What
MCP servers are external tools Claude Code connects to. A stdio server is one that Claude Code runs as a local program. When connecting in automatic negotiation mode, Claude Code first sends a probe to work out which protocol version to use. If that probe timed out, and the server then refuses the start-up request (initialize) with error -32022 (UnsupportedProtocolVersion), Claude Code now restarts the server once and skips the probe. This retry is labelled era_locked_after_probe_timeout.
The features Claude Code tells a server it supports, called client capabilities, are now chosen according to the negotiation mode in use.
Why
A server that is slow to answer the version probe no longer fails to connect. It gets one clean second attempt.
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The title mentions a model-level cap on `tool_use` names, but the finding gives no details about it.