MCP SEP-986 tool name format specification not followed

[joshwatson]

Describe the bug

When an MCP server is loaded with tool names that include . or /, the cli will respond to any prompt with something like:

✗ Execution failed: CAPIError: 400 tools.134.custom.name: String should match pattern '^[a-zA-Z0-9_-]{1,128}$'

SEP-986 states, however:

Tool names SHOULD be between 1 and 64 characters in length (inclusive).
Tool names are case-sensitive.
Allowed characters: uppercase and lowercase ASCII letters (A-Z, a-z), digits (0-9), underscore (_), dash (-), dot (.), and forward slash (/).
Tool names SHOULD NOT contain spaces, commas, or other special characters.
Tool names SHOULD be unique within their namespace.
Example valid tool names:

• getUser
• user-profile/update
• DATA_EXPORT_v2
• admin.tools.list

The error above incorrectly specifies the allowed characters, as well as the allowed length (128 v 64).

I tested this behavior by replacing all . with - the mcp server, and it works as expected after that.

Affected version

GitHub Copilot CLI 0.0.423

Steps to reproduce the behavior

1. Install an MCP server that has . in tool names (ex. https://github.com/mrphrazer/binary-ninja-headless-mcp)
2. Type any prompt, press enter

Expected behavior

The prompt should be responded to by the model, without an error message

Additional context

No response