head-lag: parallel commitmentLevel=Processed sub for codex solana

[Flotapponnier]

Summary

• Codex deprecated onUnconfirmedEventsCreated (changelog 2026-04-20) and already hard-closes it for API-key auth (repro: WS close 1006). Replacement is onEventsCreated(commitmentLevel: [Processed]).
• With an API key, Processed is accepted but silent (0 events vs 16 Confirmed on the same conn) — likely plan-gated. JWT path untestable locally (defined.fi bot checkpoint), so this runs the experiment on prod's own auth: subscribe BOTH legacy and Processed for solana, one-shot log First event on subscription tells us which delivers.
• Processed sub termination (complete/error) is non-fatal: logged, legacy flow continues. Legacy termination still forces reconnect (as per head-lag: subscription-death fixes in the RIGHT harness #1019).
• Gauge takes last write, so double delivery is harmless.

Test plan

• go build
• deploy 3 agg services, grep logs for First event on subscription