GrpcMetricsInterceptor records into a private SimpleMeterRegistry disconnected from the server registry — gRPC metrics black-holed #4826

Affected version: 26.6.1
Component: GrpcMetricsInterceptor
Severity: MEDIUM (observability)

Summary

The interceptor builds its own new SimpleMeterRegistry() (the comment admits "In
production, integrate with server's meter registry"), disconnected from the global
Metrics registry the rest of the service uses. Per-method metrics are written
into call trailers rather than tagged meters.

Code

GrpcMetricsInterceptor.java:43-58 (private registry), :81-82 (trailers).

Impact

gRPC request/error/duration metrics never reach the real registry — operators see
no gRPC telemetry from this interceptor.

Suggested fix

Inject/look up the server's shared MeterRegistry; record method/status as meter
tags.