Resolve file paths relative to repo root

src/command/diff/git.rs

@@ -102,8 +102,12 @@ pub fn get_new_content(filename: &str, refs: &DiffRefs, backend: &dyn VcsBackend
             .get_file_content_at_ref(to, Path::new(filename))
             .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
+            let full_path = backend
+                .get_repository_root()
+                .map(|root| root.join(filename))
+                .unwrap_or_else(|_| filename.into());
+            fs::read_to_string(full_path).unwrap_or_default()
         }
     }
 }
@@ -476,4 +480,55 @@ mod tests {
         let _ = std::env::set_current_dir(&original);
         let _ = fs::remove_dir_all(&dir);
     }
+
+    #[test]
+    fn test_load_file_diffs_from_subdirectory() {
+        use crate::vcs::test_utils::cwd_lock;
+
+        let _lock = cwd_lock().lock().unwrap_or_else(|e| e.into_inner());
+        let dir = make_temp_dir("git-subdir-diff");
+        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"]);
+
+        // Create nested structure
+        fs::create_dir_all(dir.join("src")).expect("create subdir");
+        fs::write(dir.join("src/file.txt"), "initial\n").expect("write file");
+        git(&dir, &["add", "."]);
+        git(&dir, &["commit", "-m", "init"]);
+
+        // Modify file (unstaged change)
+        fs::write(dir.join("src/file.txt"), "modified\n").expect("modify file");
+
+        // Change to subdirectory (simulating running lumen from subdir)
+        std::env::set_current_dir(dir.join("src")).expect("set cwd to subdir");
+
+        let backend = GitBackend::new(Path::new("."))
+            .expect("should open repo from subdir");
+
+        let options = super::DiffOptions {
+            reference: None,
+            pr: None,
+            file: None,
+            watch: false,
+            theme: None,
+            stacked: false,
+        };
+
+        let diffs = load_file_diffs(&options, &backend);
+
+        assert_eq!(diffs.len(), 1, "should have 1 changed file");
+        assert_eq!(diffs[0].filename, "src/file.txt");
+        assert_eq!(
+            diffs[0].status,
+            FileStatus::Modified,
+            "file should be modified, not deleted"
+        );
+        assert_eq!(diffs[0].new_content, "modified\n", "should read new content");
+
+        let _ = std::env::set_current_dir(&original);
+        let _ = fs::remove_dir_all(&dir);
+    }
 }

src/vcs/backend.rs

@@ -129,6 +129,9 @@ pub trait VcsBackend {
         to: &str,
     ) -> Result<Vec<StackedCommitInfo>, VcsError>;
 
+    /// Get the root path of the repository working directory.
+    fn get_repository_root(&self) -> Result<std::path::PathBuf, VcsError>;
+
     /// Get the name of this VCS backend ("git" or "jj").
     fn name(&self) -> &'static str;
 }

src/vcs/git.rs

@@ -783,6 +783,13 @@ impl VcsBackend for GitBackend {
         Ok(commits)
     }
 
+    fn get_repository_root(&self) -> Result<std::path::PathBuf, VcsError> {
+        self.repo
+            .workdir()
+            .map(|p| p.to_path_buf())
+            .ok_or_else(|| VcsError::Other("bare repository has no working directory".to_string()))
+    }
+
     fn name(&self) -> &'static str {
         "git"
     }
@@ -1653,4 +1660,39 @@ mod tests {
         let _ = std::env::set_current_dir(&original);
         let _ = fs::remove_dir_all(&dir);
     }
+
+    #[test]
+    fn test_get_repository_root_from_subdirectory() {
+        use crate::vcs::test_utils::{cwd_lock, git, make_temp_dir};
+        use std::fs;
+
+        let _lock = cwd_lock().lock().unwrap_or_else(|e| e.into_inner());
+        let dir = make_temp_dir("git-repo-root");
+        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_all(dir.join("deep/nested")).expect("create subdirs");
+        fs::write(dir.join("README.md"), "hello\n").expect("write readme");
+        git(&dir, &["add", "."]);
+        git(&dir, &["commit", "-m", "init"]);
+
+        // Change to nested subdirectory
+        std::env::set_current_dir(dir.join("deep/nested")).expect("set cwd");
+
+        let backend = GitBackend::new(Path::new(".")).expect("should discover repo");
+        let root = backend.get_repository_root().expect("should get repo root");
+
+        // Root should be the original repo dir, not the subdirectory
+        assert_eq!(
+            root.canonicalize().unwrap(),
+            dir.canonicalize().unwrap(),
+            "repo root should match original dir"
+        );
+
+        let _ = std::env::set_current_dir(&original);
+        let _ = fs::remove_dir_all(&dir);
+    }
 }

src/vcs/jj.rs

@@ -970,6 +970,10 @@ impl VcsBackend for JjBackend {
         })
     }
 
+    fn get_repository_root(&self) -> Result<std::path::PathBuf, VcsError> {
+        Ok(self.workspace.workspace_root().to_path_buf())
+    }
+
     fn name(&self) -> &'static str {
         "jj"
     }