Matches ToolResultEvent pattern with typed inputs via discriminated union.
- Export *ToolInput types from tool schemas
- Add *ToolCallEvent interfaces for each built-in tool
- Add isToolCallEventType() guard with overloads for built-ins
Direct narrowing (event.toolName === "bash") doesn't work due to
CustomToolCallEvent.toolName: string overlapping with literals.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>