Files
element-call-Github/sdk/SdkMigration.md
T
Timo K. 5c6d2f0891 Update SDK to be consumed by Element Call's CallViewModel
Update the public API to export the primitives and operators the call
model needs, and change `LocalMediaInputs` from observable flags to
immediate booleans with imperative setters. Add session timings, media
quality and capture settings as configuration options, and allow the
host to override the transport discovery with explicit URLs.
2026-10-08 13:53:56 +02:00

340 lines
34 KiB
Markdown

# From `CallViewModel` to `MatrixRTCClient`
How Element Call gets from today's `CallViewModel`, which does everything, to a
view model that consumes the SDK. The target shape is in
[`SdkArchitecture.md`](./SdkArchitecture.md); this document is the inventory of
what moves, what stays, and how far along it is. It refers to source files and
symbols, so it ages with the code; the architecture document should not.
## Status
| Slice | State |
| ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------- |
| 1. Scaffold: `sdk/` packaging, the interface, the harness, the smoke test | done, October 2026 |
| 2. First implementation of `createMatrixRTCClient` under `sdk/src`, the media adapter, the e2e suite | done, 1 October 2026 |
| 3. Copy the shared modules into `sdk/src/` with their tests, drop every `src/` import, turn on the import boundary | done, 2 October 2026 |
| 4. `createCallViewModel$` consumes the client; media view models take `media$`; Element Call imports the primitives and enums from the SDK and deletes its own copies; the old demo target is removed | done, 2 October 2026 |
Element Call now consumes the SDK. `InCallView` creates the client from the
configuration, settings and URL parameters, and hands it to `createCallViewModel$`,
which keeps what makes the session a call. The modules below were deleted from
`src/` once the SDK had its copies, and `Behavior`, `ObservableScope`, the
observable operators, `E2eeType`, `EncryptionSystem` and `MatrixRTCMode` are
re-exported from the SDK by their old paths so the rest of Element Call did not
have to change in the same step. The view model tests drive a fake
`MatrixRTCClient` (`mockMatrixRTCClient` in `src/utils/test.ts`) instead of mocked
LiveKit rooms; the tests of the deleted modules live on in `sdk/src`.
## What was copied from `src/`, and what changed on the way
All of these are gone from `src/` as of slice 4; the table records where they went.
Each module came with its tests (`sdk/src/utils/test.ts` and `test-fixtures.ts` are
the subset of `src/utils/test.ts` and `test-fixtures.ts` they need). In slice 4
Element Call switches to the SDK's copy and deletes its own.
| In `src/` | In `sdk/src/` | What changed |
| ----------------------------------------------------------------------------------- | --------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------- |
| `state/Behavior.ts`, `state/ObservableScope.ts`, `utils/observable.ts` | `reactive/` | as is |
| `state/SessionBehaviors.ts` | `session/SessionBehaviors.ts` | as is |
| `state/CallViewModel/remoteMembers/Connection.ts` | `session/Connection.ts` | throws `MatrixRTCError`s; the SDK still subclasses it as `ResolvedConnection` to keep the JWT answer, to be folded in |
| `state/CallViewModel/remoteMembers/ConnectionFactory.ts` | `session/ConnectionFactory.ts` | the interface only; `ECConnectionFactory` reads settings and `MediaDevices`, the SDK has `LivekitConnectionFactory` |
| `state/CallViewModel/remoteMembers/ConnectionManager.ts` | `session/ConnectionManager.ts` | as is |
| `state/CallViewModel/remoteMembers/MatrixLivekitMembers.ts` | `session/MatrixLivekitMembers.ts` | as is; the SDK maps its result to `RTCMember`, `TaggedParticipant` is internal |
| `state/CallViewModel/remoteMembers/MatrixMemberMetadata.ts`, `utils/displayname.ts` | `session/MatrixMemberMetadata.ts`, `utils/displayname.ts` | as is |
| `state/CallViewModel/localMember/HomeserverConnected.ts` | `session/HomeserverConnected.ts` | the grace period defaults to `defaultSessionTimings` instead of `Config.get()` |
| `state/CallViewModel/localMember/LocalTransport.ts` | `session/LocalTransport.ts` | the type and `isLocalTransport`; discovery without the custom-url setting |
| `state/CallViewModel/localMember/RtcTransportAutoDiscovery.ts` | `session/RtcTransportAutoDiscovery.ts` | takes `fallbackTransportUrl` instead of a resolved config |
| `state/CallViewModel/localMember/LocalMember.ts` | `session/LocalMember.ts` | rewritten; only `observeSharingScreen$` was copied |
| `livekit/openIDSFU.ts` | `session/openIDSFU.ts` | the delegated leave timeout is a parameter (`delayTimeoutMs`) instead of `Config.get()` |
| `livekit/options.ts` | `session/livekitOptions.ts` | `buildLiveKitOptions(mediaQuality?)` only; `getLiveKitOptions` and the `Config` singleton are gone |
| `e2ee/matrixKeyProvider.ts` | `session/MatrixKeyProvider.ts` | as is |
| `e2ee/e2eeType.ts`, the `EncryptionSystem` type from `e2ee/sharedKeyManagement.ts` | `encryption.ts` | the React hooks stayed behind |
| `MatrixRTCMode`, the timings and media quality types from `config/ConfigOptions.ts` | `config.ts` | `defaultSessionTimings` and `defaultMediaQuality` replace `DEFAULT_CONFIG` |
| `utils/errors.ts` | `errors.ts` | `MatrixRTCError` with `code` and `category` replaces `ElementCallError`; messages are plain English, the host translates by code |
| `doNetworkOperationWithRetry` from `utils/matrix.ts` | `utils/network.ts` | as is |
Rewritten in the SDK rather than copied, because the originals read settings,
config, analytics or the host bridge: the local member (`session/LocalMember.ts`),
the publisher (`session/Publisher.ts`), the connection factory and LiveKit room
options (`session/ConnectionFactory.ts`), transport discovery
(`session/LocalTransport.ts`), the join (`session/joinJsSdkSession.ts`) and the
key provider selection (`session/KeyProvider.ts`).
## What becomes what in `createCallViewModel$`
Everything below `createCallViewModel$` that is not presentation and not in the
call-specific table of the architecture document. Grouped by what it is today in
`src/state/CallViewModel/CallViewModel.ts`.
| Binding today | In the SDK |
| ---------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------- |
| `livekitKeyProvider` via `getE2eeKeyProvider` | internal, keyed off `options.encryptionSystem` |
| `matrixRTCMode` resolution from `Config.get()` | an input; resolution stays in the caller |
| `matrixRTCSession` parameter | internal: the session manager for the slot, `getRoomSession(room)` |
| `memberships$`, `membershipsAndTransports` | internal; surfaces as `RTCMember.transport$` |
| `ownMembershipIdentity` | internal; surfaces as `RTCMember.id` |
| `localTransport$` via `getLocalTransport` | internal |
| `connectionFactory`, `connectionManager` | internal; surfaces as `connectedTransports$` |
| `remoteMatrixLivekitMembers$` | `remoteMembers$` |
| `localMembership` via `createLocalMembership$`, `enterRTCSession`, `Publisher`, `delayId$` | internal; surfaces as `join`, `leave`, `status$`, `connected$`, `reconnecting$`, the screen share fields |
| `localRtcMembership$`, `localMatrixLivekitMember$` | `localMember$` |
| `matrixLivekitMembers$`, `participantCount$` | `memberCount$` |
| `matrixRoomMembers$`, `matrixMemberMetadataStore` | `RTCMember.displayName$` / `avatarUrl$` |
| `allConnections$` | `connectedTransports$` |
| `livekitRoomItems$` | dropped; audio renders from `remoteMembers$[].media$` |
| `keyRotationSuppressed$` | same |
| `sharingScreen$`, `toggleScreenSharing` | `localMember$.sharingScreen$`, `.toggleScreenSharing` |
| `errors$` and the `fatalError$` mapping | `fatalError$`, as `MatrixRTCError` |
| `join`, `leave`, `connected$`, `reconnecting$`, `screenShareError$`, `dismissScreenShareError` | same names on `MatrixRTCClient` / `LocalRTCMember` |
| `callIntent` option, `updateCallIntent` from the camera | `applicationData["m.call.intent"]`; the camera sync is still in the SDK, see the open decisions |
Changes to the call sites that the rename brings: `localMember$` and
`remoteMembers$` replace `localMatrixLivekitMember$` and
`remoteMatrixLivekitMembers$`; `connection$` on a member goes away, since the view
model only ever used `livekitRoom` (for `waitingForMedia$` and encryption errors,
both on `MemberMedia` now) and `transport.livekit_service_url` (now
`transport$.id`); `connectedTransports$` replaces `allConnections$`, since the
developer panel only needed which transports exist and whether they are up.
## What stays in `CallViewModel`
Everything in the call-specific table, plus everything that takes `userMedia$` or a
UI input and turns it into something to draw:
- Media view models (`createWrappedUserMedia` and below), built from
`remoteMembers$` / `localMember$` instead of participants.
- `CallNotificationLifecycle.ts` in full: `ringAttempts$`, `autoLeave$`,
`ringingMedia$`, `ringingStatusLocation`.
- `leave$` (= `autoLeave$` + `hangup()` + `hostBridge.hangUp$`), `hangup()`.
- `screenShares$`.
- Sounds: `joinSoundEffect$`, `leaveSoundEffect$`, `newHandRaised$`,
`newScreenShare$`, `audibleReactions$`, `visibleReactions$`.
- `handsRaised$`, `reactions$`, until they move onto `RTCMember`.
- All layout: `spotlightSpeaker$`, `grid$`, `spotlight$`, `pip*`, `windowMode$`,
`layoutSwitchVm`, every `*LayoutMedia$`, `layout$`, `visibleTiles$`,
`tileStoreGeneration$`, `overflowing$`, `spotlightExpanded$`.
- Chrome: `showHeader$`, `showFooter$`, `edgeToEdge$`, `showModals$`,
`settingsOpen$`, `showSpotlightIndicators$`, `showSpeakingIndicators$`,
`showNameTags$`, tap and hover subjects.
- Audio routing: `earpieceMode$`, `audioOutputSwitcher$`, which read
`MediaDevices`.
- `CallViewModelOptions` keeps `hostBridge`, `controlledAudioDevices`, `header`,
`showControls`, `hideScreensharing`, `waitForCallPickup`,
`autoLeaveWhenOthersLeft`, `windowSize$`, `toggleScreensharing` (test override),
and forwards `encryptionSystem`, `matrixRTCMode`, `sendNotificationType` and
`applicationData` to `MatrixRTCClientOptions`.
## The media view models and the participant
The goal of slice 4 on the media side: nothing in Element Call imports
`Participant`, `RemoteParticipant`, `LocalParticipant`, `TrackPublication`,
`Track` or `TrackReference`. This is where the participant flows today, and what
each use becomes.
### Where the participant flows today
Start: `remoteMatrixLivekitMembers$` in `CallViewModel.ts`, built by
`createRemoteMatrixLivekitMembers$` in
`src/state/CallViewModel/remoteMembers/MatrixLivekitMembers.ts`, as
`participant: { type: "remote"; value$: Behavior<RemoteParticipant | null> }`.
Consumers, in order of depth:
1. `MatrixLivekitMembers.ts` matches `participant.identity` against
`membership.rtcBackendIdentity`; logs `participant.sid`.
2. `CallViewModel.ts` `livekitRoomItems$` reads `isLocal`, `identity`, hands
`connection.livekitRoom` plus identities to `LivekitRoomAudioRenderer`.
3. `CallViewModel.ts` `userMedia$` passes the whole `TaggedParticipant` into
`createWrappedUserMedia`.
4. `src/state/media/WrappedUserMediaViewModel.ts`: `observeParticipantEvents(p,
TrackPublished, TrackUnpublished, LocalTrackPublished, LocalTrackUnpublished)`
then `p.isScreenShareEnabled` to spawn screen share view models.
5. `src/state/media/UserMediaViewModel.ts`: `observeParticipantMedia(p)` for
`microphoneTrack?.isMuted` / `cameraTrack?.isMuted`; `IsSpeakingChanged` →
`p.isSpeaking`; `observeRtpStreamStats$(p, source, type)`.
6. `src/state/media/MemberMediaViewModel.ts`: `observeTrackReference$(p, source)`
for audio and video; `publication.isEncrypted`; `p.isLocal`; `p.identity`
matched inside `RoomEvent.EncryptionError` messages; inbound RTP frame counters.
7. `src/state/media/RemoteUserMediaViewModel.ts`, `RemoteScreenShareViewModel.ts`:
`p.setVolume(v)` / `p.setVolume(v, ScreenShareAudio)`; `participant === null`
means "waiting for media".
8. `src/state/observeTrackReference.ts`: `p.getTrackPublication(source)` wrapped as
`{ participant, publication, source }`.
9. `src/state/media/observeRtpStreamStats.ts`: `publication.track` must be
`RemoteTrack | LocalTrack`, then `track.getRTCStatsReport()`.
10. Views: `src/tile/MediaView.tsx` renders `<VideoTrack trackRef={video}>` from
`@livekit/components-react`; `src/livekit/MatrixAudioRenderer.tsx` uses
`useTracks` on the LiveKit room, filters on `ref.participant.isLocal` /
`.identity`, and calls `RemoteAudioTrack.setAudioContext` /
`setWebAudioPlugins`.
Local-only extras, same shape but on `LocalParticipant`
(`localMember/LocalMember.ts`, `Publisher.ts`,
`src/state/media/LocalUserMediaViewModel.ts`): `trackPublications`,
`audioTrackPublications`, `setScreenShareEnabled`, `setMicrophoneEnabled`,
`setCameraEnabled`, `enableCameraAndMicrophone`, `isMicrophoneEnabled`,
`isCameraEnabled`, `unpublishTrack`, and on the camera `LocalVideoTrack`:
`facingModeFromLocalTrack`, `restartTrack`, `mediaStreamTrack`,
`TrackEvent.Restarted` / `Muted`.
### Participant API actually used, and what covers it
| LiveKit surface | Used for | Used in | Now |
| --------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------- | ----------- | ------------------------------------------------ |
| `identity` | match to `rtcBackendIdentity`; audio renderer allow-list; E2EE error matching; logs | 1, 2, 6, 10 | matched inside the SDK; `RTCMember.id` |
| `sid` | logs only | 1 | SDK logs |
| `isLocal` | skip local audio; encryption status short-circuit | 2, 6, 10 | `MemberMedia.local` |
| `isSpeaking` + `IsSpeakingChanged` | `speaking$` | 5 | `MemberMedia.speaking$` |
| `isScreenShareEnabled` + publish events | spawn screen share VM | 4 | `MemberMedia.screenShareEnabled$` |
| `observeParticipantMedia(p)` → `microphoneTrack?.isMuted`, `cameraTrack?.isMuted` | `audioEnabled$`, `videoEnabled$` | 5 | `microphone$` / `camera$` → `muted$` |
| `getTrackPublication(source)` for the four sources | `TrackReference` for video, encryption, stats, screen share audio presence | 6, 7, 8 | the four track behaviors |
| `publication.isEncrypted` | `unencryptedWarning$` | 6 | `MediaTrack.encrypted$` |
| `publication.track.getRTCStatsReport()` | `audioStreamStats$`, `videoStreamStats$`, "receiving okay" heuristic | 5, 6, 9 | `MediaTrack.stats$` |
| `setVolume(v)`, `setVolume(v, ScreenShareAudio)` | `VolumeControls` sink | 7 | `AudioMediaTrack.setVolume` |
| `TrackReference` → `<VideoTrack>` | render video | 10 | `MediaTrack.attach` on a `<video>` |
| room `useTracks` + `RemoteAudioTrack.setAudioContext/setWebAudioPlugins` | render audio with earpiece pan/gain | 10 | one `<audio>` per audio track, `setAudioContext` |
| room `RoomEvent.EncryptionError` with `identity` + `"MissingKey"`/`"InvalidKey"` | `encryptionStatus$` | 6 | `MemberMedia.encryptionError$` |
Everything else in the media view models (`observeSpeaker$`, `VolumeControls`,
`SortingBin`, hand raise, reactions, display name, avatar, aspect ratio) already
works on plain booleans and observables and does not change.
### How the call sites map onto `MemberMedia`
- `audioEnabled$` = `microphone$ → track?.muted$ === false`; `videoEnabled$`
likewise from `camera$`.
- `unencryptedWarning$` = any of the four tracks with `encrypted$ === false`.
- `encryptionStatus$` = `encryptionError$` plus a "frames decoded" check on
`camera$.stats$` / `microphone$.stats$`; same logic, no participant.
- `screenShares$` in `WrappedUserMediaViewModel` keys off `screenShareEnabled$`.
- `VolumeControls` sink = `microphone$.value?.setVolume` /
`screenShareAudio$.value?.setVolume`.
- `waitingForMedia$` = transport present and `media === null`, unchanged
semantics; `TaggedParticipant` goes away.
- `video$: Behavior<TrackReference | undefined>` on `BaseMemberMediaViewModel`
becomes `Behavior<VideoMediaTrack | undefined>`; `MediaView` replaces
`<VideoTrack trackRef>` with a `<video>` plus `attach` / `detach` in an effect,
keeping the `onResize` callback for the aspect ratio. `VideoPreview.tsx` already
follows this pattern.
- `LivekitRoomAudioRenderer` stops using `useTracks` on the room and renders one
`<audio>` per `microphone$` / `screenShareAudio$` across `remoteMembers$`. That
removes the "no matching matrix call member" warning path, since an unmatched
track can no longer be seen.
- The `showConnectionStats` setting gates the subscription to `stats$` in the view
model; the SDK polls only while subscribed.
- Stories and tests mock `attach` by setting `srcObject` from
`canvas.captureStream()` on the element, or by doing nothing and asserting the
call.
## Packaging, as it was planned
`sdk/` mirrors `component/` file for file. The table that drove the scaffold, kept
for the record:
| `component/` | `sdk/` | Differences |
| ------------------------------------------------------------------------------------ | ----------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------- |
| `package.json` (`@element-hq/element-call-component`) | `package.json` (`@element-hq/matrixrtc-sdk`) | peers: `matrix-js-sdk`, `livekit-client`, `rxjs`. No React, no Compound. `exports`: `"."` only. No `./style.css`, no `sideEffects`. Same `prepare`. |
| `pnpm-workspace.yaml` (marker, `autoInstallPeers: false`) | same | none |
| `tsconfig.build.json` | same | `include: ["./index.ts"]` |
| `index.tsx` + `api.ts` | `index.ts` + `src/api.ts` | one entry; no separate types entry until a host asks |
| `host.ts`, `localization.ts`, `ElementCall.module.css`, `build/scopeStylesToRoot.ts` | none | no host bridge, no i18n, no styles |
| `dev/` on port 3001 | `dev/` on port 3002 via `vite-sdk-dev.config.ts` | plain DOM |
| `vite-component.config.ts` | `vite-sdk.config.ts` | `vitePluginsConfig({ mode, html: false })`, `outDir: "sdk/dist"`, externals = js-sdk and LiveKit entries plus `rxjs` |
| root scripts `build:component*` | `build:sdk*` | `build:sdk:types` = `tsc -p sdk/tsconfig.build.json` |
| root `tsconfig.json` `include` | adds `./sdk/**/*.ts` | |
| `scripts/check-component-externals.mjs` | parameterised by config; `sdk` added to the sources, `sdk/dev` excluded | |
| `knip.ts` | `vite-sdk.config.ts`, `vite-sdk-dev.config.ts`, `sdk/index.ts` as entry | |
| `vitest.config.ts` unit project | adds `sdk/**/*.test.ts` | |
| `package.json` `lint:oxlint` paths | adds `sdk` | |
Why not a pnpm workspace package yet: the root has no `packages:` in
`pnpm-workspace.yaml`, so a workspace split means restructuring the app, the
component's `prepare` trick, CI and the lockfile at the same time as moving the
code, and dev-time HMR across workspace packages needs the same source alias
anyway. It is the right end state if the SDK gets a release cadence of its own.
## Reference: the `CallViewModel` public API before the migration
Source: `src/state/CallViewModel/CallViewModel.ts`. Only consumer outside tests:
`src/room/InCallView.tsx`. A snapshot, so that the split can be checked against
what was there.
### Factory
`createCallViewModel$(scope, matrixRTCSession, matrixRoom, mediaDevices, muteStates, options, handsRaisedSubject$, reactionsSubject$, trackProcessorState$): CallViewModel`
- `scope: ObservableScope`: ending the scope is one of the two ways to leave.
- `matrixRTCSession: MatrixRTCSession`, `matrixRoom: MatrixRoom`: one room per view model.
- `mediaDevices: MediaDevices`, `muteStates: MuteStates`
- `options: CallViewModelOptions` (below)
- `handsRaisedSubject$: Observable<Record<string, RaisedHandInfo>>`
- `reactionsSubject$: Observable<Record<string, ReactionInfo>>`
- `trackProcessorState$: Behavior<ProcessorState>`
Helper: `callViewModelOptionsFromParams(params: UrlParams)` picks
`controlledAudioDevices`, `header`, `showControls`, `hideScreensharing`,
`sendNotificationType`, `callIntent` out of the URL params. `autoLeaveWhenOthersLeft`
and `waitForCallPickup` are left to the caller.
### `CallViewModelOptions`
| Field | Type | Note |
| ----------------------------------------------------------------------------------------------------------- | --------------------------- | --------------------------------------------------- |
| `encryptionSystem` | `EncryptionSystem` | required |
| `hostBridge?` | `HostBridge` | host can hang up / observe join+leave; default none |
| `controlledAudioDevices?` | `boolean` | host controls audio output devices |
| `header?` | `HeaderStyle` | default `Standard` |
| `showControls?` | `boolean` | default `true` |
| `hideScreensharing?` | `boolean` | default `false` |
| `sendNotificationType?` | `RTCNotificationType` | notification sent on join |
| `callIntent?` | `RTCCallIntent` | |
| `autoLeaveWhenOthersLeft?` | `boolean` | |
| `waitForCallPickup?` | `boolean` | telephone-style ringing UI |
| `windowSize$` | `Behavior<{width; height}>` | required; drives `WindowMode` |
| `matrixRTCMode?` | `MatrixRTCMode` | MatrixRTC version / compat mode |
| `livekitRoomFactory?`, `connectionState$?`, `localTransport?`, `connectionFactory?`, `toggleScreensharing?` | | test overrides |
### The interface, grouped
**Lifecycle / connection** (to the client): `join()`, `leave()`, `hangup()`,
`leave$: Observable<"user" | AutoLeaveReason>`, `autoLeave$`, `connected$`,
`reconnecting$`, `allConnections$: Behavior<ConnectionManagerData>`,
`fatalError$: Behavior<ElementCallError | null>`, `keyRotationSuppressed$`.
**Members / participants** (to the client): `participantCount$`,
`localMatrixLivekitMember$`, `remoteMatrixLivekitMembers$`, `livekitRoomItems$`,
`handsRaised$`, `reactions$` (keyed by `${userId}:${deviceId}`).
**Screen sharing** (capability to the client, error UI stays): `toggleScreenSharing`,
`sharingScreen$`, `screenShareError$`, `dismissScreenShareError()`.
**Ringing** (stays): `ringingVm$`, `ringingStatusLocation`.
**Audio routing** (stays): `earpieceMode$`, `audioOutputSwitcher$`.
**Sounds and transient events** (stay): `joinSoundEffect$`, `leaveSoundEffect$`,
`newHandRaised$`, `newScreenShare$`, `audibleReactions$`, `visibleReactions$`,
`MAX_PARTICIPANT_COUNT_FOR_SOUND = 8`, `THROTTLE_SOUND_EFFECT_MS = 500`.
**Layout and tiles** (stay): `layout$`, `tileStoreGeneration$`,
`showSpotlightIndicators$`, `showSpeakingIndicators$`, `showNameTags$`,
`spotlightExpanded$`, `toggleSpotlightExpanded$`, `layoutSwitchVm$`.
**Chrome visibility and UI interaction** (stay): `showHeader$`, `showFooter$`,
`edgeToEdge$`, `overflowing$`, `showModals$`, `settingsOpen$`, `setSettingsOpen$`,
`tapScreen()`, `tapControls()`, `hoverScreen()`, `unhoverScreen()`.
### Pending rename noted in the source
A TODO above `CallViewModelOptions` proposes: member/membership → `rtcMember`,
participant → `livekitParticipant`, matrixLivekitItem → `callMember`; and in the
js-sdk `callMembership` → `rtcMembership`. The SDK's vocabulary (architecture
document, "Vocabulary") settles the first three; the js-sdk rename is still open.
### Build targets before the migration
`vite-sdk.config.ts` (`pnpm build:sdk`), `vite-component.config.ts`,
`vite-embedded.config.ts`, `vite.config.ts`. The old SDK target
(`sdk-target-based-on-call-view-model/`) is the one whose dependency direction the
migration flips; it goes in slice 5.