feat: show preview thumbnails in the list view

[karlitschek]

Fill the NcListItem icon slot with a small (40px, 80px requested for hidpi) lazy-loaded preview thumbnail, using the same etag cache-busting as the grid view. getPreviewUrl() gained a size parameter so the grid keeps its 300px previews. Falls back to a document icon when the preview request fails; mimeFallback=true keeps that case rare.

Includes rebuilt assets.

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI

[karlitschek]

@emberfiend

[moodyjmz]

Stacked on #79's branch, so it inherits that PR's problems. Base branch is fix/recent-files-sort-order (#79), not main — once #79 is closed and redone against current main, this needs a full rebase too (the OfficeOverview.vue here still has the pre-refactor layout; main's test harness for this file doesn't exist on this branch at all). DCO is also failing (no Signed-off-by:).

Details

The feature diff itself is small and clean — no blockers in the code:

• Security: clean. getPreviewUrl()'s params are either hardcoded literals (size: 80/300) or server-supplied (fileid, etag); generateUrl encodes substitutions. Nothing user-controlled reaches the URL.
• a11y: the list thumbnail's alt="" is the correct call, not a regression — NcListItem's :name prop already renders the filename as accessible text, so an empty alt avoids double-announcing it to a screen reader.
• Performance: real but minor tradeoff — list view goes from zero preview requests to matching grid view's cost. loading="lazy" genuinely mitigates it (200 rows is far taller than any viewport), so this isn't a "200 requests on load" problem. Worth knowing this is a deliberate tradeoff, not a regression to fix.
• The shared failedPreviews cache (keyed only by fileid, now used by both the 300px grid and 80px list requests) can in theory let a failure at one size suppress the thumbnail at the other after a view switch. In practice this is close to moot — Nextcloud's /core/preview with mimeFallback=true clamps oversized requests and returns a 200 with a mimetype icon rather than erroring, so @error only fires on failures that are size-independent anyway (missing provider, permissions). Worth a one-line comment in the code; not worth blocking on.

Test coverage — the real gap. No existing test (grid or list, old or new) covers getPreviewUrl(), the failedPreviews fallback-to-icon behaviour, or preview rendering at all — and this branch doesn't even have the OfficeOverview.spec.ts harness that exists on main. Once rebased, worth adding:

1. List view renders the thumbnail <img> with size=80 reflected in the URL (x=80&y=80).
2. getPreviewUrl()'s URL shape, including the 6-char etag v param, for a given size.
3. @error flips failedPreviews[fileid] and swaps to the document-icon fallback — for both grid and list.

Suggested path: hold until #79 is resolved, then rebase this onto the redone base, pull in OfficeOverview.spec.ts, add the three tests above, and sign off the commit.

[moodyjmz]

Superseded by #87 — rebased onto current main (this PR's base predated the file-filtering refactor), with Frank's original diagnosis and feature credited via Co-authored-by:, the shared-failedPreviews-across-sizes issue fixed via a dedicated FilePreview component, and tests added. Will close this once #87 merges.

[moodyjmz]

Superseded by #87, now merged as bf7e76b.

Attribution carried over: the feature commit on main is 20eb90e, with Co-authored-by: Frank Karlitschek.

#87 is the version that landed — rebased onto current main, DCO signed off, and with unit tests (src/components/FilePreview.spec.ts, plus additions to src/views/OfficeOverview.spec.ts).

Closing this one.