OPML: include each feed's refresh interval (TTL) in export/import (#8982)

Feeds moved between instances via OPML lost their refresh interval,
forcing manual reconfiguration. Add a 'frss:ttl' attribute (signed, so a
negative value also carries the muted state) to the OPML export, and read
it back on import. Documented in docs/en/developers/OPML.md.

For https://github.com/FreshRSS/FreshRSS/issues/5914

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

app/Services/ImportService.php

@@ -195,6 +195,11 @@ class FreshRSS_Import_Service {
 				$feed->_attribute('unicityCriteriaForced', true);
 			}
 
+			if (isset($feed_elt['frss:ttl'])) {
+				// Signed refresh interval (TTL); a negative value indicates a muted feed
+				$feed->_ttl((int)$feed_elt['frss:ttl']);
+			}
+
 			if (isset($feed_elt['frss:cssFullContent'])) {
 				$feed->_pathEntries(Minz_Helper::htmlspecialchars_utf8($feed_elt['frss:cssFullContent']));
 			}

app/views/helpers/export/opml.phtml

@@ -55,6 +55,11 @@ function feedsToOutlines(array $feeds, bool $excludeMutedFeeds = false): array {
 			$outline['frss:unicityCriteriaForced'] = 'true';
 		}
 
+		// Refresh interval (TTL), signed: a negative value indicates a muted feed
+		if ($feed->ttl(raw: true) !== FreshRSS_Feed::TTL_DEFAULT) {
+			$outline['frss:ttl'] = (string)$feed->ttl(raw: true);
+		}
+
 		if ($feed->kind() === FreshRSS_Feed::KIND_HTML_XPATH || $feed->kind() === FreshRSS_Feed::KIND_XML_XPATH) {
 			/** @var array<string,string> */
 			$xPathSettings = $feed->attributeArray('xpath') ?? [];

docs/en/developers/OPML.md

@@ -92,6 +92,7 @@ A number of [cURL options](https://curl.se/libcurl/c/curl_easy_setopt.html) are
 * `frss:priority`: Used for priority / visibility of the articles of that feed. Can be: `important`, `main` (default), `category`, `feed`, `hidden`.
 * `frss:unicityCriteria`: Criteria used for the unicity of articles. E.g. `id` (default), `link`, `sha1:link_published`, `sha1:link_published_title`, `sha1:title`, [etc](https://github.com/FreshRSS/FreshRSS/blob/1c92d55917029d291d00009b674d8552934a69ec/app/Models/Feed.php#L652-L666).
 * `frss:unicityCriteriaForced`: Boolean to force the usage of the selected unicity criterion even in the case of many duplicates (otherwise, the default behaviour is to fall back to a more precise unicity criteria).
+* `frss:ttl`: Refresh interval of the feed, in seconds. A negative value indicates a muted feed (automatic refresh disabled). When absent, the importing instance’s default refresh interval is used.
 * `frss:cssFullContent`: [CSS Selector](https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Selectors) to enable the download and extraction of the matching HTML section of each articles’ Web address.
 	* Example: `div.main, .summary`
 * `frss:cssContentFilter`: [CSS Selector](https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Selectors) to remove the matching HTML elements from the article content or from the full content retrieved by `frss:cssFullContent`.