fix(tables): drop the card image where no preview can be fetched

A preview is served against the viewer's session, so on a public link there is
none to authenticate with and the image can never arrive. Cards still asked for
one, leaving a broken image on every card of a shared tiles or gallery view.

Ask for no preview at all when there is no session, and take the image area out
of the card rather than leaving it empty, so a shared card reads as the text it
can actually show. The title then has the whole card to use instead of a share
of an image that is not there.

Assisted-by: ClaudeCode:claude-opus-5
Signed-off-by: Andy Scherzinger <info@andy-scherzinger.de>

Author: AndyScherzinger

src/shared/components/ncTable/sections/CustomTable.vue

@@ -56,7 +56,7 @@
 		<div v-else
 			ref="cardLayout"
 			class="card-layout"
-			:class="[`card-layout--${currentLayout}`, { 'card-layout--no-image': !hasCardBackground }]"
+			:class="[`card-layout--${currentLayout}`, { 'card-layout--no-image': !hasCardBackground, 'card-layout--no-previews': !canRenderPreviews }]"
 			:style="{ '--card-title-lines': cardTitleLines }">
 			<button v-for="row in currentPageRows"
 				:key="row.id"
@@ -105,6 +105,7 @@ import { NcRichText } from '@nextcloud/vue'
 import { ColumnTypes } from '../mixins/columnHandler.js'
 import { translate as t } from '@nextcloud/l10n'
 import { generateUrl } from '@nextcloud/router'
+import { getCurrentUser } from '@nextcloud/auth'
 
 // Share of the card image the title banner may cover before the text is ellipsized.
 const MAX_TITLE_BANNER_SHARE = 0.6
@@ -177,8 +178,15 @@ export default {
 	},
 
 	computed: {
+		// A preview is served against the viewer's session. Without one, as on a public link,
+		// it can never load, so the card is laid out as if it had no image at all rather than
+		// reserving space for something that will stay empty.
+		canRenderPreviews() {
+			return getCurrentUser() !== null
+		},
 		hasCardBackground() {
-			return this.localViewSetting?.viewSettings?.cardBackgroundSource !== null
+			return this.canRenderPreviews
+				&& this.localViewSetting?.viewSettings?.cardBackgroundSource !== null
 				&& this.localViewSetting?.viewSettings?.cardBackgroundSource !== undefined
 		},
 		currentLayout() {
@@ -256,6 +264,12 @@ export default {
 		},
 
 		updateCardTitleLines() {
+			// With no image area to share, the title is simply the text of the card and the
+			// geometry below would measure the title against itself.
+			if (!this.canRenderPreviews) {
+				this.cardTitleLines = MAX_TITLE_LINES
+				return
+			}
 			const container = this.$refs.cardLayout
 			const wrapper = container?.querySelector('.layout-card__image-wrapper')
 			const banner = container?.querySelector('.layout-card__title-banner')
@@ -334,6 +348,9 @@ export default {
 			return row?.data?.find(item => item?.columnId === columnId) ?? null
 		},
 		getPreviewUrl(row) {
+			if (!this.canRenderPreviews) {
+				return null
+			}
 			const backgroundColumn = this.getBackgroundColumn()
 			const rawValue = this.getCell(row, backgroundColumn?.id)?.value
 			if (rawValue === null || rawValue === undefined || rawValue === '') {
@@ -546,6 +563,22 @@ export default {
 	bottom: auto;
 }
 
+/* Without a session a preview can never arrive, so the image area is not just left empty but
+   taken out of the card: the title flows straight into the card instead. */
+.card-layout--no-previews .layout-card__image-wrapper {
+	aspect-ratio: auto;
+	background: none;
+}
+
+.card-layout--no-previews .layout-card__no-image {
+	display: none;
+}
+
+.card-layout--no-previews .layout-card__title-banner {
+	position: static;
+	max-height: none;
+}
+
 .layout-card__title-text {
 	display: -webkit-box;
 	-webkit-line-clamp: var(--card-title-lines, 2);