MCPToolWrapper.execute only handled TextContent; every other block was
rendered with str(block). An MCP ImageContent block therefore became a
large base64 string embedded in the tool result, which (a) was truncated
by max_tool_result_chars, corrupting the data, and (b) could never reach a
channel because it was plain text, not an image artifact.
Decode ImageContent (and EmbeddedResource blobs with an image/* MIME type)
and persist them via store_generated_image_artifact, returning the same
compact {artifacts, next_step} JSON the built-in image_generation tool
produces. The base64 stays out of the model context; the model delivers the
saved file via the message tool's media parameter.
codedragonandXubin Ren
67ce6822ca