When the primary request panicked, waiters received a nil response
and nil error, which the proxy turned into an empty HTTP 200.
Recover in the deferred release, store an error response for the
waiters, then re-panic so the primary panic semantics are
unchanged. The test gates the panic on the live waiter count, so
every waiter is coalesced before the release.
In RequestCoalescer.Do, the primary path calls fn() before storing the
response, deleting the inflight key and calling wg.Done(). If fn() panics,
all three steps are skipped: the sync.Map entry leaks and every coalesced
waiter remains blocked on wg.Wait() forever (permanent deadlock for that
key). Route release through a defer so waiters are always released and the
entry cleared, even on panic.
Test: TestRequestCoalescer_PanicSafety (a panicking primary must not poison
the key for subsequent calls).
lukaszraczylo
