v2026.7.35

Fixed

• MCP tool calls to stateful (Streamable HTTP) servers now work — invoking a tool on an MCP server that requires a session (e.g. a Brave Search server) failed with Bad Request: Server not initialized — code -32000, even though listing its tools worked. The outbound MCP client was stateless: it never sent initialize, never captured the Mcp-Session-Id response header, and never carried it on the actual call. The client now performs the full Streamable HTTP handshake (initialize → capture session → notifications/initialized → the real call with the session header) for both tool listing and tool calls, and the admin "Test Connection" path uses the same logic. Stateless servers are unaffected — they return no session id, so no session header is added and the call proceeds as before; a server that doesn't support initialize falls back to a direct call. Fixes chat #mention tool calls, the MCP Tool Explorer, and advanced-search MCP sources.