[misc] End the access-log lookup when its window ends

The poll interval was not bounded by the window: a page that came back
without the row just before the deadline still slept a full two seconds
before the loop noticed it was out of budget, so the caller waited longer
than the window it asked for to be told nothing arrived.

Cap the wait at whatever is left of the window.

e2e/agentnetwork/custom_pricing_test.go

@@ -174,6 +174,11 @@ func chatOnce(t *testing.T, ctx context.Context, env pricedEnv, model, sessionID
 // to appear before the caller gives up on it.
 const accessLogIngestWindow = 30 * time.Second
 
+// accessLogPollInterval is how long the lookup waits between pages. Ingest is
+// asynchronous, so the row lands somewhere inside the window rather than on
+// any particular poll.
+const accessLogPollInterval = 2 * time.Second
+
 // lookupAccessLogBySession polls the access-log page for the row carrying
 // sessionID and reports whether it arrived within the window. It never fails
 // the test: callers that can recover — by firing a fresh request under a new
@@ -192,10 +197,23 @@ func lookupAccessLogBySession(ctx context.Context, sessionID string, within time
 				}
 			}
 		}
+		// The wait is bounded by the window as well, so the answer arrives when
+		// the caller's budget runs out rather than a poll interval later: a
+		// full interval slept past the deadline reports "no row" up to two
+		// seconds late, which reads as a slower lookup than the one asked for.
+		wait := time.Until(deadline)
+		if wait > accessLogPollInterval {
+			wait = accessLogPollInterval
+		}
+		if wait <= 0 {
+			return api.AgentNetworkAccessLog{}, false
+		}
+		timer := time.NewTimer(wait)
 		select {
 		case <-ctx.Done():
+			timer.Stop()
 			return api.AgentNetworkAccessLog{}, false
-		case <-time.After(2 * time.Second):
+		case <-timer.C:
 		}
 		// Checked after the wait rather than before the request: a poll issued
 		// past the deadline carries no budget and would fail on arrival.