fix: canonicalize_path for non-existent files

The path canonicalization was inconsistent when a file didn't exist
at snapshot time but was created later. Now we canonicalize the parent
directory and append the filename, ensuring consistent path lookups
across macOS/Windows/Linux.

Author: Factory Bot

cortex-engine/src/turn_diff_tracker.rs

@@ -653,7 +653,23 @@ impl TurnDiffTracker {
     }
 
     fn canonicalize_path(&self, path: &Path) -> PathBuf {
-        dunce::canonicalize(path).unwrap_or_else(|_| path.to_path_buf())
+        // Try to canonicalize the full path first
+        if let Ok(canonical) = dunce::canonicalize(path) {
+            return canonical;
+        }
+
+        // If that fails (file doesn't exist), canonicalize the parent and append filename
+        // This ensures consistent paths even for non-existent files
+        if let Some(parent) = path.parent() {
+            if let Ok(canonical_parent) = dunce::canonicalize(parent) {
+                if let Some(filename) = path.file_name() {
+                    return canonical_parent.join(filename);
+                }
+            }
+        }
+
+        // Fallback to the original path
+        path.to_path_buf()
     }
 
     /// Find the git worktree root for a path.