mcptoolset: non-text tool-result content blocks are silently dropped (EmbeddedResource, ResourceLink, Image, Audio) #1391

Summary

tool/mcptoolset/tool.go's result conversion in mcpTool.Run keeps only *mcp.TextContent blocks. Every other content-block class — EmbeddedResource, ResourceLink, ImageContent, AudioContent — is silently discarded:

textResponse := strings.Builder{}
for _, c := range res.Content {
    textContent, ok := c.(*mcp.TextContent)
    if !ok {
        continue
    }
    ...
}

The same text-only loop is used for the IsError path, and when res.StructuredContent is non-nil the content blocks are ignored entirely.

Real-world impact

GitHub's official MCP server (github/github-mcp-server, also the hosted api.githubcopilot.com endpoints) returns get_file_contents file bodies as an EmbeddedResource block alongside a status-line TextContent (pkg/utils/result.go NewToolResultResource). Through mcptoolset, the model therefore receives only:

successfully downloaded text file (SHA: …)

with no file content at all — the agent is effectively blind to every file it reads, with no error or indication anything was dropped. Directory listings (plain text) survive, which makes the loss non-obvious. Files ≥ 1MB come back as ResourceLink, also dropped.

Related: #1352 covers the "no text content in tool response" error, which is what a result consisting only of non-text blocks currently produces — the two issues are adjacent but distinct.

Suggested behavior

At minimum, flatten EmbeddedResource with textual content (Resource.Text, or Resource.Blob with a text-like MIME type) into the text output, and represent ResourceLink/binary resources legibly (URI + MIME + size) rather than dropping them. Ideally, image/audio blocks would map to genai inlineData parts.

Workaround

Supplying Config.Client with a custom *mcp.Client carrying an AddSendingMiddleware that rewrites EmbeddedResource/ResourceLink blocks into TextContent before the conversion runs restores the content losslessly. Happy to upstream a PR along those lines if useful.

Observed on v2.2.0; main is currently identical for this file.