fix(telemetry): correct service.name label and make alerting boot without env

- MetricsRegistry: service.name was recorded as boolean true because the
  string literal "xrpld" bound to the OTel AttributeValue variant's
  char-const* -> bool overload. Assign std::string so it selects the
  string alternative; Prometheus now shows service_name=xrpld (and
  exported_job round-trips correctly) on every MetricsRegistry series.
- Grafana alerting contact points: the Slack url / email addresses used
  ${ENV_VAR} references that expand to empty when unset, and Grafana's
  provisioning validator (which lacks ${VAR:-default} support) then
  crashes the whole stack on startup. Use non-empty disabled placeholders
  (unroutable webhook host, .invalid email) so the stack boots with zero
  configuration; delivery stays off until a real destination is supplied.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docker/telemetry/grafana/provisioning/alerting/contactpoints.yaml

@@ -7,13 +7,20 @@
 #   xrpld-critical  — Slack + email; receives critical-severity alerts.
 # The severity split is wired in policies.yaml.
 #
-# Secrets and personal addresses are NOT hard-coded. Grafana expands
-# ${ENV_VAR} references in provisioning files at load time, so the real
-# Slack webhook and alert-email addresses come from environment variables
-# supplied via docker/telemetry/.env.alerting (gitignored). See
-# .env.alerting.example for the variable list and the Alerting section of
+# Secrets and personal addresses are NOT hard-coded. To enable delivery,
+# replace the disabled placeholder values below with a real Slack webhook
+# and alert email — e.g. by copying docker/telemetry/.env.alerting.example
+# to .env.alerting (gitignored) and swapping the placeholder lines to
+# ${SLACK_WEBHOOK_URL} / ${ALERT_EMAIL_TO}. See the Alerting section of
 # docs/telemetry-runbook.md for setup.
-# If a variable is unset, that receiver has no live destination.
+#
+# The defaults are deliberately non-empty, invalid-but-valid-shaped
+# placeholders (an unroutable webhook host and a .invalid email). Grafana's
+# alerting provisioning validator REQUIRES a non-empty Slack url and email
+# addresses, and it does NOT support ${VAR:-default} expansion — an unset
+# ${VAR} expands to empty and crashes Grafana on startup. The placeholders
+# keep the whole stack booting with zero configuration; alerts simply route
+# nowhere until a real destination is supplied.
 #
 # Email delivery additionally requires SMTP configured on the Grafana
 # service (GF_SMTP_* in docker-compose.yml).
@@ -28,10 +35,11 @@ contactPoints:
       - uid: xrpld-slack-default
         type: slack
         settings:
-          # Incoming-webhook delivery: the channel is fixed by the webhook, so
-          # `recipient` is only here to satisfy Grafana's Slack validator.
-          url: ${SLACK_WEBHOOK_URL}
-          recipient: ${SLACK_CHANNEL}
+          # Disabled placeholder: an unroutable webhook host. A non-empty url
+          # selects Slack webhook mode (no recipient/token required) and keeps
+          # provisioning valid. Replace with a real ${SLACK_WEBHOOK_URL} to
+          # enable delivery.
+          url: https://hooks.slack.invalid/disabled
           title: "{{ .CommonLabels.alertname }} on {{ .CommonLabels.exported_instance }}"
         disableResolveMessage: false
 
@@ -42,13 +50,16 @@ contactPoints:
       - uid: xrpld-slack-critical
         type: slack
         settings:
-          url: ${SLACK_WEBHOOK_URL}
-          recipient: ${SLACK_CHANNEL}
+          # Disabled placeholder — see xrpld-slack-default above.
+          url: https://hooks.slack.invalid/disabled
           title: "[CRITICAL] {{ .CommonLabels.alertname }} on {{ .CommonLabels.exported_instance }}"
         disableResolveMessage: false
       - uid: xrpld-email-critical
         type: email
         settings:
-          addresses: ${ALERT_EMAIL_TO}
+          # Disabled placeholder: a .invalid address keeps the required
+          # `addresses` field non-empty so provisioning validates. Replace
+          # with a real ${ALERT_EMAIL_TO} (and enable SMTP) to deliver.
+          addresses: alerts-disabled@xrpld.invalid
           singleEmail: true
         disableResolveMessage: false

src/xrpld/telemetry/MetricsRegistry.cpp

@@ -182,7 +182,11 @@ MetricsRegistry::start(std::string const& endpoint, std::string const& instanceI
     // Configure resource attributes so Prometheus exported_instance labels
     // distinguish metrics from different nodes (matches OTelCollector setup).
     resource::ResourceAttributes attrs;
-    attrs[opentelemetry::semconv::service::kServiceName] = "xrpld";
+    // Use std::string, not a string literal: ResourceAttributes stores an
+    // OTel AttributeValue variant whose char-const* overload binds to bool,
+    // so "xrpld" would be recorded as the boolean true. std::string selects
+    // the string alternative and the value round-trips as service.name=xrpld.
+    attrs[opentelemetry::semconv::service::kServiceName] = std::string("xrpld");
     if (!instanceId.empty())
         attrs[opentelemetry::semconv::service::kServiceInstanceId] = instanceId;
     auto resourceAttrs = resource::Resource::Create(attrs);