readiness: /metrics answers during boot after decdn#2821; check decdn_node_boot_ready #204

What are you trying to do?

Keep the readiness checks honest once the decdn release that carries decdn/decdn#2821 ships.

#2821 binds the node's /metrics listener before the RPC preflight and the boot chain reads, and adds decdn_node_boot_ready (0 until the node runtime ready banner, then 1). Today every path treats "/metrics answers 200" as "boot finished". After #2821 that no longer holds:

• Chart. charts/decdn-node/values.yaml (the probe comment) and README.md § Probes and lifecycle both say /metrics "binds only after startup completes". The startupProbe, readinessProbe and livenessProbe (all httpGet /metrics) then pass during boot:
  • the pod goes Ready while it is still booting;
  • the 5-minute startup budget no longer restarts a stuck boot, so only the node's own boot deadline ends one.
• Role. ansible/roles/decdn_node/tasks/main.yml § Readiness and the role README treat the probe as advisory because the listener binds late. Its warning text says the same. A 200 during boot would pass the deploy without the node ever reaching ready.
• Compose. decdn-compose health reports decdn-node metrics ok on any 200.
• Molecule. ansible/molecule/default/files/decdn-node-stub and the slow-readiness scenario model the late bind, which becomes old-release behaviour.

What would help?

1. Role readiness: wait for decdn_node_boot_ready 1 in the /metrics body, not just a 200. Rewrite the comment and the warning to match. Decide what a release without the gauge does; once the line's floor carries #2821, it can be treated as not ready.
2. decdn-compose health: report boot-ready from the gauge, not from the status code. Add unit tests.
3. Chart: kubelet httpGet cannot read the gauge's value. So say what the probes now prove (the listener is up), point to DecdnNodeBootStuck (feat(monitoring): alert and panel for decdn_node_boot_ready #203) for a stuck boot, and reconsider the startupProbe budget, possibly with an exec probe if the image has a client.
4. Stub and molecule: have the stub serve /metrics early with decdn_node_boot_ready 0, then flip it to 1. Keep slow-readiness covering the slow boot.

Timing: same rollout as #203 and the decdn bump that carries #2821.

Deploy path

Ansible, Compose, Helm chart