feat(pack): add raw advertise refs and stateless protocol support

- Add raw flag to AdvertiseRefsRequest to enable raw pkt-line output
- Implement advertise_refs_raw function that calls git upload-pack/receive-pack with --advertise-refs
- Add stateless flag to GitProtocolFeatures for HTTP smart protocol support
- Modify upload_pack and receive_pack to accept stateless parameter
- Update command construction to include --stateless-rpc flag when enabled
- Add raw_data field to AdvertiseRefsResponse for raw output
- Update pack cache key computation to include raw service differentiation
- Initialize raw field to false in all request creation calls

pack/advertise_refs.rs

@@ -1,12 +1,15 @@
 use crate::bare::GitBare;
-use crate::error::GitResult;
+use crate::error::{GitError, GitResult};
 use crate::pb::{AdvertiseRefsRequest, AdvertiseRefsResponse, ReferenceAdvertisement};
 
 impl GitBare {
     pub fn advertise_refs(
         &self,
-        _request: AdvertiseRefsRequest,
+        request: AdvertiseRefsRequest,
     ) -> GitResult<AdvertiseRefsResponse> {
+        if request.raw {
+            return self.advertise_refs_raw(&request);
+        }
         let repo = self.gix_repo()?;
         let mut references = Vec::new();
         for r in repo.references()?.all()? {
@@ -52,6 +55,60 @@ impl GitBare {
                 "multi_ack".into(),
                 "symref=HEAD".into(),
             ],
+            raw_data: Vec::new(),
+        })
+    }
+
+    /// Return raw pkt-line output from git upload-pack/receive-pack --advertise-refs.
+    /// Used by transparent proxies (gitshell) that forward bytes verbatim to git clients.
+    fn advertise_refs_raw(
+        &self,
+        request: &AdvertiseRefsRequest,
+    ) -> GitResult<AdvertiseRefsResponse> {
+        let bare_dir_str = self.bare_dir.to_string_lossy().into_owned();
+        let stateless = request.protocol.as_ref().is_some_and(|p| p.stateless);
+
+        // Default to upload-pack if service is unspecified
+        let subcommand = if request.service == "git-receive-pack" {
+            "receive-pack"
+        } else {
+            "upload-pack"
+        };
+
+        let mut args: Vec<String> = vec![
+            "--git-dir".into(),
+            bare_dir_str,
+            subcommand.into(),
+            "--advertise-refs".into(),
+        ];
+        if stateless {
+            args.push("--stateless-rpc".into());
+        }
+
+        let result = duct::cmd("git", &args)
+            .stdout_capture()
+            .stderr_capture()
+            .unchecked()
+            .run()?;
+
+        if !result.status.success() {
+            return Err(GitError::CommandFailed {
+                status_code: result.status.code(),
+                stderr: String::from_utf8_lossy(&result.stderr).into_owned(),
+            });
+        }
+
+        tracing::debug!(
+            raw_len = result.stdout.len(),
+            service = %request.service,
+            stateless = stateless,
+            "advertise_refs raw output"
+        );
+
+        Ok(AdvertiseRefsResponse {
+            references: Vec::new(),
+            capabilities: Vec::new(),
+            raw_data: result.stdout,
         })
     }
 }