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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

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Claude Code v2.1.221

Failure telemetry errorCode is now normalized against a fixed allowlist

Under the hood
Useful1 Signal0
MCP

MCP connection failure reporting now uses a fixed set of error codes instead of raw values.

What

errorCode on tengu_mcp_server_connection_failed is no longer the raw stringified code.

Details
  • It emits missing when absent, keeps numeric codes, keeps values from a fixed list, and otherwise reports other.
  • The list includes new entries such as ERA_NEGOTIATION_FAILED, LIST_PAGINATION_EXCEEDED, METHOD_NOT_SUPPORTED_BY_PROTOCOL_VERSION and the CLIENT_HTTP_* family.
  • The client-side error code map also gained list_pagination_exceeded plus explicit -32000 and -32001 entries.
Evidence

METHOD_NOT_SUPPORTED_BY_PROTOCOL_VERSION

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

See this entry in the whole of v2.1.221 →