APS bids fail to render ("Missing ad markup or URL") — renderer descriptor lost before registration

[aram356]

Summary

APS OpenRTB bids never render. Every APS bid fails with Prebid's Missing ad markup or URL (reason noAd), so the slot is served an empty creative.

Root cause

APS is bid-by-reference: interpretResponse sets the renderer descriptor on the Prebid bid as the custom trustedServerRenderer field, and a bidResponse listener (installApsBidResponseRegistry) registers it into window.tsjs.apsPrebidRenderers keyed by Prebid's generated adId. The GAM Universal Creative later requests that adId and the bridge serves the APS creative.

Prebid normalizes each bid into its own internal object during addBidResponse and drops unknown top-level fields, so the custom trustedServerRenderer field is gone before the bidResponse listener runs. The listener sees renderer === undefined, returns without registering, and the registry stays empty. When the Universal Creative requests the descriptor, the bridge finds nothing and Prebid's default renderer throws Missing ad markup or URL.

Evidence

Observed on a live deployment with a runtime-instrumented registry:

• The custom field is absent as early as the bidAccepted event (the earliest bid event), for every APS bid.
• The renderer registry receives zero writes across a full session (registrationsCount: 0, validated by proxying the registry object).
• The descriptor itself is valid and registers correctly when exercised in isolation — so it is delivered by /auction and set by interpretResponse, then lost in Prebid's pipeline.
• Result: all APS render failures are bidder=aps, reason=noAd.

Impact

APS renderer bids do not render at all. This affects any deployment serving first-class APS OpenRTB bids.

Fix direction

Make registration independent of the custom field surviving Prebid's normalization: also stash the descriptor keyed by requestId (a first-class field Prebid preserves) at interpretResponse time, and fall back to it in the bidResponse listener when the custom field is absent.