feat(tools): support GIF images in view_image (#4438)

Add GIF to the view_image allowlist: map the .gif extension to
image/gif and detect the GIF87a/GIF89a magic bytes so the existing
extension/content cross-check accepts GIFs instead of rejecting them
as an unsupported format. Covered by a new success test.

backend/packages/harness/deerflow/tools/builtins/view_image_tool.py

@@ -22,6 +22,7 @@ _EXTENSION_TO_MIME = {
     ".jpeg": "image/jpeg",
     ".png": "image/png",
     ".webp": "image/webp",
+    ".gif": "image/gif",
 }
 
 
@@ -36,6 +37,8 @@ def _detect_image_mime(image_data: bytes) -> str | None:
         return "image/png"
     if len(image_data) >= 12 and image_data.startswith(b"RIFF") and image_data[8:12] == b"WEBP":
         return "image/webp"
+    if image_data.startswith((b"GIF87a", b"GIF89a")):
+        return "image/gif"
     return None
 
 
@@ -63,7 +66,7 @@ def view_image_tool(
     - For multiple files at once (use present_files instead)
 
     Args:
-        image_path: Absolute /mnt/user-data virtual path to the image file. Common formats supported: jpg, jpeg, png, webp.
+        image_path: Absolute /mnt/user-data virtual path to the image file. Common formats supported: jpg, jpeg, png, webp, gif.
     """
     from deerflow.sandbox.exceptions import SandboxRuntimeError
     from deerflow.sandbox.tools import (

backend/tests/test_view_image_tool.py

@@ -12,6 +12,9 @@ view_image_module = importlib.import_module("deerflow.tools.builtins.view_image_
 
 PNG_BYTES = base64.b64decode("iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg==")
 
+# Minimal 1x1 transparent GIF (starts with the "GIF89a" magic bytes).
+GIF_BYTES = base64.b64decode("R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7")
+
 
 def _make_thread_data(tmp_path: Path) -> dict[str, str]:
     user_data = tmp_path / "threads" / "thread-1" / "user-data"
@@ -73,6 +76,23 @@ def test_view_image_reads_virtual_uploads_path(tmp_path: Path) -> None:
     assert viewed_image["actual_path"] == str(image_path)
 
 
+def test_view_image_reads_gif(tmp_path: Path) -> None:
+    thread_data = _make_thread_data(tmp_path)
+    image_path = Path(thread_data["uploads_path"]) / "animation.gif"
+    image_path.write_bytes(GIF_BYTES)
+
+    result = view_image_tool.func(
+        runtime=_make_runtime(thread_data),
+        image_path="/mnt/user-data/uploads/animation.gif",
+        tool_call_id="tc-gif",
+    )
+
+    assert _message_content(result) == "Successfully read image"
+    viewed_image = result.update["viewed_images"]["/mnt/user-data/uploads/animation.gif"]
+    assert viewed_image["mime_type"] == "image/gif"
+    assert viewed_image["size"] == len(GIF_BYTES)
+
+
 def test_view_image_rejects_spoofed_extension(tmp_path: Path) -> None:
     thread_data = _make_thread_data(tmp_path)
     image_path = Path(thread_data["uploads_path"]) / "not-really.png"