`serve` samples `uploads()` every 500ms and emits what changed, so an upload
state shorter than that window never reached the log. Nothing surfaced this
while every upload sat on its slot for a 500ms linger, which was exactly one
poll; with the linger gone a peer can queue and be served between two samples,
and "it had to wait" — the one thing the queue exists to record — silently
disappeared.
The pump now keeps whatever it left waiting, and `serve` drains that alongside
the snapshot, so the fact survives regardless of when the next sample lands.
The list is deduplicated per peer and file and capped, so a caller that never
drains cannot grow it without bound.
This is what made cli_e2e::serve_reports_a_queued_upload_once_the_slots_are_full
fail on CI while passing locally: the assertion was real, and it was timing that
decided whether the client could answer it.
Michel de Graaf
db75a8266a