fix: more aggressive user agent for URL preview

adding "facebookexternalhit" alongside "embedbot" fixes many errors, such as YouTube Music's:
    "Your browser is deprecated. Please upgrade."

add admin command to clear URL stuck and broken data (per URL currently)

    add command to clear all saved URL previews.
    sync resolver docs.

src/admin/media/commands.rs

@@ -388,3 +388,19 @@ pub(super) async fn get_remote_thumbnail(
 	self.write_str(&format!("```\n{result:#?}\nreceived {len} bytes for file content.\n```"))
 		.await
 }
+
+#[admin_command]
+pub(super) async fn delete_url_preview(&self, url: Option<String>, all: bool) -> Result {
+	if all {
+		self.services.media.clear_url_previews().await;
+
+		return self.write_str("Deleted all cached URL previews.").await;
+	}
+
+	let url = url.expect("clap enforces url is required unless --all");
+
+	self.services.media.remove_url_preview(&url).await?;
+
+	self.write_str(&format!("Deleted cached URL preview for: {url}"))
+		.await
+}

src/admin/media/mod.rs

@@ -108,4 +108,16 @@ pub enum MediaCommand {
 		#[arg(long, default_value("800"))]
 		height: u32,
 	},
+
+	/// Deletes a cached URL preview, forcing it to be re-fetched.
+	/// Use --all to purge all cached URL previews.
+	DeleteUrlPreview {
+		/// The URL to clear from the saved preview data
+		#[arg(required_unless_present = "all")]
+		url: Option<String>,
+
+		/// Purge all cached URL previews
+		#[arg(long, conflicts_with = "url")]
+		all: bool,
+	},
 }

src/admin/query/resolver.rs

@@ -20,7 +20,17 @@ pub enum ResolverCommand {
 		name: Option<String>,
 	},
 
-	/// Flush a specific server from the resolver caches or everything
+	/// Flush a given server from the resolver caches or flush them completely
+	///
+	/// * Examples:
+	///   * Flush a specific server:
+	///
+	///     `!admin query resolver flush-cache matrix.example.com`
+	///
+	///   * Flush all resolver caches completely:
+	///
+	///     `!admin query resolver flush-cache --all`
+	#[command(verbatim_doc_comment)]
 	FlushCache {
 		name: Option<OwnedServerName>,
 

src/core/info/version.rs

@@ -14,6 +14,7 @@ static SEMANTIC: &str = env!("CARGO_PKG_VERSION");
 static VERSION: OnceLock<String> = OnceLock::new();
 static VERSION_UA: OnceLock<String> = OnceLock::new();
 static USER_AGENT: OnceLock<String> = OnceLock::new();
+static USER_AGENT_MEDIA: OnceLock<String> = OnceLock::new();
 
 #[inline]
 #[must_use]
@@ -21,14 +22,22 @@ pub fn name() -> &'static str { BRANDING }
 
 #[inline]
 pub fn version() -> &'static str { VERSION.get_or_init(init_version) }
+
 #[inline]
 pub fn version_ua() -> &'static str { VERSION_UA.get_or_init(init_version_ua) }
 
 #[inline]
 pub fn user_agent() -> &'static str { USER_AGENT.get_or_init(init_user_agent) }
 
+#[inline]
+pub fn user_agent_media() -> &'static str { USER_AGENT_MEDIA.get_or_init(init_user_agent_media) }
+
 fn init_user_agent() -> String { format!("{}/{} (bot; +{WEBSITE})", name(), version_ua()) }
 
+fn init_user_agent_media() -> String {
+	format!("{}/{} (embedbot; facebookexternalhit/1.1; +{WEBSITE})", name(), version_ua())
+}
+
 fn init_version_ua() -> String {
 	conduwuit_build_metadata::version_tag()
 		.map_or_else(|| SEMANTIC.to_owned(), |extra| format!("{SEMANTIC}+{extra}"))

src/service/client/mod.rs

@@ -39,7 +39,7 @@ impl crate::Service for Service {
 		let url_preview_user_agent = config
 			.url_preview_user_agent
 			.clone()
-			.unwrap_or_else(|| conduwuit::version::user_agent().to_owned());
+			.unwrap_or_else(|| conduwuit::version::user_agent_media().to_owned());
 
 		Ok(Arc::new(Self {
 			default: base(config)?

src/service/media/data.rs

@@ -170,6 +170,8 @@ impl Data {
 		Ok(())
 	}
 
+	pub(super) async fn clear_url_previews(&self) { self.url_previews.clear().await; }
+
 	pub(super) fn set_url_preview(
 		&self,
 		url: &str,

src/service/media/preview.rs

@@ -37,6 +37,9 @@ pub async fn remove_url_preview(&self, url: &str) -> Result<()> {
 	self.db.remove_url_preview(url)
 }
 
+#[implement(Service)]
+pub async fn clear_url_previews(&self) { self.db.clear_url_previews().await; }
+
 #[implement(Service)]
 pub async fn set_url_preview(&self, url: &str, data: &UrlPreviewData) -> Result<()> {
 	let now = SystemTime::now()