apollo_dashboard: exclude observers from strk_to_usd_rate_frozen alert

[matanl-starkware]

Problem

strk_to_usd_rate_frozen fires permanently on observer nodes (seen on apollo-sepolia-alpha-0, the one sepolia-alpha node whose validator_id is outside the committee).

Root cause: oracle_rate_frozen_alert hardcodes ObserverApplicability::Applicable for both exchange-rate oracles, but the two oracles are queried on different consensus paths:

• eth_to_strk is queried on the proposal validation path (validate_proposal.rs → get_l1_prices_in_fri_and_wei), so every node — observers included — keeps its gauge moving. Applicable is correct.
• strk_to_usd is queried only on the proposer build path (build_proposal → compute_proposer_fee_proposal → resolve_fee_target), for the SNIP-35 fee proposal. Validation bounds-checks the proposer's fee_proposal_fri against the local median without an oracle read. An observer never proposes, so its snip35_strk_usd_rate gauge is registered at 0 (ExchangeRateOracleClient::new registers metrics unconditionally) and never updated — present-but-flat by construction, so sum(changes(...[1h])) < 1 is permanently true.

Not an outage: on the observer, snip35_strk_usd_success_count and _error_count are both flat 0 (zero attempts), while all validators read the rate normally via round-robin proposership.

Fix

Parameterize oracle_rate_frozen_alert with ObserverApplicability and pass NotApplicable for strk_to_usd (Applicable for eth_to_strk, unchanged behavior). This matches the oracle success/error-count alerts, which already exclude observers. Regenerated dev_grafana_alerts.json; the only expression change is strk_to_usd_rate_frozen gaining the and on() (is_observer == 0) clause.

Verification

• SEED=0 cargo test -p apollo_dashboard — 16 passed (includes the generated-JSON drift test)
• cargo clippy -p apollo_dashboard --all-targets -- -D warnings — clean
• scripts/rust_fmt.sh — clean

🤖 Generated with Claude Code

[cursor]

PR Summary

Low Risk
Alert-definition-only change that reduces noise on observers; validator monitoring for frozen STRK/USD rates is unchanged.

Overview
Stops false-positive strk_to_usd_rate_frozen alerts on observer nodes by scoping that frozen-rate check to non-observers only.

oracle_rate_frozen_alert now takes ObserverApplicability: eth_to_strk stays Applicable (rate updates on validation for all nodes); strk_to_usd uses NotApplicable because SNIP-35 USD rate is only read when building proposals, so observers keep a flat gauge. Regenerated dev_grafana_alerts.json so strk_to_usd_rate_frozen adds and on() (is_observer == 0); inline docs explain the split.

^{Reviewed by Cursor Bugbot for commit 0211d16. Bugbot is set up for automated code reviews on this repo. Configure here.}

[reviewable-StarkWare]

This change is