diff --git a/crates/buzz-relay/src/client_info.rs b/crates/buzz-relay/src/client_info.rs
index 445a2fb1b..54e3f4c02 100644
--- a/crates/buzz-relay/src/client_info.rs
+++ b/crates/buzz-relay/src/client_info.rs
@@ -35,8 +35,18 @@ impl ClientInfo {
     /// counter and also returns `None`, so it can never reject a request.
     #[must_use]
     pub fn from_headers(headers: &HeaderMap) -> Option<Self> {
-        let value = headers.get("buzz-client")?;
-        let parsed = value.to_str().ok().and_then(|raw| Self::parse(raw).ok());
+        let all_values = headers.get_all("buzz-client");
+        let mut values = all_values.iter();
+        let first = values.next()?;
+        let parsed = (|| {
+            let mut raw = first.to_str().map_err(|_| ())?.to_owned();
+            for value in values {
+                raw.push_str(", ");
+                raw.push_str(value.to_str().map_err(|_| ())?);
+            }
+            Self::parse(&raw)
+        })()
+        .ok();
         if parsed.is_none() {
             metrics::counter!("buzz_client_header_parse_failures_total").increment(1);
         }
@@ -265,6 +275,43 @@ mod tests {
         assert_eq!(parse_failures(&recorder), 0);
     }
 
+    #[test]
+    fn joins_multiple_header_lines_before_parsing() {
+        let mut headers = HeaderMap::new();
+        headers.append(
+            "buzz-client",
+            HeaderValue::from_static(r#"v=1, app=buzz-mobile, platform=ios, app-version="0.4.5""#),
+        );
+        headers.append(
+            "buzz-client",
+            HeaderValue::from_static(r#"app-build="6", os-version="18.5""#),
+        );
+
+        let client = ClientInfo::from_headers(&headers).expect("valid combined header");
+        assert_eq!(client.app_version, "0.4.5");
+        assert_eq!(client.app_build, "6");
+        assert_eq!(client.os_version, "18.5");
+    }
+
+    #[test]
+    fn rejects_non_utf8_in_any_header_line() {
+        let recorder = DebuggingRecorder::new();
+        let mut headers = HeaderMap::new();
+        headers.append(
+            "buzz-client",
+            HeaderValue::from_static(r#"v=1, app=buzz-mobile, platform=ios, app-version="0.4.5""#),
+        );
+        headers.append(
+            "buzz-client",
+            HeaderValue::from_bytes(&[0xff]).expect("opaque test header value"),
+        );
+
+        metrics::with_local_recorder(&recorder, || {
+            assert_eq!(ClientInfo::from_headers(&headers), None);
+        });
+        assert_eq!(parse_failures(&recorder), 1);
+    }
+
     #[test]
     fn malformed_or_semantically_invalid_header_is_absent_and_counted() {
         for raw in [
diff --git a/mobile/lib/features/invites/invite_join_provider.dart b/mobile/lib/features/invites/invite_join_provider.dart
index 040371f95..d844a4b11 100644
--- a/mobile/lib/features/invites/invite_join_provider.dart
+++ b/mobile/lib/features/invites/invite_join_provider.dart
@@ -131,6 +131,8 @@ class InviteJoinNotifier extends Notifier<InviteJoinState> {
               ...clientHeadersForUrl(
                 headers: ref.read(clientHeadersProvider),
                 targetUrl: url,
+                // Explicit confirmation makes the invite relay the user's
+                // intended first-party destination for this claim.
                 relayUrl: invite.relayUrl,
               ),
               'Authorization': buildNip98AuthHeader(
diff --git a/mobile/lib/shared/relay/media_auth.dart b/mobile/lib/shared/relay/media_auth.dart
index 4a2111f8c..9ed78d6a3 100644
--- a/mobile/lib/shared/relay/media_auth.dart
+++ b/mobile/lib/shared/relay/media_auth.dart
@@ -57,7 +57,8 @@ class MediaGetAuthService {
           );
     final uri = Uri.tryParse(url);
     final relayUri = Uri.tryParse(_baseUrl);
-    if (uri == null || relayUri == null) return const {};
+    if (uri == null) return const {};
+    if (relayUri == null) return identificationHeaders;
     if (!_isRelayMediaUrl(uri, relayUri)) return identificationHeaders;
 
     final nsec = _nsec;
diff --git a/mobile/test/shared/relay/media_image_test.dart b/mobile/test/shared/relay/media_image_test.dart
index 61b5a2ff4..cd3557011 100644
--- a/mobile/test/shared/relay/media_image_test.dart
+++ b/mobile/test/shared/relay/media_image_test.dart
@@ -102,6 +102,38 @@ void main() {
       expect(headers, isNot(contains('Authorization')));
     });
 
+    test('sends only User-Agent when the relay base URL is malformed', () {
+      const clientHeaders = ClientHeaders(
+        appVersion: '1.0',
+        buzzClient: 'test-client',
+        userAgent: 'test-agent',
+      );
+      final auth = MediaGetAuthService(
+        baseUrl: '://',
+        nsec: nostr.Keys.generate().nsec,
+        clientHeaders: clientHeaders,
+      );
+
+      expect(
+        auth.headersFor('https://cdn.cloudflare.example/attachments/abc.png'),
+        {'User-Agent': 'test-agent'},
+      );
+    });
+
+    test('malformed target URL gets no headers', () {
+      const clientHeaders = ClientHeaders(
+        appVersion: '1.0',
+        buzzClient: 'test-client',
+        userAgent: 'test-agent',
+      );
+      final auth = _auth(
+        nsec: nostr.Keys.generate().nsec,
+        clientHeaders: clientHeaders,
+      );
+
+      expect(auth.headersFor('://'), isEmpty);
+    });
+
     test('sends identification without a signing key', () {
       const clientHeaders = ClientHeaders(
         appVersion: '1.0',