and up into the comps nesting it. A seen-set keeps
+    /// cycles and diamonds finite; each found time is clamped to its comp's last frame, snapped to
+    /// the nearest frame and stored in `state.times`. The caller owns the text-editor boundary.
+    fn sync_related_times_inner(&mut self, comp: ItemId, t: Tick) {
+        let mut seen = std::collections::BTreeSet::from([comp]);
+        let mut todo = vec![(comp, t)];
+        let mut found = vec![];
+        while let Some((cid, ct)) = todo.pop() {
+            if cid != comp {
+                found.push((cid, ct));
+            }
+            let Some(c) = self.project.comp(cid) else { continue };
+            // Down: the comps this one nests.
+            for l in &c.layers {
+                if let effectcraft_project::LayerSource::Comp { item } = &l.source
+                    && seen.insert(*item)
+                {
+                    todo.push((*item, l.layer_time(ct)));
+                }
+            }
+            // Up: the comps nesting this one.
+            for iid in self.project.items.keys() {
+                if let Some(pc) = self.project.comp(*iid)
+                    && let Some(l) = pc.layers.iter().find(|l| matches!(&l.source, effectcraft_project::LayerSource::Comp { item } if *item == cid))
+                    && seen.insert(*iid)
+                {
+                    todo.push((*iid, l.comp_time(ct)));
+                }
+            }
+        }
+        for (cid, ct) in found {
+            if let Some(c) = self.project.comp(cid) {
+                let ct = c.frame_rate.snap_nearest(ct.clamp(Tick::ZERO, (c.duration - c.frame_duration()).max(Tick::ZERO)));
+                self.state.times.insert(cid, ct);
+            }
+        }
+    }
+
+    /// Make `id` the active comp, parking the previous comp's selection and restoring this one's.
+    pub fn activate_comp(&mut self, id: ItemId) {
+        if self.project.comp(id).is_none() || self.state.active_comp == Some(id) {
+            return;
+        }
+        self.remember_selection();
+        self.state.active_comp = Some(id);
+        self.recall_selection(id);
+        self.state.current_track = None;
+        // A text-edit session belongs to the comp that owned it. Switching comps ends it; even
+        // a same-numbered layer in the new comp must not inherit the old IME composition.
+        self.state.text_edit = None;
+    }
+
+    /// Leave no comp active, keeping the one that was active in [`EditorState::comp_selections`].
+    pub fn activate_comp_none(&mut self) {
+        self.remember_selection();
+        self.state.active_comp = None;
+        self.clear_live_selection();
+        self.state.current_track = None;
+        self.state.text_edit = None;
+    }
+
+    fn remember_selection(&mut self) {
+        let Some(id) = self.state.active_comp else { return };
+        let sel = CompSelection {
+            layers: self.state.selected_layers.clone(),
+            props: self.state.selected_props.clone(),
+            keys: self.state.selected_keys.clone(),
+            vertices: self.state.selected_vertices.clone(),
+        };
+        if sel.is_empty() {
+            self.state.comp_selections.remove(&id);
+        } else {
+            self.state.comp_selections.insert(id, sel);
+        }
+    }
+
+    fn recall_selection(&mut self, id: ItemId) {
+        match self.state.comp_selections.remove(&id) {
+            Some(sel) => {
+                self.state.selected_layers = sel.layers;
+                self.state.selected_props = sel.props;
+                self.state.selected_keys = sel.keys;
+                self.state.selected_vertices = sel.vertices;
+            }
+            None => self.clear_live_selection(),
+        }
+    }
+
+    fn clear_live_selection(&mut self) {
+        self.state.selected_layers.clear();
+        self.state.selected_props.clear();
+        self.state.selected_keys.clear();
+        self.state.selected_vertices.clear();
+    }
+
+    /// Open a comp in the viewer/timeline and make it active.
+    pub fn open_comp(&mut self, id: ItemId) {
+        if self.project.comp(id).is_none() {
+            return;
+        }
+        if !self.state.open_comps.contains(&id) {
+            self.state.open_comps.push(id);
+        }
+        if self.state.active_comp != Some(id) {
+            let previous = self.state.active_comp;
+            self.state.recent_comps.retain(|c| *c != id && Some(*c) != previous);
+            if let Some(previous) = previous {
+                self.state.recent_comps.insert(0, previous);
+                self.state.recent_comps.truncate(32);
+            }
+        }
+        self.activate_comp(id);
+        self.events.push(Event::OpenComp(id));
+    }
+
+    /// The open compositions and their current times, as a project file records them
+    /// ([`effectcraft_project::SavedView`]).
+    pub fn saved_view(&self) -> effectcraft_project::SavedView {
+        let comp_times = self.state.times.iter().filter(|(id, _)| self.project.comp(**id).is_some()).map(|(id, t)| (*id, *t)).collect();
+        effectcraft_project::SavedView { active_comp: self.state.active_comp, open_comps: self.state.open_comps.clone(), comp_times }
+    }
+
+    /// Reopen the compositions a project file was saved with (#748), each at its saved current
+    /// time (#1714). Ids that no longer name a comp are skipped; with none left the project stays
+    /// on the comp [`Session::replace_project`] opened (its first), as files from before the view
+    /// was saved do.
+    pub fn restore_view(&mut self, view: &effectcraft_project::SavedView) {
+        for (id, t) in &view.comp_times {
+            if let Some(comp) = self.project.comp(*id) {
+                let t = comp_frame_at(comp, *t);
+                self.state.times.insert(*id, t);
+            }
+        }
+        let mut open: Vec<ItemId> = Vec::new();
+        for id in view.open_comps.iter().copied().filter(|id| self.project.comp(*id).is_some()) {
+            if !open.contains(&id) {
+                open.push(id);
+            }
+        }
+        let Some(active) = view.active_comp.filter(|id| self.project.comp(*id).is_some()).or_else(|| open.first().copied()) else { return };
+        self.state.open_comps = open;
+        self.open_comp(active);
+    }
+
+    pub fn toast(&mut self, msg: impl Into<String>) {
+        self.events.push(Event::Toast { message: msg.into(), error: false });
+    }
+
+    pub fn drain_events(&mut self) -> Vec<Event> {
+        std::mem::take(&mut self.events)
+    }
+
+    /// The 3D view camera of a comp's viewer (None = the active camera).
+    pub fn view_camera(&self, comp: ItemId) -> Option<effectcraft_render::three_d::CameraState> {
+        let c = self.project.comp(comp)?;
+        if !c.has_3d() {
+            return None;
+        }
+        self.state.views3d.get(&comp)?.override_camera(c.width as f64, c.height as f64)
+    }
+
+    /// Render a comp frame with the session's footage + expression hosts.
+    pub fn render(&self, comp: ItemId, t: Tick, opts: RenderOpts) -> Image {
+        self.renderer(opts).comp_frame(comp, t)
+    }
+
+    /// The renderer [`Session::render`] uses: the session's footage, expressions, layer cache and
+    /// accelerator, and the render prefs (nested switches, draft shadows) over `opts`.
+    pub fn renderer(&self, opts: RenderOpts) -> Renderer<'_> {
+        let opts = RenderOpts { nested_switches: self.prefs.general.switches_affect_nested_comps, draft_shadows: self.prefs.three_d.realtime_shadows, ..opts };
+        let mut r = Renderer::new(&self.project, self.footage.as_ref(), opts);
+        r.expr = self.expr.as_deref();
+        r.cache = Some(&self.layer_cache);
+        r.accel = self.accel.as_deref();
+        r
+    }
+
+    /// Resolve a comp reference (item id number or name; `None`/null = the active comp).
+    pub fn resolve_comp(&self, comp: Option<&Value>) -> Result<ItemId> {
+        let p = match comp {
+            Some(v) if !v.is_null() => serde_json::json!({ "comp": v }),
+            _ => serde_json::json!({}),
+        };
+        commands::comp_id(self, &p)
+    }
+
+    /// Render a comp frame (comp time `t`) as opaque 8-bit RGBA over the comp background, scaled
+    /// so the longest side is at most `max_side` pixels (0 = full size). Returns (width, height, rgba).
+    pub fn render_rgba8(&self, comp: ItemId, t: Tick, max_side: u32) -> Result<(u32, u32, Vec<u8>)> {
+        let c = self.project.comp(comp).ok_or(EngineError::NoComp)?;
+        let long = c.width.max(c.height).max(1) as f64;
+        let scale = if max_side == 0 { 1.0 } else { (max_side as f64 / long).min(1.0) };
+        let img = self.render(comp, t, RenderOpts { scale, backend: effectcraft_render::Backend::Auto, ..Default::default() });
+        Ok((img.width, img.height, img.to_rgba8_over(c.background)))
+    }
+
+    /// A Project panel thumbnail of an item (a comp at `t`, footage at its first frame), longest
+    /// side at most `max_side`, as a job that owns everything it reads: frontends run it off the
+    /// UI thread (a big comp takes far longer than a frame). `None` for items without pixels.
+    pub fn thumbnail_job(&self, item: ItemId, t: Tick, max_side: u32) -> Option<ThumbnailJob> {
+        let it = self.project.item(item)?;
+        let footage = self.footage.clone();
+        match &it.kind {
+            effectcraft_project::ItemKind::Comp(c) => {
+                let (project, expr, cache) = (self.project.clone(), self.expr.clone(), self.layer_cache.clone());
+                let long = c.width.max(c.height).max(1) as f64;
+                let scale = if max_side == 0 { 1.0 } else { (max_side as f64 / long).min(1.0) };
+                let opts = RenderOpts {
+                    scale,
+                    nested_switches: self.prefs.general.switches_affect_nested_comps,
+                    draft_shadows: self.prefs.three_d.realtime_shadows,
+                    ..Default::default()
+                };
+                let bg = c.background;
+                Some(Box::new(move || {
+                    let mut r = Renderer::new(&project, footage.as_ref(), opts);
+                    r.expr = expr.as_deref();
+                    r.cache = Some(&cache);
+                    let img = r.comp_frame(item, t);
+                    Some((img.width, img.height, img.to_rgba8_over(bg)))
+                }))
+            }
+            effectcraft_project::ItemKind::Footage(f) if f.has_video => {
+                let f = f.clone();
+                Some(Box::new(move || {
+                    let img = footage.frame(item, &f, Tick(0))?;
+                    // Point-sample down to at most `max_side` on the long side.
+                    let step = (img.width.max(img.height) as f32 / max_side.max(1) as f32).ceil().max(1.0) as u32;
+                    let (w, h) = (img.width.div_ceil(step), img.height.div_ceil(step));
+                    let full = img.to_rgba8();
+                    let mut px = Vec::with_capacity((w * h * 4) as usize);
+                    for y in 0..h {
+                        for x in 0..w {
+                            let i = (((y * step) * img.width + x * step) * 4) as usize;
+                            px.extend_from_slice(&full[i..i + 4]);
+                        }
+                    }
+                    Some((w, h, px))
+                }))
+            }
+            _ => None,
+        }
+    }
+
+    /// [`Session::render_rgba8`], or with `transparent` the frame's own straight alpha (what a
+    /// render with RGB + Alpha channels writes) instead of compositing over the background.
+    pub fn render_rgba8_alpha(&self, comp: ItemId, t: Tick, max_side: u32, transparent: bool) -> Result<(u32, u32, Vec<u8>)> {
+        if !transparent {
+            return self.render_rgba8(comp, t, max_side);
+        }
+        let c = self.project.comp(comp).ok_or(EngineError::NoComp)?;
+        let long = c.width.max(c.height).max(1) as f64;
+        let scale = if max_side == 0 { 1.0 } else { (max_side as f64 / long).min(1.0) };
+        let img = self.render(comp, t, RenderOpts { scale, backend: effectcraft_render::Backend::Auto, ..Default::default() });
+        Ok((img.width, img.height, img.to_rgba8()))
+    }
+
+    /// Make the media layer and the layer cache let go of what they decoded from `footage`'s
+    /// files (it keys frames by path, so an overwritten file would keep showing its old pixels).
+    pub(crate) fn forget_decoded(&self, footage: &effectcraft_project::Footage) {
+        for p in std::iter::once(&footage.path).chain(&footage.sequence) {
+            self.footage.forget(p);
+        }
+        self.layer_cache.clear();
+    }
+
+    /// Replace the whole project (open/new), resetting history and state.
+    pub fn replace_project(&mut self, mut p: Project, path: Option<String>) {
+        if self.stop_render()
+            && let Some(mut job) = self.render_job.take()
+        {
+            // Let the worker notice the cancel; its updates refer to the old project.
+            job.wait();
+        }
+        self.render_job = None;
+        self.stored_paths = Default::default();
+        self.stop_track();
+        self.track_job = None;
+        self.stop_mask_track();
+        self.mask_job = None;
+        self.stop_warp();
+        self.warp_job = None;
+        self.warp_pending.clear();
+        self.stop_camera();
+        self.camera_job = None;
+        self.camera_pending.clear();
+        self.stop_roto();
+        self.roto_job = None;
+        self.roto_pending.clear();
+        self.drop_tasks();
+        self.script_ui.project_epoch = self.script_ui.project_epoch.wrapping_add(1);
+        p.fix_next_id();
+        upgrade_effects(&mut p);
+        // The media layer keys decoded frames by path: files of the new project may have changed
+        // since an earlier project decoded them (#1070).
+        for it in p.items.values() {
+            if let effectcraft_project::ItemKind::Footage(f) = &it.kind {
+                self.forget_decoded(f);
+            }
+        }
+        self.layer_cache.clear();
+        self.project = Arc::new(p);
+        // Its files may have changed since they were last stamped.
+        self.disk_salt = None;
+        self.history = History::default();
+        self.state = EditorState { snapping: true, view_layout: 1, ..Default::default() };
+        self.path = path;
+        self.bump();
+        self.mark_saved();
+        let first = self.project.comps().next().map(|(id, _)| *id);
+        if let Some(c) = first {
+            self.open_comp(c);
+        }
+    }
+}
+
+/// Bring effect instances saved by earlier versions up to date with the effect registry
+/// (renamed / regrouped / added parameters, reordered popups; see
+/// [`effectcraft_effects::migrate`]), and a project from before
+/// [`effectcraft_project::SCHEMA_EFFECT_SPACE`] into effect space
+/// ([`effectcraft_effects::migrate::to_effect_space`]). Stamps the current schema.
+pub fn upgrade_effects(p: &mut Project) {
+    let to_effect_space = p.schema < effectcraft_project::SCHEMA_EFFECT_SPACE;
+    // Effect bounds per layer: (size, top-left in layer coordinates).
+    let mut bounds = std::collections::HashMap::new();
+    for (cid, c) in p.comps() {
+        for l in &c.layers {
+            bounds.insert((*cid, l.id), effectcraft_render::effect_bounds(p, c, l));
+        }
+    }
+    let mut next = p.next_id;
+    for (cid, it) in p.items.iter_mut() {
+        let effectcraft_project::ItemKind::Comp(c) = &mut it.kind else { continue };
+        for l in &mut std::sync::Arc::make_mut(c).layers {
+            let (size, origin) = bounds.get(&(*cid, l.id)).copied().unwrap_or(([100.0, 100.0], [0.0; 2]));
+            // Effect space starts at the bounds' top-left: positions move by minus that corner.
+            // Adjustment layers run their effects on the comp below as it is: nothing moves.
+            let shift = |o: [f64; 2]| [-o[0], -o[1]];
+            let d = if l.switches.adjustment { [0.0; 2] } else { shift(origin) };
+            let clone_d = |src: Option<u64>| match src {
+                Some(id) => bounds.get(&(*cid, effectcraft_project::LayerId(id))).map_or([0.0; 2], |b| shift(b.1)),
+                None => d,
+            };
+            let Some(fx) = l.props.sub_mut("effects") else { continue };
+            for n in &mut fx.children {
+                let effectcraft_project::Node::Group(g) = n else { continue };
+                let effectcraft_project::GroupKind::Effect { effect } = &g.kind else { continue };
+                if let Some(spec) = effectcraft_effects::find(effect) {
+                    effectcraft_effects::migrate::upgrade_instance(spec, g, &mut effectcraft_project::build::Ids(&mut next), size);
+                    if to_effect_space {
+                        effectcraft_effects::migrate::to_effect_space(spec, g, size, d, &clone_d);
+                    }
+                }
+            }
+        }
+    }
+    p.next_id = next;
+    p.schema = effectcraft_project::SCHEMA_VERSION;
+}