Assume merged diffs are squashed and diff against parent (#446)

crates/local-deployment/src/container.rs

@@ -462,14 +462,12 @@ impl LocalContainerService {
         &self,
         project_repo_path: &Path,
         merge_commit_id: &str,
-        base_branch: &str,
     ) -> Result<futures::stream::BoxStream<'static, Result<Event, std::io::Error>>, ContainerError>
     {
         let diffs = self.git().get_diffs(
             DiffTarget::Commit {
                 repo_path: project_repo_path,
                 commit_sha: merge_commit_id,
-                base_branch,
             },
             None,
         )?;
@@ -481,6 +479,9 @@ impl LocalContainerService {
             let event = LogMsg::JsonPatch(patch).to_sse_event();
             Ok::<_, std::io::Error>(event)
         }))
+        .chain(futures::stream::once(async {
+            Ok::<_, std::io::Error>(LogMsg::Finished.to_sse_event())
+        }))
         .boxed();
 
         Ok(stream)
@@ -847,11 +848,7 @@ impl ContainerService for LocalContainerService {
 
         // Handle merged attempts (static diff)
         if let Some(merge_commit_id) = &task_attempt.merge_commit {
-            return self.create_merged_diff_stream(
-                &project_repo_path,
-                merge_commit_id,
-                &task_attempt.base_branch,
-            );
+            return self.create_merged_diff_stream(&project_repo_path, merge_commit_id);
         }
 
         let task_branch = task_attempt

crates/services/src/services/git.rs

@@ -73,7 +73,6 @@ pub enum DiffTarget<'p> {
     Commit {
         repo_path: &'p Path,
         commit_sha: &'p str,
-        base_branch: &'p str,
     },
 }
 
@@ -253,39 +252,44 @@ impl GitService {
             DiffTarget::Commit {
                 repo_path,
                 commit_sha,
-                base_branch,
             } => {
                 let repo = self.open_repo(repo_path)?;
-                let base_tree = repo
-                    .find_branch(base_branch, BranchType::Local)
-                    .map_err(|_| GitServiceError::BranchNotFound(base_branch.to_string()))?
-                    .get()
-                    .peel_to_commit()?
-                    .tree()?;
 
+                // Resolve commit and its baseline (the parent before the squash landed)
                 let commit_oid = git2::Oid::from_str(commit_sha).map_err(|_| {
                     GitServiceError::InvalidRepository(format!("Invalid commit SHA: {commit_sha}"))
                 })?;
-                let commit_tree = repo.find_commit(commit_oid)?.tree()?;
+                let commit = repo.find_commit(commit_oid)?;
+                let parent = commit.parent(0).map_err(|_| {
+                    GitServiceError::InvalidRepository(
+                        "Commit has no parent; cannot diff a squash merge without a baseline"
+                            .into(),
+                    )
+                })?;
 
-                let mut diff_opts = DiffOptions::new();
+                let parent_tree = parent.tree()?;
+                let commit_tree = commit.tree()?;
+
+                // Diff options
+                let mut diff_opts = git2::DiffOptions::new();
                 diff_opts.include_typechange(true);
 
-                // Add path filtering if specified
+                // Optional path filtering
                 if let Some(paths) = path_filter {
                     for path in paths {
                         diff_opts.pathspec(*path);
                     }
                 }
 
+                // Compute the diff parent -> commit
                 let mut diff = repo.diff_tree_to_tree(
-                    Some(&base_tree),
+                    Some(&parent_tree),
                     Some(&commit_tree),
                     Some(&mut diff_opts),
                 )?;
 
                 // Enable rename detection
-                let mut find_opts = DiffFindOptions::new();
+                let mut find_opts = git2::DiffFindOptions::new();
                 diff.find_similar(Some(&mut find_opts))?;
 
                 self.convert_diff_to_file_diffs(diff, &repo)