fix: return digest from attestation state save for OCC support

app/controlplane/api/controlplane/v1/.mockery.yml

@@ -0,0 +1,17 @@
+all: false
+formatter: goimports
+include-auto-generated: false
+log-level: info
+recursive: false
+require-template-schema-exists: true
+template: testify
+template-schema: "{{.Template}}.schema.json"
+packages:
+  github.com/chainloop-dev/chainloop/app/controlplane/api/controlplane/v1:
+    config:
+      dir: "{{.InterfaceDir}}/mocks"
+      filename: "{{.InterfaceName}}.go"
+      pkgname: mocks
+      structname: "{{.InterfaceName}}"
+    interfaces:
+      AttestationStateServiceClient:

app/controlplane/api/controlplane/v1/attestation_state.proto

@@ -1,5 +1,5 @@
 //
-// Copyright 2024 The Chainloop Authors.
+// Copyright 2024-2026 The Chainloop Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -53,7 +53,10 @@ message AttestationStateServiceSaveRequest {
   string base_digest = 3;
 }
 
-message AttestationStateServiceSaveResponse {}
+message AttestationStateServiceSaveResponse {
+  // digest of the newly saved attestation state for Optimistic Concurrency Control
+  string digest = 1;
+}
 
 message AttestationStateServiceReadRequest {
   string workflow_run_id = 1 [(buf.validate.field).string = {min_len: 1}];