fix(core): log at debug instead of error for expected IPC missing client id state (#3636)

Closes #3631

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Bug Fixes**
* Refined error handling and logging behavior in authentication metadata
retrieval to appropriately categorize and report different error
conditions.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: jakedoublev

service/internal/auth/authn.go

@@ -446,8 +446,13 @@ func IPCMetadataClientInterceptor(log *logger.Logger) connect.UnaryInterceptorFu
 			incoming := true
 			clientID, err := ctxAuth.GetClientIDFromContext(ctx, incoming)
 			if err != nil {
-				// metadata will not always be found over IPC - log other errors
-				if !errors.Is(err, ctxAuth.ErrNoMetadataFound) {
+				switch {
+				case errors.Is(err, ctxAuth.ErrNoMetadataFound):
+				case errors.Is(err, ctxAuth.ErrMissingClientID):
+					// IPC calls may not propagate tokens/clients across service boundaries, which is not
+					// necessarily an error case but is useful to know when debugging
+					log.DebugContext(ctx, "IPCMetadataClientInterceptor", slog.Any("error", err))
+				default:
 					log.ErrorContext(ctx, "IPCMetadataClientInterceptor", slog.Any("error", err))
 				}
 			} else {