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Component composition and fast previews

AutoPDF now models a document as an immutable component tree. A component is promoted through an exact (kind, variant, target) catalog definition, rendered to a content-addressed fragment, and assembled into a deterministic render manifest. The manifest records child/dependency edges, source assets, hashes, and editor source locations.

The LaTeX target maps layout coupling—not user-authored commands—to files:

  • flow becomes a \input fragment.
  • top-level section becomes an \include unit and may participate in \includeonly focused builds.
  • artifact embeds a separately resolved PDF or image.

\input by itself does not make TeX incrementally compile only that file. Fast feedback comes from the whole pipeline: component hash caching avoids rerendering unchanged fragments, bounded workers render independent components concurrently, only changed workspace files are written, the preview session retains TeX aux files, \includeonly skips unrelated section units, superseded builds are cancelled, and only changed page payloads are returned to the UI.

Production PDF generation remains behind the existing stable api.Result boundary. Preview is deliberately a separate, revisioned lifecycle so stale output can never replace a newer browser revision.

Public flow

  1. Create immutable component definitions and freeze a component.Catalog, or use api.NewDefaultDocumentEngine("latex", config).
  2. Call DocumentEngine.Project for a pure manifest/projection, or DocumentEngine.Generate with a production ProjectionGenerator.
  3. For interactive use, retain one preview.Session per editor document and submit edits through DocumentEngine.Preview.
  4. Give mutable external assets a new URI or AssetRef.Digest whenever their bytes change; this intentionally invalidates the relevant fragment/source.

The compiler and asset resolver are explicit effect ports. This keeps component renderers deterministic and makes caches safe to share across requests.

Concrete adapters

  • api.NewProjectionGenerator materializes a projection in an isolated production workspace, resolves versioned assets, and calls the canonical Engine.Generate pipeline while preserving api.Result.
  • preview.NewLaTeXCompiler retains TeX auxiliary state in each session, terminates superseded compiler processes through context cancellation, and performs full-resolution rasterization only for changed page fingerprints.
  • rest.NewPreviewAPI exposes monotonic revisions and replayable SSE events. A browser reducer replaces changedPages, deletes removedPages, and ignores older revisions.

Layered budgets and the browser paint hook are documented in Preview performance.