fix: diff shows files as deleted when run from subdirectory

src/command/diff/git.rs

@@ -103,7 +103,13 @@ pub fn get_new_content(filename: &str, refs: &DiffRefs, backend: &dyn VcsBackend
             .unwrap_or_default(),
         DiffRefs::WorkingTree => {
             // Read from working tree (actual filesystem)
-            fs::read_to_string(filename).unwrap_or_default()
+            // Resolve path relative to repository root, not current working directory
+            if let Some(repo_root) = backend.repo_root() {
+                let full_path = repo_root.join(filename);
+                fs::read_to_string(&full_path).unwrap_or_default()
+            } else {
+                fs::read_to_string(filename).unwrap_or_default()
+            }
         }
     }
 }
@@ -476,4 +482,33 @@ mod tests {
         let _ = std::env::set_current_dir(&original);
         let _ = fs::remove_dir_all(&dir);
     }
+
+    #[test]
+    fn test_get_new_content_from_subdirectory() {
+        let _lock = crate::vcs::test_utils::cwd_lock()
+            .lock()
+            .unwrap_or_else(|e| e.into_inner());
+        let dir = make_temp_dir("git-diff-subdir");
+        let original = std::env::current_dir().expect("get cwd");
+
+        git(&dir, &["init"]);
+        git(&dir, &["config", "user.email", "test@example.com"]);
+        git(&dir, &["config", "user.name", "Test User"]);
+
+        fs::create_dir(dir.join("src")).expect("create src dir");
+        fs::write(dir.join("src/file.txt"), "original content\n").expect("write file");
+        git(&dir, &["add", "."]);
+        git(&dir, &["commit", "-m", "first"]);
+
+        fs::write(dir.join("src/file.txt"), "modified content\n").expect("modify file");
+
+        // Run diff from subdirectory
+        std::env::set_current_dir(dir.join("src")).expect("change to src dir");
+        let backend = GitBackend::from_cwd().expect("should open repo");
+        let content = get_new_content("src/file.txt", &DiffRefs::WorkingTree, &backend);
+        assert_eq!(content, "modified content\n");
+
+        let _ = std::env::set_current_dir(&original);
+        let _ = fs::remove_dir_all(&dir);
+    }
 }

src/vcs/backend.rs

@@ -131,4 +131,7 @@ pub trait VcsBackend {
 
     /// Get the name of this VCS backend ("git" or "jj").
     fn name(&self) -> &'static str;
+
+    /// Get the root path of the repository (working directory).
+    fn repo_root(&self) -> Option<&Path>;
 }

src/vcs/git.rs

@@ -786,6 +786,10 @@ impl VcsBackend for GitBackend {
     fn name(&self) -> &'static str {
         "git"
     }
+
+    fn repo_root(&self) -> Option<&Path> {
+        self.repo.workdir()
+    }
 }
 
 #[cfg(test)]

src/vcs/jj.rs

@@ -973,6 +973,10 @@ impl VcsBackend for JjBackend {
     fn name(&self) -> &'static str {
         "jj"
     }
+
+    fn repo_root(&self) -> Option<&Path> {
+        Some(&self.workspace_path)
+    }
 }
 
 #[cfg(test)]