fix(video-surfer): apply extract_audio path guards to save_screenshot

[Dev Oskii (Oskii)]

What

VideoSurfer's extract_audio already refuses a URL video_path and an audio_output_path that resolves outside the current working directory. save_screenshot takes the same kinds of paths and did not run those checks. An agent-chosen output_path such as ../escaped.png (or an absolute path outside cwd) is passed straight to cv2.imwrite. A URL video_path is passed straight to cv2.VideoCapture.

On main at 027ecf0:

# extract_audio
if re.match(r"^[a-zA-Z][a-zA-Z0-9+\-.]*://", video_path):
    raise ValueError("video_path must be a local file path, not a URL.")
# ...
if not output_real.startswith(cwd + os.sep) and output_real != cwd:
    raise ValueError("audio_output_path must be within the current working directory.")

# save_screenshot
cap = cv2.VideoCapture(video_path)
# ...
cv2.imwrite(output_path, frame)

Default VideoSurfer includes save_screenshot in its tool list. After this change, save_screenshot uses the same two helpers as extract_audio.

Why

I was reading VideoSurfer's tools because extract_audio already documents an SSRF and path-traversal guard. I expected save_screenshot to share that jail. It does not. I confirmed the three new save_screenshot tests fail on 027ecf0 (they never raise the cwd/URL ValueError) and pass with this patch.

How

Move the URL and cwd checks into video_surfer/_path_guards.py. Call them from extract_audio (same behaviour, same error strings) and from save_screenshot before OpenCV runs.

Testing

python3 -m pytest python/packages/autogen-ext/tests/agents/test_video_surfer_path_guards.py -q

5 passed. The three save_screenshot cases fail on 027ecf0 and pass with the patch. The two extract_audio cases already passed on 027ecf0.

The test file stubs cv2, ffmpeg, and whisper so it runs without the video-surfer extra.

[Dev Oskii (Oskii)]

@microsoft-github-policy-service agree

[Dev Oskii (Oskii)]

CLA is signed. GitHub Actions is still waiting on maintainer approval for first-time contributor workflows (Checks and the other pull_request jobs). I cannot approve those from this account.

Once the workflows run I can fix any failures. A review would also unblock merge: save_screenshot now uses the same URL and cwd checks as extract_audio, with tests for both.