head-lag: Robinhood Chain + codex solana Processed migration + mobula-only alerts

[Flotapponnier]

Summary

• New chain on bench 001: Robinhood Chain (Arbitrum Orbit, chainId 4663). Pool USDG/WETH 0x69bf..8d9a (~40k swaps/24h). All 3 sources payload-verified live: mobula fast-trade 28 trades/60s (lag 0.4-2s), gecko SwapChannel pool_id 328167634 (lag ~20s), codex onEventsCreated networkId 4663 (lag ~45s).
• Codex solana migrated from deprecated onUnconfirmedEventsCreated to onEventsCreated(commitmentLevel: [Processed]) — deprecated 2026-04-20, API-key path already hard-closed; Processed verified delivering on the JWT path (sgp logs, headlag_proc_0). Experiment scaffolding from head-lag: parallel commitmentLevel=Processed sub for codex solana #1020 removed.
• Alerts scoped to aggregator="mobula" (AggregatorHeadLagStale + AggregatorWSDisconnected): third-party feed outages are visible on the page, not in Slack.
• Spec: robinhood dimension + per_chain_explainer + text updates (63 specs valid). Logo: official CoinGecko asset-platform PNG.

Test plan

• go build, tsc, validate-specs
• deploy 3 agg + Prometheus, verify robinhood series in prom
• check /benchmarks/aggregator-head-lag?chain=robinhood on staging