fix(reader): fit wide vector PDF pages to the screen

[ajslater]

Summary

Follow-up to #951. None of the four canvas rules in pdf-doc.vue matched the rendered canvas, in any fit mode. They have been dead since the Vuetify 3 port (Dec 2022), when an unscoped <style> block became top-level :deep() selectors:

1. Scoping. :deep(.vue-pdf-embed.X > div > canvas) compiles to [data-v-x] .vue-pdf-embed.X > div > canvas, which needs a scoped ancestor. The embed is the component's root, so there isn't one. The rules now scope on the root (.pdfDoc.X :deep(canvas) → .pdfDoc.X[data-v-x] canvas).
2. Depth. vue-pdf-embed 2.1.6 renders > div > div.vue-pdf-embed__page > canvas, one level deeper than > div > canvas. A descendant canvas covers it.

Per-rule decisions

I made each rule match, then measured it live (Force vector, DPR 2, 1024×768 and 390×844, portrait pages plus a wide page):

Rule	Effect once live	Decision
fitToHeightTwo, fitToScreenTwo: width: inherit !important	None. vue-pdf-embed already sets an aspect-correct inline width/height, and auto derives the same width.	Deleted
fitToWidthTwo: height: inherit !important	None (a 1px rounding difference)	Deleted
fitToOrigTwo: width/height: inherit !important	Both become auto, so the canvas shows at its bitmap size: 1023×1581 instead of 512×790, 2x on HiDPI, with a 2046px scroll width. Zoom > 1 also produces fitToOrig*, so zoomed pages would blow up too.	Deleted
fitToScreen*: object-fit: contain	None. The box already matches the bitmap, so there is nothing to contain.	Kept and adjusted. Paired with max-width: 100vw (single/vertical) or 50vw (two-page), as page-img.vue does for images

Original Size already renders like Fit to Width (pdf-doc.vue's width computed), and that doesn't change here. The fitToOrigTwo rule would only have taken effect once #951 landed. The misleading "Wide PDFs will not fit to SCREEN well" comment is replaced.

Visible change

This affects only Fit to Screen, and only pages wider than the screen:

• Two-page, 1024×768, wide spread + portrait page: the scroll width goes from 1491px to 1024px. The spread is capped at 512px and letterboxed.
• Single page, 390×844, wide page: the canvas goes from 1092px (overflowing, the same as Fit to Height) to a 390×844 box with the page letterboxed.
• Vertical, 390×844: a page is capped at 390px inside its 80%-height box. This includes portrait pages, which were 437px wide there. Letterbox bands appear above and below wide pages, as in image mode.

Every other mode (Width, Height, Original × single/two/vertical) measured identical to before, down to the pixel. Zoom (fitToOrig* class) is not capped: at 2x the canvas stays at 2185×1688.

NEWS: "Fit to Screen fits wide pages when PDFs render as vectors."

Tests

• make fix: no changes beyond this diff. make lint: clean (two basedpyright warnings in cover.py were already there).
• bunx vitest run: 88 files, 919 tests passed.
• No unit test: this is canvas layout, which happy-dom can't measure. I verified it in a real browser against a dev stack with a generated 6-page PDF (four portrait pages, one wide spread, one portrait page).

🤖 Generated with Claude Code