test(delivery): deflake TestUnreadableOwedMentionClearedNotReswept — gate on waitForOwed not post-drain owedCount (RIG-2920)

go/internal/delivery/helpers_test.go

@@ -625,8 +625,9 @@ func (f *fakeReads) seedOwedMention(agent store.AccountID, channel store.Channel
 }
 
 // waitForOwed blocks until agent has exactly n owed-mention rows, or fails at the
-// deadline — a polling barrier for the nil-waker case where no dispatch/wake
-// signal is available to gate on (the owed row is the only observable effect).
+// deadline — a polling barrier for cases where the owed-row count is the only
+// observable effect to gate on, e.g. a nil-waker record (no dispatch/wake
+// signal) or a start-edge sweep's ClearOwedMention (owed -> 0 after the sweep).
 func (f *fakeReads) waitForOwed(t *testing.T, agent store.AccountID, n int) {
 	t.Helper()
 	deadline := time.After(testTimeout)

go/internal/delivery/offline_mention_test.go

@@ -233,14 +233,14 @@ func TestUnreadableOwedMentionClearedNotReswept(t *testing.T) {
 	startConsumer(t, c)
 
 	c.OnSessionStarted("sess-recip", recipient)
-	c.waitStartsDrained(t)
-
+	// The sweep's observable effect is the clear (owed -> 0); gate on it. A bare
+	// waitStartsDrained only proves the start edge was DEQUEUED, not that the
+	// sweep's ClearOwedMention ran (introspect_test.go), so asserting owedCount
+	// right after it races the async sweep and flakes red under CI load.
+	reads.waitForOwed(t, recipient, 0)
 	if got := disp.snapshot(); len(got) != 0 {
 		t.Fatalf("dispatches = %d, want 0 (an unreadable owed message is cleared, not dispatched)", len(got))
 	}
-	if n := reads.owedCount(recipient); n != 0 {
-		t.Fatalf("owed rows for recipient = %d, want 0 (the unreadable row must be cleared)", n)
-	}
 
 	// A second start edge finds nothing owed — the row was cleared, so no re-log loop.
 	c.OnSessionStarted("sess-recip", recipient)