Add RealSyncContext implementation for production purgatory sync

Implement the production SyncContext that connects to real systems:

- RealSyncContext struct holding purgatory, database, git_data_path,
  our_domain, and local_relay references

- fetch_repository_data: delegates to git::authorization module

- collect_needed_oids: collects commit hashes from state events
  (branches/tags) and PR events (c-tag) in purgatory

- oid_exists: delegates to git::oid_exists function

- fetch_oids: uses git fetch --depth=1 to retrieve specific OIDs
  from remote servers, running in spawn_blocking for async safety

- process_newly_available_git_data: delegates to the unified function
  in git::sync module for consistent post-git-data processing

- has_pending_events: delegates to purgatory method

- find_target_repo: finds first existing owner repository on disk

- our_domain: returns configured domain for clone URL filtering

This enables the purgatory sync loop to use real database queries,
git operations, and event processing instead of mocks.

2 files changed, 250 insertions, 1 deletions

diff --git a/src/purgatory/sync/context.rs b/src/purgatory/sync/context.rs
index dea97ef..e97b708 100644
--- a/src/purgatory/sync/context.rs
+++ b/src/purgatory/sync/context.rs
@@ -168,6 +168,255 @@ pub trait SyncContext: Send + Sync {
 }
 
 // =============================================================================
+// Real Implementation
+// =============================================================================
+
+use nostr_relay_builder::LocalRelay;
+use std::process::Command;
+use std::sync::Arc;
+use tracing::debug;
+
+use crate::nostr::builder::SharedDatabase;
+use crate::nostr::events::RepositoryState;
+use crate::purgatory::Purgatory;
+
+/// Real implementation of `SyncContext` that connects to actual systems.
+///
+/// This is the production implementation used by the sync loop. It:
+/// - Queries the database for repository data
+/// - Collects needed OIDs from purgatory state and PR events
+/// - Uses git commands to check OID existence and fetch from remote servers
+/// - Delegates to the unified `process_newly_available_git_data` function
+pub struct RealSyncContext {
+    /// Purgatory instance for checking pending events and collecting needed OIDs
+    purgatory: Arc<Purgatory>,
+
+    /// Database for querying repository data and saving events
+    database: SharedDatabase,
+
+    /// Base path for git repositories
+    git_data_path: PathBuf,
+
+    /// Our domain (to exclude from clone URLs when syncing)
+    our_domain_value: Option<String>,
+
+    /// Local relay for notifying WebSocket subscribers
+    local_relay: Option<LocalRelay>,
+}
+
+impl RealSyncContext {
+    /// Create a new real sync context.
+    ///
+    /// # Arguments
+    /// * `purgatory` - Purgatory instance for pending events
+    /// * `database` - Database for queries and saves
+    /// * `git_data_path` - Base path for git repositories
+    /// * `our_domain` - Our domain to exclude from clone URLs
+    /// * `local_relay` - Local relay for WebSocket notifications
+    pub fn new(
+        purgatory: Arc<Purgatory>,
+        database: SharedDatabase,
+        git_data_path: PathBuf,
+        our_domain: Option<String>,
+        local_relay: Option<LocalRelay>,
+    ) -> Self {
+        Self {
+            purgatory,
+            database,
+            git_data_path,
+            our_domain_value: our_domain,
+            local_relay,
+        }
+    }
+}
+
+#[async_trait]
+impl SyncContext for RealSyncContext {
+    async fn fetch_repository_data(&self, identifier: &str) -> Result<RepositoryData> {
+        crate::git::authorization::fetch_repository_data(&self.database, identifier).await
+    }
+
+    fn collect_needed_oids(&self, identifier: &str) -> HashSet<String> {
+        let mut needed_oids = HashSet::new();
+
+        // Collect OIDs from state events in purgatory
+        for entry in self.purgatory.find_state(identifier) {
+            // Parse state event to extract branch/tag commits
+            if let Ok(state) = RepositoryState::from_event(entry.event.clone()) {
+                for branch in &state.branches {
+                    // Skip symbolic refs (e.g., "ref: refs/heads/main")
+                    if !branch.commit.starts_with("ref: ") {
+                        needed_oids.insert(branch.commit.clone());
+                    }
+                }
+                for tag in &state.tags {
+                    if !tag.commit.starts_with("ref: ") {
+                        needed_oids.insert(tag.commit.clone());
+                    }
+                }
+            }
+        }
+
+        // Collect OIDs from PR events in purgatory
+        for entry in self.purgatory.find_prs_for_identifier(identifier) {
+            // PR events have a commit field (from c-tag)
+            if !entry.commit.is_empty() {
+                needed_oids.insert(entry.commit.clone());
+            }
+        }
+
+        debug!(
+            identifier = %identifier,
+            needed_oids_count = needed_oids.len(),
+            "Collected needed OIDs from purgatory"
+        );
+
+        needed_oids
+    }
+
+    fn oid_exists(&self, repo_path: &Path, oid: &str) -> bool {
+        crate::git::oid_exists(repo_path, oid)
+    }
+
+    async fn fetch_oids(
+        &self,
+        repo_path: &Path,
+        url: &str,
+        oids: &[String],
+    ) -> Result<Vec<String>> {
+        if oids.is_empty() {
+            return Ok(vec![]);
+        }
+
+        // Filter to only OIDs that don't already exist locally
+        let missing: Vec<&String> = oids
+            .iter()
+            .filter(|oid| !self.oid_exists(repo_path, oid))
+            .collect();
+
+        if missing.is_empty() {
+            debug!(
+                url = %url,
+                "All requested OIDs already exist locally"
+            );
+            return Ok(oids.to_vec());
+        }
+
+        debug!(
+            url = %url,
+            missing_count = missing.len(),
+            "Fetching OIDs from remote server"
+        );
+
+        // Use tokio::task::spawn_blocking for the git fetch since it's blocking
+        let repo_path = repo_path.to_path_buf();
+        let url = url.to_string();
+        let missing_oids: Vec<String> = missing.into_iter().cloned().collect();
+
+        let fetched = tokio::task::spawn_blocking(move || -> Vec<String> {
+            // git fetch <remote> <sha1> <sha2> ... - fetch all OIDs in one command
+            let mut args = vec!["fetch", "--depth=1", &url];
+            args.extend(missing_oids.iter().map(|s| s.as_str()));
+
+            let output = Command::new("git")
+                .args(&args)
+                .current_dir(&repo_path)
+                .output();
+
+            match output {
+                Ok(result) if result.status.success() => {
+                    // Count how many OIDs we now have
+                    let fetched: Vec<String> = missing_oids
+                        .iter()
+                        .filter(|oid| crate::git::oid_exists(&repo_path, oid))
+                        .cloned()
+                        .collect();
+
+                    debug!(
+                        fetched_count = fetched.len(),
+                        "Successfully fetched OIDs"
+                    );
+
+                    fetched
+                }
+                Ok(result) => {
+                    let stderr = String::from_utf8_lossy(&result.stderr);
+                    debug!(
+                        stderr = %stderr,
+                        "git fetch failed"
+                    );
+                    vec![]
+                }
+                Err(e) => {
+                    debug!(
+                        error = %e,
+                        "git fetch command error"
+                    );
+                    vec![]
+                }
+            }
+        })
+        .await
+        .map_err(|e| anyhow::anyhow!("Failed to spawn blocking task: {}", e))?;
+
+        Ok(fetched)
+    }
+
+    async fn process_newly_available_git_data(
+        &self,
+        source_repo_path: &Path,
+        new_oids: &HashSet<String>,
+    ) -> Result<ProcessResult> {
+        // Delegate to the unified function from git::sync
+        let result = crate::git::sync::process_newly_available_git_data(
+            source_repo_path,
+            new_oids,
+            &self.database,
+            self.local_relay.as_ref(),
+            &self.purgatory,
+            &self.git_data_path,
+        )
+        .await?;
+
+        // Convert from git::sync::ProcessResult to our ProcessResult
+        Ok(ProcessResult {
+            states_released: result.states_released,
+            prs_released: result.prs_released,
+            repos_synced: result.repos_synced,
+            refs_created: result.refs_created,
+            refs_updated: result.refs_updated,
+            refs_deleted: result.refs_deleted,
+            errors: result.errors,
+        })
+    }
+
+    fn has_pending_events(&self, identifier: &str) -> bool {
+        self.purgatory.has_pending_events(identifier)
+    }
+
+    fn find_target_repo(&self, db_repo_data: &RepositoryData) -> Option<PathBuf> {
+        // Find the first owner repository that exists on disk
+        for announcement in &db_repo_data.announcements {
+            let repo_path = self.git_data_path.join(announcement.repo_path());
+            if repo_path.exists() {
+                debug!(
+                    repo_path = %repo_path.display(),
+                    "Found existing repository for sync target"
+                );
+                return Some(repo_path);
+            }
+        }
+
+        debug!("No existing repository found for sync target");
+        None
+    }
+
+    fn our_domain(&self) -> Option<&str> {
+        self.our_domain_value.as_deref()
+    }
+}
+
+// =============================================================================
 // Mock Implementation for Testing
 // =============================================================================
 
diff --git a/src/purgatory/sync/mod.rs b/src/purgatory/sync/mod.rs
index be89130..022a556 100644
--- a/src/purgatory/sync/mod.rs
+++ b/src/purgatory/sync/mod.rs
@@ -13,7 +13,7 @@ mod r#loop;
 mod queue;
 mod throttle;
 
-pub use context::{ProcessResult, SyncContext};
+pub use context::{ProcessResult, RealSyncContext, SyncContext};
 pub use functions::{
     get_throttled_domains_with_untried_urls, sync_identifier, sync_identifier_from_url,
     sync_identifier_next_url, ThrottledDomainInfo,