effectcraft/docs/control-protocol.md

# Control protocol

The desktop app exposes a control channel for agents, tests and the MCP bridge:

```sh
effectcraft --control 9877        # or EFFECTCRAFT_CONTROL_PORT=9877
```

The port must be a number from 1 to 65535, and `--control` overrides the variable. A bad port or an
unknown option prints an error and the app exits with status 1 before it opens a window.

- **Transport:** TCP on `127.0.0.1` only, one JSON object per line in each direction. Connections are
  persistent; requests on one connection are answered in order.
- **Request:** `{"id": 1, "method": "engine.execute", "params": {...}}` (`id` is echoed back, `params`
  defaults to `{}`).
- **Reply:** `{"id": 1, "ok": true, "result": ...}` or `{"id": 1, "ok": false, "error": "message"}`.
- Requests run on the UI thread between frames. Input methods (`ui.click`, `ui.key` and similar)
  reply after the synthetic input has been processed. Methods that need an element that isn't drawn
  yet are retried for a few frames. A request times out after 60 s.
- **Only requests are read:** every line must be a JSON object with a string `method` (blank lines are
  skipped). Anything else (text that isn't JSON, a JSON array or number, an object without `method`,
  invalid UTF-8, a line longer than 4 MiB) gets one error reply ending in "closing the connection", and
  the server closes the connection, so nothing sent after it runs. An HTTP request (for example a web
  page's cross-origin `fetch` to `127.0.0.1:<port>`) therefore can't smuggle a command in its body: its
  request line is rejected first. At most 16 connections are served at once; further ones get an error
  line and are closed. The port has no authentication, so only enable it while you use it.

Quick test:

```sh
printf '{"id":1,"method":"engine.execute","params":{"command":"comp.new","params":{"name":"A"}}}\n' | nc 127.0.0.1 9877
```

## Engine

| Method | Params | Result |
|---|---|---|
| `engine.execute` | `{command, params?}` | The command's result. Every engine command (`effectcraft-cli commands`) runs exactly as it does headless, so it never opens a dialog: `comp.new {}` creates a default comp. UI-only ids (`tool.*`, `view.*`, `window.*`, `playback.*`, `timeline.*`, `app.*`) fall through to the menu dispatcher. Unknown top-level params are rejected, and the error lists the accepted keys. |
| `ui.menu.invoke` | `{id, params?}` | Like a menu click: commands with empty params may open their dialog (New Composition, Solid Settings, file pickers). |
| UI commands (via either) | | `timeline.column {column, visible?}` (av, keys, label, num, comment, switches, modes, parent, in, out, duration, stretch), `timeline.sourceName {value?}`, `timeline.search {query}`, `timeline.reveal.<kind>` / `timeline.revealAdd.<kind>` (the property shortcuts and Shift+shortcut: position, scale, rotation, opacity, anchor, effects, masks, feather, levels, animated, and the double-press sets maskPath, maskOpacity, timeRemap, expressions, material, paint, selected, missingEffects, waveform), `timeline.keyAt.<anchor\|position\|scale\|rotation\|opacity>` (Alt+Shift+A/P/S/R/T), `timeline.twirlSelected` (Ctrl/Cmd+`), `timeline.collapseAll`, `flowchart.options {layers?, effects?, solids?, direction?: lr\|tb, comp?}`, `flowchart.graph {comp?}` → `{nodes, edges}`, `window.workspace {name}` (all After Effects workspaces). |
| `engine.commands` | `{filter?, enabledOnly?}` | `[{id, label, menu, shortcut, params, enabled, why}]` |
| `ui.menu.list` | `{}` | The menu tree with enablement. |
| `render.frame` | `{comp?, time?, max_side?, path?, base64?}` | Renders a comp frame through the session, independent of the viewer zoom or resolution. `comp` is an id or name (default: the active comp), `time` is in comp seconds (default: the CTI), `max_side` caps the longest side (0 = full size). Writes a PNG to `path` (default: a temp file) and returns `{comp, time, width, height, path}`. With `base64: true` it returns `{…, png: "<base64>"}` and writes no file. |

Useful query commands for `engine.execute` (they aren't journaled or undoable): `project.summary`,
`comp.info {comp?}`, `layer.tree {layer, comp?, depth?, time?}` (every node has a `path`),
`prop.get {layer, path, comp?, time?}`, `editor.state`, `command.list {filter?, enabledOnly?, schemas?}`,
`command.describe {command}` (params doc and JSON Schema), `app.capabilities` (version, counts,
export formats, parity summary), `jobs.list` (Progress panel jobs, e.g. the background
`footage.check` after File ▸ Open).

Every engine command is reachable through `engine.execute`, and every interactive widget of every
panel registers an element id; both are enforced by `crates/ui-egui/tests/ui_agent_audit.rs`.

## UI state

| Method | Params | Result |
|---|---|---|
| `ui.inspect` | `{}` | Window size, pixels per point, fps, serialized `UiState`, playback, time, active comp, selection, open dialog, last render ms, `keyboardFocus`, `windowFocused`, `workspaceStorageError`. |
| `ui.elements` | `{prefix?}` | `[{id, label, rect: [x, y, w, h]}]`: the widgets drawn in the last frame, in points. |
| `ui.set` | `{tool?, workspace?, theme?, focused?, viewer?, timeline?, menuBar?, home?}` | `viewer: {zoom (null = fit), res: Full\|Half\|Third\|Quarter\|Auto, pan: [x,y], grid, rulers, safeMargins, transparencyGrid}`; `timeline: {pps (null = fit), start, graphEditor, showModes, openLayers: [ids], openGroups: [uids]}`. |
| `ui.panel.show` / `ui.panel.close` | `{panel}` | Panels: `Project`, `Composition`, `Timeline`, `EffectControls`, `EffectsPresets`, `Info`, `Preview`, `Character`, `Paragraph`, `Align` and others. |
| `ui.playback` | `{action: play\|stop\|toggle\|status}` | `{playing, time, audio, levelsDb, peaksDb}` (audio: an audio preview is running; L/R meter levels and held peaks in dBFS) |
| `ui.resize` | `{width, height}` | Resizes the window (points). |
| `ui.focus` | `{}` | Activates the window and takes keyboard focus. Agents normally avoid this, because the app is started without stealing focus. |
| `app.quit` | `{force?}` | Closes the app. A modified project shows the Save / Don't Save / Cancel prompt first (automation ids `dialog.unsaved.save`, `dialog.unsaved.dontSave`, `dialog.unsaved.cancel`) unless `force: true`. |

`keyboardFocus` is `null` when no egui widget has keyboard focus. Otherwise it contains the
actual widget `id` (hexadecimal), its `rect: [x, y, w, h]` when available, an `automationId`
when the widget registered its response identity, and `registryCandidates` containing exact
rectangle matches. Candidates alone do not establish widget identity. Header, toolbar and
dock-tab controls register their response identity. `ui.focused` continues to identify the
focused panel; it is separate from keyboard widget focus. `windowFocused` reports the native
window focus received by egui, which can differ from the retained widget focus.

When a configuration store is available, current dock and floating geometry, focused and
maximized panels, and named workspace snapshots persist in `workspaces.json`. The current
layout and named snapshots are independent: changing a divider does not overwrite the named
snapshot until `window.saveWorkspace` runs. Changes save after pointer release, at most once
per second, with a final save on normal exit. Version 1 files are limited to 1 MiB and bounded
workspace trees; extra viewer IDs must be between 1 and 65,535. Native reads enforce the size
limit while reading and report I/O and UTF-8
errors. Unreadable, invalid or newer files leave the default workspace available and are
preserved for the entire session, including after later layout changes. Load and save errors
appear in the status message and the nullable
`workspaceStorageError` field; a failed write remains eligible for retry.
`window.saveWorkspace`, `window.saveWorkspaceAs` and `window.editWorkspaces` (rename, delete)
write the file immediately. Through `ui.menu.invoke` they return an error when it isn't written
(a failed write, a file preserved after a failed load, or no configuration store);
`engine.execute` hands them to the UI and returns `{frontend}` first, so check
`workspaceStorageError` there. The changed workspaces still apply for the session, and a later
save retries them.

## Input

Points are logical window coordinates. A target is `{id}` (the element's centre; add `fx`/`fy` between
0 and 1 to pick a spot inside it) or `{x, y}`. `modifiers` is `{shift, alt, command, ctrl}`, where
`command` is ⌘ on macOS and Ctrl elsewhere.

| Method | Params |
|---|---|
| `ui.click` | `{id \| x,y, button?: left\|right\|middle, count?, modifiers?}` |
| `ui.move` | `{id \| x,y}` |
| `ui.drag` | `{from: target, to: target, steps? (12), modifiers?}`: press, move, release |
| `ui.scroll` | `{id \| x,y, dx, dy}` |
| `ui.key` | `{key}`, for example `Space`, `F9`, `Cmd+Z`, `Cmd+Shift+Z`, `PageDown`, `Escape` |
| `ui.type` | `{text}`: text input into the focused field |

Shortcut presets also accept `Physical+<shortcut>` for a keyboard position, using egui's
US-position names (for example `Physical+6` and `Physical+Minus` distinguish AZERTY's
`-` and `)` keys). Physical bindings take precedence over logical bindings for that key
press. `ui.key` accepts the same notation to test them. Ordinary shortcuts remain layout-aware.
`time.workAreaStart` and `time.workAreaEnd` navigate to the first and last included work-area
frames and can be assigned through `shortcuts.set`.

## Locating things

| Method | Params | Result |
|---|---|---|
| `ui.viewer.locate` | `{x, y}` (comp pixels) | `{x, y}` window point |
| `ui.viewer.hit` | `{id \| x,y}` (window point) | `{x, y}` comp pixel |
| `ui.timeline.locate` | `{layer (id), time?}` | `{x, y}` window point on the layer bar |

## Screenshots

| Method | Params | Result |
|---|---|---|
| `ui.screenshot` | `{path?, panel?, id?}` | `{path, width, height}`: a PNG of the window, or cropped to one panel or element. |

Element ids are stable, for example `tools.Selection`, `panel.Timeline`, `panel.tab.EffectControls`,
`panel.tab.Timeline.<comp>` (one Timeline tab per open comp; `panel.tab.Timeline` is the shown
one), `panel.tab.Viewer(<n>)` and `viewers.<n>` (View ▸ New Viewer's other Composition viewers;
`viewers.0` is the Composition panel while another viewer is active), `header.workspace.Animation`, `project.item.<id>` (a double-click opens the item, Enter
renames it), `viewer.comp`, `viewer.handle.<layer>.<i>`,
`timeline.layer.<id>.bar`, `timeline.layer.<id>.nestedMarker.<i>` (a precomp's comp markers), `timeline.layer.<id>.twirl`, `timeline.layer.<id>.row` (click selects,
Enter or a double-click renames, drag reorders), `timeline.prop.<uid>.stopwatch`,
`timeline.key.<uid>.<frame>` (and `timeline.keyAt.<uid>.<ticks>`, exact in layer-time ticks, for
keys on subframes), `timeline.cti`, `effectControls.prop.<uid>.value` (an angle's
revolutions are `timeline.prop.<uid>.revolutions`, `effectControls.prop.<uid>.revolutions` and
`properties.prop.<uid>.revolutions`) and `effects.item.<name>`. The Composition viewer adds `viewer.magnification`, `viewer.resolution`,
`viewer.roi`, `viewer.grid`, `viewer.channel`, `viewer.exposure`, `viewer.snapshot`,
`viewer.showSnapshot`, `viewer.fastPreviews` (their popup entries are `viewer.<menu>Item.<n>`),
`viewer.ruler.top|left|origin`, `viewer.mask.<uid>.vertex.<i>`, `viewer.shapePath.<uid>.vertex.<i>`,
`viewer.motionPath.<layer>.<key>[.in|.out]`, `viewer.puppetPin.<uid>[.rotate|.scale]`,
`viewer.freeTransform.handle.<i>` and
`viewer.regionOfInterest`; the Graph Editor adds `timeline.graph.transformBox[.<i>]`,
`timeline.graph.snap` and `timeline.graph.reference`. Use `ui.elements` to see what is on screen.

Viewer state that agents drive headless too: `view.snapping`, `view.snappingOptions
{edgesExtended?, collapsedFeatures?, toggle?}` (the Tools bar's Snapping options,
`header.snappingOptions`: After Effects' Snap Edges Extended and Snap to Features in Collapsed
Compositions and Text Layers), `view.channel {channel, colorized?}`,
`view.exposure {stops | delta}`, `view.resetExposure`, `view.takeSnapshot`, `view.showSnapshot`,
`view.fastPreviewMode {mode}` (one mode each, for shortcuts:
`view.fastPreviews.off|adaptive|draft|fastDraft|wireframe`, and for the channels
`view.channel.red|green|blue|alpha|redColorized|greenColorized|blueColorized|rgbStraight`), `view.res.full|half|third|quarter|auto {comp?}` and
`view.res.custom {factor, comp?}` (the comp's Resolution, saved with the project but no undo
step; `ui.set {viewer: {res}}` sets the active comp's, and `ui.inspect` reports it as
`ui.viewer.res`), `view.setRegionOfInterest {rect}`, `view.addGuide {percent?}`,
`view.addPercentGuide`, `view.convertGuides {to: percent|pixels, index?}`,
`view.moveGuide` (comp pixels, whatever the guide's unit), `view.removeGuide`, `effect.setLabel {layer?, effect, label}`; editing: `shape.newPath` (Pen on shape layers),
`shape.newShape` (the shape tools: a new group in the selected shape layer, else a new shape layer),
`shape.toolOptions` (the Tools bar's Tool Creates Shape / Mask and Fill and Stroke Options),
`mask.insertVertex`, `mask.convertVertex`, `mask.deleteVertices`, `path.freeTransform` (masks and
shape paths by uid), `keys.setSpatialTangents` (motion-path handles) and `keys.transform` (Graph
Editor transform box, timeline Alt-drag scaling).

The MCP server's bridge mode (`effectcraft-cli mcp --bridge 9877`) is a thin client of this protocol;
see [agents.md](agents.md).

Keyframe command times (`prop.set`, `prop.addKey`, `keys.set`, `keys.select`) default to layer
seconds. Set `timeBase: "comp"` for comp seconds; `keys.set.newTime` and every
`keys.select.keys[].time` use the same input base. Omitted `prop.set` or `prop.addKey` times use
the target comp's CTI. Supplied write times snap to its nearest comp frame before conversion
to stored layer time, including on stretched or reversed layers. Existing `keys.set` neighbor
constraints and roving adjustment can change the final stored time.

Explicit bases add `layerTime` and `compTime` to unsplit `prop.set` and `prop.addKey` replies,
alongside `value` or `count`. Separated Position `prop.set` keeps an array of per-axis replies.
Explicit `keys.select` replies contain `count` and `keys[]`, with timing on each key in the
resulting selection. Key metadata's `time` remains layer seconds regardless of the input base.
Without `timeBase`, these three commands retain their existing JSON value/count replies,
including outside the layer's `[in, out)` range. Timing metadata carries outside-range warnings;
`keys.set` and `prop.get.keys[]` report both bases and warnings without an explicit base too.
`prop.get.time` is comp seconds. For these commands, `path` or `prop` identifies a property, not a group.
Set a layer's offset with `layer.timing {layer, start}` (comp seconds).

Panel moves, tab ordering, edge splits and floating geometry use shared docking transactions.
`window.floatPanel` requires exactly four finite numbers when `rect` is supplied. Invalid
geometry or missing source/anchor panels leaves the layout unchanged. The persisted workspace
shape is unchanged: accordion open states and explicit heights, floating groups, and dynamic
viewer/ScriptUI identities remain app data. Pointer drops use the same shared placement rules
as commands, with floating groups resolved in their actual window stacking order.

`window.dockAction` accepts `{action}` using the shared docking action's JSON form. It
covers tab moves and ordering, split and floating geometry, activation, and closing.
For example, `{"action":{"ResizeSplit":{"path":[],"size":{"FixedFirst":360}}}}`
resizes the root split; path entries use `false` for the first child and `true` for
the second. `{"action":{"MoveFloating":{"panel":"Info","rect":[45,65,420,320]}}}`
repositions and resizes the floating group containing Info. Invalid actions leave the
layout unchanged. Pointer gestures dispatch through this same catalog command.
EffectCraft also supports `SetStackOpen` and `ResizeStack`. Dynamic panel identities use
`{"Viewer":42}` or `{"ScriptPanel":77}` in the action. Closing runs the existing viewer
and ScriptUI lifecycle callbacks; opening uses the existing panel creation commands.