Unclear What the extra metadata fields contain and what they're used for is not stated.
What
When Claude Code calls an MCP (Model Context Protocol) tool — a tool provided by an external server rather than built in — it sends along a small metadata payload with the tool-use ID. Now, when an internal condition is met, extra fields are merged into that metadata payload as well. Previously the payload only ever contained the tool-use ID.
Why
This lets Claude Code pass additional context to MCP tool servers in some sessions, though the finding doesn't specify what that extra context contains or affects.
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What the extra metadata fields contain and what they're used for is not stated.