Read-only memory-leak diagnostics. 404s unless memory_debug_token is configured and matches token — inert in normal operation.

Always returns a gc object-type histogram (which TYPE is multiplying). Drive tracemalloc explicitly: trace=start captures a baseline, trace=diff (later) returns the allocation SITES (file:line) that grew since — i.e. where the leak is — and trace=stop ends tracing. Snapshots use depth 1 and the whole collection runs in a worker thread so it never blocks the event loop; tracing is never auto-started or auto-snapshotted.