[Epic] @maic SDK family: from in-app implementations to package consumers

[wyuc]

Goal

Evolve the app (and downstream consumers) from "ships its own slide stack" to a
standard consumer of the @maic/{dsl, renderer, importer, exporter} package
family. End state: the app keeps only business glue (media-store resolution,
lazy placeholders, app chrome); every contract, renderer, importer and exporter
lives in a package with a published boundary.

Dependency rule (established in #668, kept acyclic):
@maic/dsl → nothing; renderer / importer / exporter → @maic/dsl only.

Where we are (done)

• feat(packages): introduce maic-import and maic-renderer workspace packages #668 extracted @maic/dsl (pure contract), @maic/renderer (read-only
  canvas, v1), @maic/importer (pptx → DSL); app consumes the importer.
• refactor(app): consume @maic/dsl + @maic/renderer in the app (slide types + read-only thumbnails) #707 made the app consume dsl + renderer: lib/types/slides.ts is a
  thin re-export shim of @maic/dsl; the three read-only thumbnail
  surfaces render through SlideCanvas (with reactive gen_* media
  resolution in the app-side wrapper).

Phase 1 — Cleanup & consolidation (low risk, immediately actionable)

• Delete dead legacy ThumbnailSlide/ + ThumbnailElement (zero imports
  after refactor(app): consume @maic/dsl + @maic/renderer in the app (slide types + read-only thumbnails) #707, ~217 LOC)
• Repoint ~90 @/lib/types/slides import sites directly at @maic/dsl,
  then delete the shim
• Fix @maic/dsl build: extensionless re-exports in dist/index.js break
  bare-node ESM resolution (emit .js extensions)
• Publish @maic/dsl, @maic/renderer, @maic/importer to npm
  (publishConfig is already in place) — unlocks all out-of-workspace
  consumers

Phase 2 — Grow the DSL (needs contract design)

• Promote the pure Stage / Scene / SceneContent types from
  lib/types/stage.ts into @maic/dsl (blocker: they currently couple to
  Action / Widget / generation types — split the pure parts first; already
  on the dsl README roadmap)
• Bring the Action DSL (lib/types/action.ts) into the contract
  (@maic/dsl or a sibling package)
• Add the JSON Schema + pure validators for the slide contract (serves
  non-TS consumers)
• Activate DSL_VERSION + the migration registry

Phase 3 — renderer v2: the editing surface (largest item, critical path)

• @maic/renderer v2: selection, drag/resize/rotate, operate handles,
  ProseMirror inline editing (v1 is read-only by design)
• Absorb the app's components/slide-renderer/Editor/ (~38 files) and the
  full-size components/element/ renderers (~41 files) — the last big
  duplicated implementation in the app
• After absorption, components/slide-renderer/ keeps only business glue
  (SlideThumbnail-style wrappers, ThumbnailInteractive)

Phase 4 — exporter & closing the family (parallel to Phase 3)

• Create @maic/exporter (the reserved 4th member): extract PPTX / HTML /
  offline-ZIP export from lib/export
• Switch the app's export paths to consume it; retire the
  sync-maic-importer.mjs vendor step in favor of normal package deps

Phase 5 — ecosystem consumers (unlocked by Phase 1 publish)

• External editors/apps adopt @maic/dsl instead of vendored slide-type
  copies, @maic/importer for pptx import, and (where read-only suffices)
  @maic/renderer for display — peer requirements: React ≥18, Tailwind 4

Principles

• Business glue (media-generation store resolution, lazy placeholders, app
  badges) stays in the consumer, never in the packages.
• Migrate incrementally: shim/wrapper first, batch-switch imports, delete the
  legacy code last (the slides shim is the precedent).
• @maic/dsl never gains a runtime dependency; cross-package enums stay
  regular enums.

Risks

• renderer v2's editing surface is the bulk of the remaining work and gates
  Phase 3; worth starting design early.
• The Stage/Action type split needs contract review before Phase 2 lands.

[wyuc]

Phase 1 progress

• Remove dead ThumbnailSlide / ThumbnailElement — chore(phase-1): drop dead ThumbnailSlide + fix @maic/dsl Node ESM resolution #736
• Fix @maic/dsl Node ESM resolution (.js extensions + NodeNext) — chore(phase-1): drop dead ThumbnailSlide + fix @maic/dsl Node ESM resolution #736
• Repoint ~100 @/lib/types/slides import sites directly at @maic/dsl and delete the shim — refactor(types): consume @maic/dsl directly and drop the slides re-export shim #738
• Publish @maic/dsl / @maic/renderer / @maic/importer to npm — requires an npm publish token (maintainer action); the packages already carry publishConfig. Deferred to a maintainer with publish rights.

With the shim gone and imports pointing at the package, the in-app type indirection is fully removed. The npm-publish step is the only remaining Phase-1 item and is a maintainer/release action rather than a code change.

Next: Phase 2 (DSL growth)

Starting on promoting the pure Stage / Scene / SceneContent types into @maic/dsl. These currently couple to Action / widget / generation types in the app, so the first step is splitting the pure structural types from the app-coupled ones; will scope that in a dedicated PR.