Enhance git integration and optimize change detection in ServeSession

- Introduced a new function to retrieve the current HEAD commit SHA, allowing for better tracking of changes in the git repository.
- Updated the `git_changed_files` function to accept an initial HEAD parameter, improving the accuracy of change detection.
- Modified `ServeSession` to store the initial HEAD commit SHA at session start, ensuring committed changes are reflected in the auto-selection logic.
- Enhanced tests to verify that committed changes after session start are correctly identified and included in the change tracking.

These changes aim to improve the synchronization process with git and enhance the user experience by ensuring accurate change detection.

src/serve_session.rs

@@ -122,6 +122,11 @@ pub struct ServeSession {
     /// Root of the git repository, if the project is inside one.
     /// Computed once at session start for use by auto-staging.
     git_repo_root: Option<std::path::PathBuf>,
+
+    /// HEAD commit SHA at the time this serve session started.
+    /// Used as diff baseline so that files committed after session start
+    /// still appear in `changedIds` for auto-select defaults.
+    initial_head_commit: Option<String>,
 }
 
 /// Collect all filesystem paths reachable from the project tree's `$path`
@@ -351,6 +356,9 @@ impl ServeSession {
         };
 
         let git_repo_root = crate::git::git_repo_root(root_project.folder_location());
+        let initial_head_commit = git_repo_root
+            .as_deref()
+            .and_then(crate::git::git_head_commit);
 
         log::trace!("Starting ChangeProcessor");
         let change_processor = ChangeProcessor::start(
@@ -378,6 +386,7 @@ impl ServeSession {
             suppressed_paths: Some(suppressed_paths),
             ref_path_index: Some(ref_path_index),
             git_repo_root,
+            initial_head_commit,
         })
     }
 
@@ -404,6 +413,7 @@ impl ServeSession {
             suppressed_paths: None,
             ref_path_index: None,
             git_repo_root: None,
+            initial_head_commit: None,
         })
     }
 
@@ -492,6 +502,10 @@ impl ServeSession {
         self.git_repo_root.as_deref()
     }
 
+    pub fn initial_head_commit(&self) -> Option<&str> {
+        self.initial_head_commit.as_deref()
+    }
+
     pub fn root_project(&self) -> &Project {
         &self.root_project
     }