Pages engine notes — v26.0

Chosen path
  Apple Pages (.pages)
    -> browser Web Worker
    -> ONLYOFFICE x2t WebAssembly v9.3.0+0
    -> real DOCX conversion (format id 65)
    -> PK/OOXML signature gate
    -> optional direct PDF attempt (format id 513)

If direct PDF is unavailable
  Do not construct a preview-image PDF and do not claim success.
  Keep DOCX available if it passed.
  Next phase is a browser-side ONLYOFFICE document renderer/export pipeline.

Why this is a new path
- It is not the v24/v25 File Viewer renderer.
- It is not cupertino-files layout reconstruction.
- It is not ZetaOffice/LibreOffice prebuilt WASM.
- It is not the v25 custom LOWA source-build path.
- x2t has its own Apple/iWork import path and has existing Emscripten builds.

Runtime packaging
- Runtime release is downloaded by tools/pages-x2t/install-runtime.mjs.
- x2t.zip SHA-512 release asset is required; failure to obtain/verify it aborts installation.
- x2t.js remains a normal static asset.
- x2t.wasm is split into 20 MiB chunks.
- src/index.js exposes the same logical byte stream at /wasm/x2t/x2t.wasm and supports Range requests.

Known risk
- WebAssembly memory failures and very large-file limitations have been reported in the upstream x2t WASM ecosystem. Therefore PC and mobile tests are separate acceptance gates.
- x2t direct PDF can require rendering components not present in a converter-only build. DOCX success and PDF success are deliberately separate.
