fix: pass actually fetched OIDs to process_newly_available_git_data

Previously, sync_identifier_from_url passed all needed OIDs to
process_newly_available_git_data, not just the OIDs that were
successfully fetched. This caused incorrect logging (new_oids_count
would show all needed OIDs, not just fetched ones).

While this didn't break functionality (the actual processing uses
can_apply_state which checks the repository on disk), it made
debugging confusing.

Changes:
- Rename oids_fetched to fetched_oids and change type from usize to Vec<String>
- Return Vec<String> from match arms instead of counts
- Pass fetched_oids (not needed_oids) to process_newly_available_git_data
- Return fetched_oids.len() at the end

This ensures logging accurately reflects which OIDs were actually
fetched from the remote.

src/purgatory/sync/functions.rs

@@ -368,7 +368,7 @@ pub async fn sync_identifier_from_url<C: SyncContext + ?Sized>(
     let fetch_result = ctx.fetch_oids(&target_repo, url, &needed_oids).await;
     throttle_manager.complete_request(&domain);
 
-    let oids_fetched = match fetch_result {
+    let fetched_oids = match fetch_result {
         Ok(fetched) if !fetched.is_empty() => {
             debug!(
                 identifier = %identifier,
@@ -376,7 +376,7 @@ pub async fn sync_identifier_from_url<C: SyncContext + ?Sized>(
                 oids_fetched = fetched.len(),
                 "Fetch succeeded"
             );
-            fetched.len()
+            fetched
         }
         Ok(_) => {
             debug!(
@@ -384,7 +384,7 @@ pub async fn sync_identifier_from_url<C: SyncContext + ?Sized>(
                 url = %url,
                 "Fetch returned no OIDs (not available on remote)"
             );
-            0
+            vec![]
         }
         Err(e) => {
             debug!(
@@ -393,13 +393,13 @@ pub async fn sync_identifier_from_url<C: SyncContext + ?Sized>(
                 error = %e,
                 "Fetch failed"
             );
-            0
+            vec![]
         }
     };
 
     // Try to process any events that can now be satisfied
-    if oids_fetched > 0 {
-        let new_oids: HashSet<String> = needed_oids.into_iter().collect();
+    if !fetched_oids.is_empty() {
+        let new_oids: HashSet<String> = fetched_oids.iter().cloned().collect();
         if let Err(e) = ctx
             .process_newly_available_git_data(&target_repo, &new_oids)
             .await
@@ -412,7 +412,7 @@ pub async fn sync_identifier_from_url<C: SyncContext + ?Sized>(
         }
     }
 
-    oids_fetched
+    fetched_oids.len()
 }
 
 /// Sync git data for an identifier.