@live-change/codemirror-service

LiveChange service definition for collaborative CodeMirror 6 documents: stores document text as line arrays, applies incoming ChangeSet updates, keeps an append-only steps history, and optional snapshots for faster replay.

What is implemented

• Models (model.js): Document, StepsBucket, Snapshot; in-memory LRU cache of open documents for hot apply path.
• Events: documentCreated, documentEdited, snapshotTaken — persist content, version, buckets, snapshots.
• Views (index.js): document (by targetType + target), steps (range), snapshot (single version), snapshots (range index).
• Actions: createDocument, createDocumentIfNotExists, edit, takeSnapshot; trigger takeSnapshot.
• Collaboration merge: rebaseUpdates from @codemirror/collab runs in the edit action (before emit), not in the event. When the client version lags the open document, intermediate steps are loaded from StepsBucket, rebased, and only then emitted. If rebase throws, the action returns rejected and does not emit documentEdited.
• Event documentEdited: deterministic persistence only — deserialize steps, apply sequentially to authoritative text, bump version, write Document and StepsBucket. It expects version to match the open document; a mismatch is a controlled logicError (should not happen after a successful edit emit).

Configuration

In the host app services.config.js, register this package with documentTypes: an object whose keys are allowed document type strings. Values are currently opaque (used only for presence); optional metadata like format: 'text' is fine.

Example (see frontend/codemirror-frontend/server/services.config.js):

{
  name: 'codemirror',
  path: '@live-change/codemirror-service',
  documentTypes: {
    markdown: { format: 'text' },
    code: { format: 'text' }
  }
}

Related package

• UI and transport: @live-change/codemirror-frontend.