docs(gw-listener): update metrics docs for wall-clock timeouts, clarify Default is test-only

Author: Eikix

coprocessor/fhevm-engine/gw-listener/src/lib.rs

@@ -78,6 +78,8 @@ pub fn chain_id_from_env() -> Option<ChainId> {
     }
 }
 
+/// Default is used by unit tests only. Production defaults come from
+/// the CLI arg definitions in `bin/gw_listener.rs` (e.g. `--drift-no-consensus-timeout 5m`).
 impl Default for ConfigSettings {
     fn default() -> Self {
         Self {

docs/metrics/metrics.md

@@ -137,11 +137,11 @@ Note that recommendations assume a smoke test that runs transactions/requests at
 
 #### Metric Name: `coprocessor_gw_listener_consensus_latency_blocks`
  - **Type**: Histogram
- - **Description**: Block distance between the first observed submission and the consensus event for a handle. Use this distribution to tune `--drift-no-consensus-timeout-blocks`: the timeout should sit above the normal tail so it alerts on truly stalled handles without retaining healthy ones for too long. Bucket boundaries: 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144.
+ - **Description**: Block distance between the first observed submission and the consensus event for a handle. Diagnostic metric for understanding on-chain latency; timeouts are wall-clock based and configured via `--drift-no-consensus-timeout`. Bucket boundaries: 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144.
 
 #### Metric Name: `coprocessor_gw_listener_post_consensus_completion_blocks`
  - **Type**: Histogram
- - **Description**: Block distance between the consensus event and seeing all expected submissions for a handle. Use this distribution to tune `--drift-post-consensus-grace-blocks`: the grace window should sit above the normal tail so lagging-but-healthy coprocessors do not alert, while truly missing submissions age out. Bucket boundaries: 0, 1, 2, 3, 5, 8, 13, 21, 34.
+ - **Description**: Block distance between the consensus event and seeing all expected submissions for a handle. Diagnostic metric for understanding on-chain completion latency; the grace window is wall-clock based and configured via `--drift-post-consensus-grace`. Bucket boundaries: 0, 1, 2, 3, 5, 8, 13, 21, 34.
 
 ### zkproof-worker