fix: derive launch port from URL authority, not naive rsplit

reachable_lan_address() parsed the launch port with url.rsplit(':')
which yields "8096/" for manifest interfaces.main URLs that carry a
path (http://localhost:8096/). That fails to parse and silently drops
a perfectly reachable launch URL, so apps like jellyfin, btcpay-server,
fedimint, gitea, nextcloud and portainer showed running with no launch
link in the UI. New launch_url_port() reads digits after the final
colon (mirroring port_from_url in the RPC layer) and tolerates a
trailing path. Adds regression tests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

core/archipelago/src/container/docker_packages.rs

@@ -699,7 +699,7 @@ async fn reachable_lan_address(app_id: &str, candidate: Option<String>) -> Optio
     if !requires_reachable_launch(app_id) {
         return Some(url);
     }
-    let Some(port) = url.rsplit(':').next().and_then(|p| p.parse::<u16>().ok()) else {
+    let Some(port) = launch_url_port(&url) else {
         return None;
     };
     if launch_port_reachable(port).await {
@@ -710,6 +710,23 @@ async fn reachable_lan_address(app_id: &str, candidate: Option<String>) -> Optio
     }
 }
 
+/// Extract the TCP port from a launch URL's authority.
+///
+/// The candidate URL can carry a path when it comes from a manifest
+/// `interfaces.main` declaration (e.g. `http://localhost:8096/`). A naive
+/// `rsplit(':')` then yields `"8096/"`, which fails to parse and silently
+/// drops a reachable launch URL. Reading digits after the final colon mirrors
+/// `port_from_url` in the RPC layer and tolerates a trailing path.
+fn launch_url_port(url: &str) -> Option<u16> {
+    let after_colon = url.rsplit_once(':')?.1;
+    after_colon
+        .chars()
+        .take_while(|c| c.is_ascii_digit())
+        .collect::<String>()
+        .parse::<u16>()
+        .ok()
+}
+
 async fn launch_port_reachable(port: u16) -> bool {
     matches!(
         tokio::time::timeout(
@@ -788,3 +805,26 @@ fn package_state_str(state: &PackageState) -> &str {
         PackageState::Updating => "updating",
     }
 }
+
+#[cfg(test)]
+mod launch_url_port_tests {
+    use super::launch_url_port;
+
+    #[test]
+    fn parses_port_with_trailing_path() {
+        // Regression: manifest interfaces.main yields a path-suffixed URL.
+        // The old rsplit(':') parse produced "8096/" and dropped the URL.
+        assert_eq!(launch_url_port("http://localhost:8096/"), Some(8096));
+        assert_eq!(launch_url_port("http://localhost:8175/admin"), Some(8175));
+    }
+
+    #[test]
+    fn parses_bare_authority_port() {
+        assert_eq!(launch_url_port("http://localhost:8083"), Some(8083));
+    }
+
+    #[test]
+    fn rejects_url_without_port() {
+        assert_eq!(launch_url_port("http://localhost/"), None);
+    }
+}