Metrics server doesn't start in non-docker-init deployments

[JasonVranek]

When running commit-boost pbs outside of cb docker init (e.g., in a Kurtosis devnet via the ethereum-package), the metrics server never starts even when [metrics] is configured in cb-config.toml.

Root cause

MetricsProvider::load_and_run() reads the metrics port exclusively from the CB_METRICS_PORT env var via ModuleMetricsConfig::load_from_env(). This env var is only set by docker_init.rs when generating docker-compose files. In any other deployment model the env var is absent, load_from_env() returns None, and the metrics server is skipped with "No metrics server configured".

The [metrics] block in the config file is parsed into CommitBoostConfig.metrics but never consulted at runtime by the PBS service.

Suggested fix

In load_pbs_config() (crates/common/src/config/pbs.rs), after loading the config, set the env var from the config when it isn't already present:

if std::env::var(METRICS_PORT_ENV).is_err() {
    if let Some(ref metrics) = config.metrics {
        if metrics.enabled {
            std::env::set_var(METRICS_PORT_ENV, metrics.start_port.to_string());
        }
    }
}

This preserves the existing behavior when docker_init sets the env var (env takes precedence) and enables metrics in all other deployment modes.

Reproduction

1. Run CB via Kurtosis with a config containing [metrics] host = "0.0.0.0" port = 9090
2. Exec into the container: kurtosis service exec <enclave> <cb-service> "curl -s http://localhost:9090/metrics"
3. Connection refused. The metrics server never started.