Constant MAX_MCP_TOOL_PREFIX_BYTES 

pub const MAX_MCP_TOOL_PREFIX_BYTES: usize = 32;

Maximum byte length of a configured McpConfig::tool_prefix.

UTF-8 bytes, not chars – but since ToolPrefix’s charset is ASCII-only, bytes and chars coincide here. Chosen well under rmcp’s 128-byte SHOULD-level tool name limit (joined = prefix + '_' + tool_name), and conservatively under stricter tool-name limits some LLM client APIs have historically enforced (e.g. ^[a-zA-Z0-9_-]{1,64}$), so a prefix accepted here is unlikely to be rejected downstream by the client. See mcp::server::MAX_TOOL_NAME_BYTES for the compile-time proof tying this constant to the longest currently-registered tool name.