AgentSession::addArtifact expects ?array $metadata in the third
argument slot; the MCP tool was passing the optional description
string directly, producing a TypeError whenever a caller supplied a
non-null description. Wrap the description into a metadata array so
the call matches the model signature, and add a feature test that
exercises the MCP handler end-to-end to prevent regression.
Closes tasks.lthn.sh/view.php?id=95
Co-authored-by: Codex <noreply@openai.com>
Co-Authored-By: Virgil <virgil@lethean.io>
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