Description

When an MCP tool returns ImageContent in its response (e.g., screenshot tools, vision tools), Hermes's mcp_tool.py only processes TextContent blocks. ImageContent blocks are silently dropped, resulting in missing visual output and no indication to the user that an image was returned.

Root Cause

In mcp_tool.py, the response handling loop only checks for hasattr(block, "text"):

for block in (result.content or []):
    if hasattr(block, "text"):
        parts.append(block.text)

Per the MCP spec, tool results can contain ContentBlock objects of types:

• TextContent (type="text") — handled ✓
• ImageContent (type="image") — NOT handled ✗
• EmbeddedResource — NOT handled ✗

When an MCP tool like Playwright's browser_take_screenshot or Anthropic's computer_use returns an image, the ImageContent block has data (base64) and mimeType attributes instead of text. These blocks pass the hasattr(block, "text") check (they have a default text="" attribute) but block.text is empty, so they get skipped silently.

Suggested Fix

Add handling for ImageContent blocks in the response loop:

for block in (result.content or []):
    if hasattr(block, "text") and block.text:
        parts.append(block.text)
    elif hasattr(block, "data") and hasattr(block, "mimeType"):
        # ImageContent — save to disk and reference in text
        import base64, uuid
        img_bytes = base64.b64decode(block.data)
        fpath = os.path.join(hermes_home, "image_cache", f"mcp-img-{uuid.uuid4().hex[:8]}.png")
        with open(fpath, "wb") as f:
            f.write(img_bytes)
        parts.append(f"[MCP tool returned an image: {fpath}]")

This saves the image to disk and includes a file path reference so the agent can process it.

Environment

• Hermes: v0.9.0
• Affects: all platforms
• Commonly triggered by: Playwright MCP (screenshots), computer-use-mcp (screenshots), any MCP tool returning visual output

Impact

Without this fix, any MCP tool that returns visual output (screenshots, charts, diagrams) appears to return nothing, making vision-related MCP tools unusable.