Add sync_identifier orchestration and ThrottleManager queue processing

Implement the main sync orchestration function and trigger-based queue
processing for throttled domains:

sync_identifier function:
- Orchestrates syncing git data for a single identifier
- Tries all non-throttled URLs in sequence
- Checks completion after each fetch (no pending events or all OIDs fetched)
- Enqueues with throttled domains when non-throttled URLs are exhausted
- Returns true if complete, false if events remain (for backoff)

ThrottleManager enhancements:
- Add set_context() to provide SyncContext for queue processing
- Add try_process_next() to spawn tasks when capacity frees
- Add process_queued_identifier() to handle queued work
- Update complete_request() to trigger processing on completion
- Update enqueue_identifier() to trigger processing when capacity available
- Add internal methods for non-Arc testing compatibility

Generic function updates:
- Add ?Sized bound to sync_identifier_next_url, sync_identifier_from_url,
  sync_identifier, and get_throttled_domains_with_untried_urls for
  dynamic dispatch support (Arc<dyn SyncContext>)

Tests:
- sync_identifier_tries_multiple_urls_until_complete: verifies sequential
  URL fetching until all OIDs are available
- sync_identifier_enqueues_throttled_domains_when_incomplete: verifies
  throttled domains get the identifier enqueued for later processing
- has_queued_work_reflects_queue_state: verifies queue state tracking

1 files changed, 225 insertions, 3 deletions

diff --git a/src/purgatory/sync/functions.rs b/src/purgatory/sync/functions.rs
index de846f3..751dd5e 100644
--- a/src/purgatory/sync/functions.rs
+++ b/src/purgatory/sync/functions.rs
@@ -55,7 +55,7 @@ fn extract_domain(url: &str) -> Option<String> {
 ///
 /// * `Some(url)` - The next URL to try
 /// * `None` - No suitable URL found (all tried, all throttled, or no URLs available)
-pub async fn sync_identifier_next_url<C: SyncContext>(
+pub async fn sync_identifier_next_url<C: SyncContext + ?Sized>(
     ctx: &C,
     identifier: &str,
     domain: Option<&str>,
@@ -178,7 +178,7 @@ pub struct ThrottledDomainInfo {
 ///
 /// A list of throttled domains that still have untried URLs, along with
 /// the tried URLs for each domain (for proper queue state).
-pub async fn get_throttled_domains_with_untried_urls<C: SyncContext>(
+pub async fn get_throttled_domains_with_untried_urls<C: SyncContext + ?Sized>(
     ctx: &C,
     identifier: &str,
     tried_urls: &HashSet<String>,
@@ -254,7 +254,7 @@ pub async fn get_throttled_domains_with_untried_urls<C: SyncContext>(
 /// # Returns
 ///
 /// The number of OIDs successfully fetched (0 on failure)
-pub async fn sync_identifier_from_url<C: SyncContext>(
+pub async fn sync_identifier_from_url<C: SyncContext + ?Sized>(
     ctx: &C,
     identifier: &str,
     url: &str,
@@ -347,6 +347,128 @@ pub async fn sync_identifier_from_url<C: SyncContext>(
     oids_fetched
 }
 
+/// Sync git data for an identifier.
+///
+/// This is the main orchestration function called by the sync loop. It:
+/// 1. Tries all non-throttled URLs in sequence
+/// 2. After each fetch, checks if sync is complete (no pending events or no needed OIDs)
+/// 3. When no non-throttled URLs remain, enqueues with throttled domains for later processing
+/// 4. Returns without waiting for throttled domains to complete
+///
+/// # Arguments
+///
+/// * `ctx` - The sync context providing repository data and OID information
+/// * `identifier` - The repository identifier (d-tag value)
+/// * `throttle_manager` - Used for rate limiting and domain queue management
+///
+/// # Returns
+///
+/// * `true` - Sync completed (no pending events or all OIDs fetched)
+/// * `false` - Events remain in purgatory (will be retried after backoff, or processed
+///   by throttled domain queues)
+pub async fn sync_identifier<C: SyncContext + ?Sized>(
+    ctx: &C,
+    identifier: &str,
+    throttle_manager: &Arc<ThrottleManager>,
+) -> bool {
+    let mut tried_urls: HashSet<String> = HashSet::new();
+
+    debug!(
+        identifier = %identifier,
+        "Starting sync for identifier"
+    );
+
+    // Try all non-throttled URLs
+    loop {
+        match sync_identifier_next_url(ctx, identifier, None, &tried_urls, throttle_manager).await {
+            Some(url) => {
+                debug!(
+                    identifier = %identifier,
+                    url = %url,
+                    "Found non-throttled URL to try"
+                );
+
+                // Fetch from this URL
+                sync_identifier_from_url(ctx, identifier, &url, throttle_manager).await;
+                tried_urls.insert(url);
+
+                // Check if sync is now complete
+                if !ctx.has_pending_events(identifier) {
+                    debug!(
+                        identifier = %identifier,
+                        "Sync complete - no pending events"
+                    );
+                    return true;
+                }
+
+                let needed_oids = ctx.collect_needed_oids(identifier);
+                if needed_oids.is_empty() {
+                    debug!(
+                        identifier = %identifier,
+                        "Sync complete - all OIDs available"
+                    );
+                    return true;
+                }
+
+                // Continue trying more URLs
+            }
+            None => {
+                // No more non-throttled URLs available
+                debug!(
+                    identifier = %identifier,
+                    tried_count = tried_urls.len(),
+                    "No more non-throttled URLs available"
+                );
+                break;
+            }
+        }
+    }
+
+    // Check if we're done (no pending events or no needed OIDs)
+    if !ctx.has_pending_events(identifier) {
+        debug!(
+            identifier = %identifier,
+            "Sync complete after exhausting URLs - no pending events"
+        );
+        return true;
+    }
+
+    let needed_oids = ctx.collect_needed_oids(identifier);
+    if needed_oids.is_empty() {
+        debug!(
+            identifier = %identifier,
+            "Sync complete after exhausting URLs - all OIDs available"
+        );
+        return true;
+    }
+
+    // Enqueue with any throttled domains that have untried URLs
+    let throttled_domains =
+        get_throttled_domains_with_untried_urls(ctx, identifier, &tried_urls, throttle_manager)
+            .await;
+
+    for info in throttled_domains {
+        debug!(
+            identifier = %identifier,
+            domain = %info.domain,
+            "Enqueueing identifier with throttled domain"
+        );
+        throttle_manager.enqueue_identifier(
+            &info.domain,
+            identifier.to_string(),
+            info.tried_urls_for_domain,
+        );
+    }
+
+    // Return false - events remain, will retry after backoff
+    // (throttled domains will process independently)
+    debug!(
+        identifier = %identifier,
+        "Sync incomplete - returning false for backoff"
+    );
+    false
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -617,4 +739,104 @@ mod tests {
         assert_eq!(throttled[0].domain, "gitlab.com");
         assert!(throttled[0].tried_urls_for_domain.is_empty());
     }
+
+    // =========================================================================
+    // Phase 6: sync_identifier tests
+    // =========================================================================
+
+    #[tokio::test]
+    async fn sync_identifier_tries_multiple_urls_until_complete() {
+        // Set up mock with 3 URLs, each providing partial OIDs
+        // URL1 provides abc123, URL2 provides def456, URL3 provides ghi789
+        let mock = MockSyncContext::new()
+            .with_urls(&[
+                "https://server1.com/repo.git",
+                "https://server2.com/repo.git",
+                "https://server3.com/repo.git",
+            ])
+            .with_needed_oids(&["abc123", "def456", "ghi789"])
+            .with_pending_events(true)
+            .url_provides("https://server1.com/repo.git", &["abc123"])
+            .url_provides("https://server2.com/repo.git", &["def456"])
+            .url_provides("https://server3.com/repo.git", &["ghi789"]);
+
+        let throttle_manager = Arc::new(ThrottleManager::new(5, 100));
+
+        // Run sync_identifier
+        let complete = sync_identifier(&mock, "test-repo", &throttle_manager).await;
+
+        // Should return true (sync complete)
+        assert!(complete, "Expected sync to complete after trying all URLs");
+
+        // Should have tried all 3 URLs
+        let fetch_log = mock.fetch_log();
+        assert_eq!(
+            fetch_log.len(),
+            3,
+            "Expected 3 fetch attempts, got: {:?}",
+            fetch_log
+        );
+
+        // All OIDs should now be fetched
+        assert!(
+            mock.current_needed_oids().is_empty(),
+            "Expected all OIDs to be fetched"
+        );
+    }
+
+    #[tokio::test]
+    async fn sync_identifier_enqueues_throttled_domains_when_incomplete() {
+        // Set up mock with URLs from two domains
+        // Only github.com can provide the OID, but it will be throttled
+        let mock = MockSyncContext::new()
+            .with_urls(&[
+                "https://github.com/foo/bar.git",
+                "https://gitlab.com/foo/bar.git",
+            ])
+            .with_needed_oids(&["abc123"])
+            .with_pending_events(true)
+            .url_provides("https://github.com/foo/bar.git", &["abc123"]);
+        // Note: gitlab.com doesn't provide any OIDs
+
+        let throttle_manager = Arc::new(ThrottleManager::new(1, 100));
+
+        // Throttle github.com by starting a request
+        throttle_manager.start_request("github.com");
+
+        // Run sync_identifier
+        let complete = sync_identifier(&mock, "test-repo", &throttle_manager).await;
+
+        // Should return false (sync incomplete - github.com is throttled)
+        assert!(
+            !complete,
+            "Expected sync to be incomplete when required domain is throttled"
+        );
+
+        // Should have tried gitlab.com (not throttled) but it doesn't have the OID
+        let fetch_log = mock.fetch_log();
+        assert_eq!(
+            fetch_log.len(),
+            1,
+            "Expected 1 fetch attempt (gitlab.com), got: {:?}",
+            fetch_log
+        );
+        assert!(
+            fetch_log[0].contains("gitlab.com"),
+            "Expected gitlab.com to be tried first"
+        );
+
+        // OID should still be needed
+        assert!(
+            mock.current_needed_oids().contains("abc123"),
+            "Expected OID to still be needed"
+        );
+
+        // github.com should have the identifier enqueued
+        // We can verify this by checking if github.com is still throttled (it should be,
+        // since the identifier was enqueued but not processed yet)
+        assert!(
+            throttle_manager.is_throttled("github.com"),
+            "Expected github.com to still be throttled"
+        );
+    }
 }