From 9f4410622fbc235719b1184c1313aa32a87dd43d Mon Sep 17 00:00:00 2001
From: Zhaochen Li <zli@gitlab.com>
Date: Tue, 1 Jul 2025 12:14:37 +1000
Subject: [PATCH] Handle agent config not found gracefully

---
 .../agent_config_validator.rb                 | 23 +++++++++++++++++++
 .../agent_prerequisites_operations/main.rb    | 13 ++++-------
 ee/lib/remote_development/messages.rb         |  3 +++
 3 files changed, 31 insertions(+), 8 deletions(-)
 create mode 100644 ee/lib/remote_development/agent_prerequisites_operations/agent_config_validator.rb

diff --git a/ee/lib/remote_development/agent_prerequisites_operations/agent_config_validator.rb b/ee/lib/remote_development/agent_prerequisites_operations/agent_config_validator.rb
new file mode 100644
index 00000000000000..56d992c16d9481
--- /dev/null
+++ b/ee/lib/remote_development/agent_prerequisites_operations/agent_config_validator.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+module RemoteDevelopment
+  module AgentPrerequisitesOperations
+    class AgentConfigValidator
+      include Messages
+
+      # @param [Hash] context
+      # @return [Hash]
+      def self.build(context)
+        # NOTE: We do not type-check here because we want to use the fast_spec_helper in the specs.
+        #       We trust that we will get the right object type from the API layer above.
+        context => { agent: agent }
+
+        if agent.unversioned_latest_workspaces_agent_config.present?
+          Gitlab::Fp::Result.ok(context)
+        else
+          Gitlab::Fp::Result.err(AgentPrerequisitesAgentConfigNotFound.new('Agent config not found'))
+        end
+      end
+    end
+  end
+end
diff --git a/ee/lib/remote_development/agent_prerequisites_operations/main.rb b/ee/lib/remote_development/agent_prerequisites_operations/main.rb
index d73501b8a9f3e0..81d75eb50856c1 100644
--- a/ee/lib/remote_development/agent_prerequisites_operations/main.rb
+++ b/ee/lib/remote_development/agent_prerequisites_operations/main.rb
@@ -14,6 +14,7 @@ def self.main(context)
 
         result =
           initial_result
+            .and_then(AgentConfigValidator.method(:validate))
             .map(ResponseBuilder.method(:build))
             .map(
               # As the final step, return the response_payload content in a WorkspaceReconcileSuccessful message
@@ -30,14 +31,10 @@ def self.main(context)
             shared_namespace: String
           }
           { status: :success, payload: message.content }
-
-          # NOTE: This ROP chain currently consists of only `map` steps, there are no `and_then` steps. Therefore it
-          #       is not possible for anything other than the AgentPrerequisitesSuccessful message from the last lambda
-          #       step to be returned. If we ever add an `and_then` step, we should uncomment the else case below, and
-          #       add an appropriate spec example named: "when an unmatched error is returned, an exception is raised"
-          #
-          # else
-          #   raise Gitlab::Fp::UnmatchedResultError.new(result: result)
+        in { err: AgentPrerequisitesAgentConfigNotFound => message }
+          generate_error_response_from_message(message: message, reason: :bad_request)
+        else
+          raise Gitlab::Fp::UnmatchedResultError.new(result: result)
         end
       end
     end
diff --git a/ee/lib/remote_development/messages.rb b/ee/lib/remote_development/messages.rb
index e5040511365156..719747941d219e 100644
--- a/ee/lib/remote_development/messages.rb
+++ b/ee/lib/remote_development/messages.rb
@@ -12,6 +12,9 @@ module Messages
     # AgentConfigOperations errors
     AgentConfigUpdateFailed = Class.new(Gitlab::Fp::Message)
 
+    # AgentPrerequisitesOperations errors
+    AgentPrerequisitesAgentConfigNotFound = Class.new(Gitlab::Fp::Message)
+
     # Workspace create errors
     WorkspaceCreateParamsValidationFailed = Class.new(Gitlab::Fp::Message)
     WorkspaceCreateDevfileLoadFailed = Class.new(Gitlab::Fp::Message)
-- 
GitLab