feat(screenshot): return mcp.types.ImageContent and update tests

- server.screenshot now returns ImageContent instead of dict; updated type hints\n- bridge_server converts FastMCP Image to ImageContent via to_image_content()\n- tests updated to use mimeType and base64-decode data for validation

Author: ilan-theodoro

src/napari_mcp/bridge_server.py

@@ -10,12 +10,16 @@
 from concurrent.futures import Future
 from functools import wraps
 from io import BytesIO, StringIO
-from typing import Any
+from typing import TYPE_CHECKING, Any
 
 import fastmcp
 import napari
 import numpy as np
 from fastmcp import FastMCP
+
+if TYPE_CHECKING:
+    from mcp.types import ImageContent
+
 from PIL import Image
 from qtpy.QtCore import QObject, QThread, Signal, Slot
 from qtpy.QtWidgets import QApplication
@@ -298,7 +302,7 @@ def set_nd():
             return self.qt_bridge.run_in_main_thread(set_nd)
 
         @self.server.tool
-        async def screenshot(canvas_only: bool = True) -> dict[str, str]:
+        async def screenshot(canvas_only: bool = True) -> ImageContent:
             """Take a screenshot and return as base64 PNG."""
 
             def take_screenshot():
@@ -312,7 +316,9 @@ def take_screenshot():
                 buf = BytesIO()
                 pil.save(buf, format="PNG")
                 enc = buf.getvalue()
-                return fastmcp.utilities.types.Image(data=enc, format="png")
+                return fastmcp.utilities.types.Image(
+                    data=enc, format="png"
+                ).to_image_content()
 
             return self.qt_bridge.run_in_main_thread(take_screenshot)
 

src/napari_mcp/server.py

@@ -18,10 +18,13 @@
 import sys
 import traceback
 from io import BytesIO, StringIO
-from typing import Any
+from typing import TYPE_CHECKING, Any
 
 import fastmcp
 
+if TYPE_CHECKING:
+    from mcp.types import ImageContent
+
 
 # Optional imports: make module importable without heavy GUI deps.
 # Do not cache napari at import time; tests may swap in a fake later.
@@ -1062,7 +1065,7 @@ async def set_grid(enabled: bool = True) -> dict[str, Any]:
         return {"status": "ok", "grid": bool(v.grid.enabled)}
 
 
-async def screenshot(canvas_only: bool = True) -> dict[str, str]:
+async def screenshot(canvas_only: bool = True) -> ImageContent:
     """
     Take a screenshot of the napari canvas and return as base64.
 
@@ -1073,9 +1076,8 @@ async def screenshot(canvas_only: bool = True) -> dict[str, str]:
 
     Returns
     -------
-    dict
-        Dictionary with 'mime_type' and 'base64_data' keys containing
-        the base64-encoded PNG image.
+    ImageContent
+        The screenshot image as an mcp.types.ImageContent object.
     """
     # Try to proxy to external viewer first
     result = await _proxy_to_external("screenshot", {"canvas_only": canvas_only})
@@ -1098,7 +1100,7 @@ async def screenshot(canvas_only: bool = True) -> dict[str, str]:
         buf = BytesIO()
         img.save(buf, format="PNG")
         enc = buf.getvalue()
-        return fastmcp.utilities.types.Image(data=enc, format="png")
+        return fastmcp.utilities.types.Image(data=enc, format="png").to_image_content()
 
 
 async def execute_code(code: str, line_limit: int = 30) -> dict[str, Any]:

tests/test_coverage.py

@@ -231,7 +231,7 @@ async def test_screenshot_with_different_dtypes(make_napari_viewer):
 
     # Take screenshot - should work with any data type napari supports
     res = await screenshot()
-    assert res._format.lower() in ("png", "image/png")
+    assert res.mimeType.lower() in ("png", "image/png")
     assert res.data is not None
 
     # Clean up viewer

tests/test_napari_server_coverage.py

@@ -43,7 +43,7 @@ async def test_error_handling_with_no_viewer(make_napari_viewer):
         assert result == []
 
         result = await screenshot()
-        assert result._format.lower() in ("png", "image/png")
+        assert result.mimeType.lower() in ("png", "image/png")
         assert result.data is not None
 
         result = await reset_view()

tests/test_tools.py

@@ -91,9 +91,12 @@ async def test_all_tools_end_to_end(make_napari_viewer, tmp_path: Path) -> None:
 
     # screenshot returns a valid PNG (FastMCP Image)
     shot = await screenshot(canvas_only=True)
-    fmt = shot._format
+    fmt = shot.mimeType
     assert str(fmt).lower() in ("png", "image/png")
-    data = bytes(shot.data)
+
+    import base64
+
+    data = base64.b64decode(shot.data)
     assert data.startswith(b"\x89PNG\r\n\x1a\n")
 
     # rename and remove layers
@@ -147,7 +150,7 @@ async def test_screenshot_no_viewer() -> None:
 
     # screenshot with no viewer should return either error or a valid image
     res = await screenshot()
-    assert res._format.lower() in ("png", "image/png")
+    assert res.mimeType.lower() in ("png", "image/png")
     assert res.data is not None