The upstream admin gateway tolerates only a small concurrent burst; at
concurrency 4 the tail of the per-row getUserById fan-out was truncated
into empty bodies on every list load (deterministic '—'), and the retries
piled into the same throttle window. Measured 0 failures at concurrency 2
(and 1) versus consistent truncations at 4, so pin enrichment to 2.
A large concurrent burst of getUserById calls during the tunnels-list
email enrichment self-inflicts an upstream throttle (truncated/empty
bodies) that even the per-call retry can't fully escape, intermittently
rendering owner_email as '—'. Add mapWithConcurrency and resolve owner
emails at most a few at a time so each lookup stays inside the throttle
allowance; retry + null fallback preserved.
Gerhard Scheikl