fix: fondu du repli par masque CSS, indépendant du thème

Le dégradé vers --frss-background-color laissait une bande visible en thème
sombre (fond de l'article différent). Durcit aussi reset.php des tests e2e
(écriture atomique, attente de la revalidation opcache).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

static/read-more.css

@@ -5,18 +5,9 @@
 	box-sizing: border-box; /* configured height = visible height, padding included */
 	max-height: var(--read-more-height, 250px);
 	overflow: hidden;
-	position: relative;
-}
-
-.flux .text.read-more-collapsed::after {
-	content: "";
-	position: absolute;
-	left: 0;
-	right: 0;
-	bottom: 0;
-	height: 4em;
-	background: linear-gradient(to bottom, transparent, var(--frss-background-color, #fff));
-	pointer-events: none;
+	/* Fade out the last lines; a mask works with every theme background. */
+	-webkit-mask-image: linear-gradient(to bottom, #000 calc(100% - 4em), transparent);
+	mask-image: linear-gradient(to bottom, #000 calc(100% - 4em), transparent);
 }
 
 .flux .read-more-btn {

tests/e2e/read-more.spec.js

@@ -113,3 +113,15 @@ test('config height is clamped', async ({ page }) => {
 	expect(await text.evaluate((el) => getComputedStyle(el).maxHeight)).toBe('400px');
 	expect(await text.evaluate((el) => el.getBoundingClientRect().height)).toBeLessThanOrEqual(400);
 });
+
+test('fade is a theme-independent mask', async ({ page }) => {
+	await page.goto(READER);
+	const text = fluxByTitle(page, 1).locator('.text');
+	const mask = await text.evaluate((el) => {
+		const cs = getComputedStyle(el);
+		return cs.maskImage || cs.webkitMaskImage;
+	});
+	expect(mask).toContain('linear-gradient');
+	const overlay = await text.evaluate((el) => getComputedStyle(el, '::after').content);
+	expect(overlay === 'none' || overlay === 'normal').toBeTruthy();
+});

tests/e2e/reset.php

@@ -13,7 +13,14 @@ $conf['extensions_enabled']['Read More'] = true;
 $conf['extensions']['Read More']['collapsed_height'] = $height;
 $conf['mark_when']['scroll'] = true;
 $conf['view_mode'] = 'reader';
-file_put_contents($file, "<?php\nreturn " . var_export($conf, true) . ";\n");
+$new = "<?php\nreturn " . var_export($conf, true) . ";\n";
+// Only rewrite when changed, atomically: Apache's opcache revalidates every 2 s
+// and a half-written or freshly rewritten config can be served stale.
+if ($new !== file_get_contents($file)) {
+	file_put_contents("$file.tmp", $new);
+	rename("$file.tmp", $file);
+	sleep(3);
+}
 
 $pdo = new PDO("sqlite:$dir/db.sqlite");
 $pdo->exec('UPDATE entry SET is_read = 0');