Address PR review comments #8, #14, #16

- Fix #8: Update docstring to clarify dtype casting behavior (may clip)
- Fix #14: Add OSError handling in load_flatfield for file access errors
- Fix #16: Sync flatfield checkbox state with loaded/cleared status

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: hongquanli

gui/app.py

@@ -1221,6 +1221,8 @@ def on_file_dropped(self, file_path):
         self.view_flatfield_button.setEnabled(False)
         self.clear_flatfield_button.setEnabled(False)
         self.save_flatfield_button.setEnabled(False)
+        # Uncheck flatfield correction when no flatfield is loaded
+        self.flatfield_checkbox.setChecked(False)
 
         # Auto-load existing flatfield if present
         flatfield_path = path.parent / f"{path.stem}_flatfield.npy"
@@ -1340,6 +1342,8 @@ def on_flatfield_dropped(self, file_path):
             )
             self.view_flatfield_button.setEnabled(True)
             self.clear_flatfield_button.setEnabled(True)
+            # Enable flatfield correction when successfully loaded
+            self.flatfield_checkbox.setChecked(True)
             self.log(f"Loaded flatfield from {file_path}: {self.flatfield.shape}")
         except Exception as e:
             self.flatfield_status.setText(f"Load failed: {e}")

src/tilefusion/flatfield.py

@@ -120,7 +120,10 @@ def apply_flatfield(
     Returns
     -------
     corrected : ndarray
-        Corrected tile with shape (C, Y, X), same dtype as input.
+        Corrected tile with shape (C, Y, X), cast back to the input dtype.
+        Note: Values are computed in float then cast to the original dtype,
+        which may result in clipping for values outside the dtype's valid
+        range (e.g., negative values clipped to 0 for unsigned types).
 
     Raises
     ------
@@ -248,10 +251,16 @@ def load_flatfield(path: Path) -> Tuple[np.ndarray, Optional[np.ndarray]]:
 
     Raises
     ------
+    OSError
+        If the file cannot be read (not found, permission denied, etc.).
     ValueError
         If the file format is invalid (not a dictionary with 'flatfield' key).
     """
-    loaded = np.load(path, allow_pickle=True)
+    try:
+        loaded = np.load(path, allow_pickle=True)
+    except OSError as exc:
+        raise OSError(f"Cannot read flatfield file '{path}': {exc}") from exc
+
     try:
         data = loaded.item()
     except (AttributeError, ValueError) as exc: