fix(mcp): materialize ResourceLink/EmbeddedResource/Audio blocks instead of dropping them (salvage #64061) - #64556
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…ead of dropping them MCP tool results with non-image binary resources (PDFs, archives, office docs) were silently dropped: the success path only handled TextContent and ImageContent, so a PDF-returning MCP tool appeared to return metadata only. - EmbeddedResource blob contents are decoded (50MB cap), materialized into the Hermes document cache via cache_document_from_bytes (sanitized filename, traversal-safe), and surfaced as a local-path marker the agent can read with file/terminal tools. - EmbeddedResource text contents are inlined directly. - ResourceLink blocks preserve the URI and point the agent at the server's read_resource tool; no arbitrary network fetch outside the MCP session. - AudioContent blocks are cached via cache_audio_from_bytes as MEDIA: tags. - read_resource blob contents are materialized the same way instead of returning '[binary data, N bytes]'. - Unsupported blocks are logged instead of silently discarded. - Existing ImageContent MEDIA: behavior unchanged. Reported by an enterprise customer; reproduced against an HTTP MCP server returning application/pdf resources.
…e text in isError path Follow-ups on top of #64061's salvage: - ResourceLink markers now point at mcp__<server>__read_resource (the actual registered tool name via mcp_prefixed_tool_name) instead of a nonexistent <server>_read_resource the agent could hallucinate-call. - The isError path now surfaces EmbeddedResource .resource.text blocks instead of dropping them, so error payloads carried in resources no longer collapse to a bare 'MCP tool returned an error'. (Same-class fix flagged in #64061 and independently addressed in #63576 by @alauer.) - 3 new error-path tests + updated ResourceLink wire-name assertion.
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This was referenced Jul 14, 2026
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Summary
MCP tool results carrying
ResourceLink,EmbeddedResource, orAudioContentblocks are now materialized instead of silently dropped — a PDF-returning MCP tool no longer appears to return metadata only.Salvage of #64061 by @victor-kyriazakos (cherry-picked onto current main, authorship preserved), plus two follow-up fixes on top.
Changes
Cherry-picked from #64061 (@victor-kyriazakos):
tools/mcp_tool.py: new_render_mcp_resource_block()— embedded blob resources are decoded (50 MB cap, enforced on b64 length before decode) and written to the document cache via existingcache_document_from_bytes(); text resources inline;ResourceLinkblocks keep URI/name/MIME with a pointer to the server's read_resource tool (no network fetch);AudioContentcached viacache_audio_from_bytes()as aMEDIA:tag; unrecognized shapes logged instead of dropped.read_resourcehandler: blob contents materialized instead of"[binary data, N bytes]".Follow-ups (ours):
mcp__<server>__read_resource(viamcp_prefixed_tool_name()) instead of a nonexistent<server>_read_resourcethe agent could hallucinate-call.isErrorpath now surfacesEmbeddedResourcetext instead of dropping it — error payloads carried in resources no longer collapse to a bare "MCP tool returned an error". (Same-class gap flagged in fix(mcp): materialize ResourceLink/EmbeddedResource/Audio blocks instead of dropping them #64061's follow-ups and independently fixed in fix(mcp): handle EmbeddedResource tool results #63576 by @alauer — credited.)Validation
tests/tools -k mcp(full MCP suite)mcp__slack__read_resourcenameDuplicate cluster
Same underlying bug reported/fixed in #29962 (@haha0815, earliest), #31356 (@Tranquil-Flow), #38463 (@janrenz), #50999 (@kingofkillers91), #63576 (@alauer). This PR is the most complete implementation — the only one that materializes binary payloads and covers ResourceLink + Audio with size caps and hostile-input tests. The others will be closed with credit.
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