diff --git a/proto/vantage/v1/vantage.proto b/proto/vantage/v1/vantage.proto
index 942d730..f65b425 100644
--- a/proto/vantage/v1/vantage.proto
+++ b/proto/vantage/v1/vantage.proto
@@ -55,6 +55,7 @@ message AgentMessage {
   oneof payload {
     AgentReady    ready  = 3;
     CommandResult result = 4;
+    StepResult step_result = 5;
   }
 }
 
@@ -89,6 +90,7 @@ message ServerCommand {
     DeleteKeyCmd    delete_key    = 3;
     UpdateAgentCmd  update_agent  = 4;
     ApplyUpdatesCmd apply_updates = 5;
+    RunStepCmd      run_step      = 6;
   }
 }
 
@@ -108,3 +110,18 @@ message GenerateKeyCmd {
   string passphrase = 4; // empty = no passphrase
   string comment    = 5; // embedded in public key
 }
+
+message RunStepCmd {
+  string interpreter      = 1; // "bash" | "powershell"
+  string script           = 2;
+  map<string, string> env = 3;
+  int32  timeout_seconds  = 4;
+}
+
+message StepResult {
+  string command_id             = 1;
+  int32  exit_code              = 2;
+  string stdout                 = 3;
+  string stderr                 = 4;
+  map<string, string> output_env = 5;
+}