MCP server names containing '__' break all native MCP tool calls (server not found) #1731

Summary

An MCP server whose name contains a double underscore (e.g. my__server) — a legal name per sanitizeMcpName — becomes completely unusable: every native MCP tool call for that server fails with "server not found".

Mechanism

buildMcpToolName("my__server", "do_thing") → mcp--my__server--do_thing (the sanitizer preserves _, collapses only --). But normalizeMcpToolName (src/utils/mcp-name.ts:55) splits on /__|--/, treating every __ as a separator, so the name parses to serverName: "my", toolName: "server--do_thing". The server lookup (findServerNameBySanitizedName) misses and the call deterministically fails; consecutiveMistakeCount increments each attempt.

Repro

1. Configure an MCP server named my__server (valid — it connects fine, tools are advertised).
2. Have the model call any of its advertised tools.
3. Result: "server not found" every time.

Suggested fix

Prefer the canonical -- separator when present (a raw -- can only be a separator since the sanitizer collapses it, while __ may be part of a legal name): split on -- if the name contains it, else fall back to the legacy __ split. Existing tool-name shapes keep working.