Follow-ups after merging PR #3128 (with the #2990 preview work):
- PDF preview failed on every browser without
Map.prototype.getOrInsertComputed (Chrome < 145, Firefox < 144,
older Safari): "This file cannot be previewed" for any PDF. Load
pdf.js's legacy build, which bundles the polyfills for page and
worker, and bundle the worker through Vite (?worker&url) so
build.target lowers its class static block for Safari 16.0-16.3.
The browser-baseline check only scanned .js output and never saw
the copied .mjs worker; it scans .mjs too.
- PDF grid thumbnails only existed after someone opened the preview.
Page one is now rendered server-side with PDFium (pypdfium2, new
dependency, prebuilt wheels for every shipped platform) on upload,
ZIP extraction and external-folder scans; Generate Thumbnails
backfills PDFs as well. Renders are serialised behind a lock
(PDFium is not thread-safe), run off the event loop, and scale
from the page size so a huge MediaBox cannot allocate a huge
bitmap. Unreadable PDFs land without a thumbnail and keep the
browser fallback.
- A large STEP file takes over a minute to mesh in the browser and
showed only a spinner. STEP loads now show "Converting STEP
model... N s" and a note that large files can take a minute or
more, in all 15 locales.
- Drop the two occt-import-js "externalized for browser
compatibility" build warnings (path/crypto are only required in
its Node branch); any other externalization still shows.
