Add Git protocol v2 support to fix modern git client compatibility

Modern git clients (2.51.0+) default to protocol v2 and send the
Git-Protocol header. The server must pass this to git processes via
the GIT_PROTOCOL environment variable for proper negotiation.

Changes:
- Extract Git-Protocol header in HTTP layer (src/http/mod.rs)
- Pass git_protocol parameter through all handler functions
- Set GIT_PROTOCOL env var when spawning git subprocesses
- Update all tests to pass None for backward compatibility

This fixes hangs/timeouts when modern git clients connect to the server.

Fixes issue discovered in work/2025-01-07-pr-clone-tag-sync-investigation.md

1 files changed, 10 insertions, 2 deletions

diff --git a/src/git/subprocess.rs b/src/git/subprocess.rs
index 2d9a981..acee726 100644
--- a/src/git/subprocess.rs
+++ b/src/git/subprocess.rs
@@ -22,10 +22,12 @@ impl GitSubprocess {
     /// * `service` - The Git service (upload-pack or receive-pack)
     /// * `repo_path` - Path to the bare Git repository
     /// * `advertise` - If true, run with --advertise-refs flag
+    /// * `git_protocol` - Optional Git protocol version (e.g., "version=2")
     pub fn spawn(
         service: GitService,
         repo_path: impl AsRef<Path>,
         advertise: bool,
+        git_protocol: Option<&str>,
     ) -> std::io::Result<Self> {
         let repo_path = repo_path.as_ref();
 
@@ -52,6 +54,12 @@ impl GitSubprocess {
         cmd.stdout(Stdio::piped());
         cmd.stderr(Stdio::piped());
 
+        // Set GIT_PROTOCOL environment variable if provided
+        // This enables Git protocol v2 support for modern git clients
+        if let Some(protocol) = git_protocol {
+            cmd.env("GIT_PROTOCOL", protocol);
+        }
+
         let child = cmd.spawn()?;
 
         Ok(Self { child })
@@ -118,7 +126,7 @@ mod tests {
     #[tokio::test]
     async fn test_spawn_upload_pack_advertise() {
         let repo = create_bare_repo();
-        let mut proc = GitSubprocess::spawn(GitService::UploadPack, repo.path(), true)
+        let mut proc = GitSubprocess::spawn(GitService::UploadPack, repo.path(), true, None)
             .expect("Failed to spawn git");
 
         // Should have spawned successfully
@@ -132,7 +140,7 @@ mod tests {
     #[tokio::test]
     async fn test_spawn_receive_pack() {
         let repo = create_bare_repo();
-        let mut proc = GitSubprocess::spawn(GitService::ReceivePack, repo.path(), false)
+        let mut proc = GitSubprocess::spawn(GitService::ReceivePack, repo.path(), false, None)
             .expect("Failed to spawn git");
 
         assert!(proc.stdout().is_some());