ReplSession.frameSource(): Promise<{ text: string; line: number; } | null>
The source the breakpoint is in and the line it stopped on, or null when nothing is stopped.
The ORIGINAL source where there is one: a pause inside a preloaded file reports that file and its own line numbers rather than the bundle's. Typed-in functions have no file, and their source comes back from the page, which is the only place it exists.