DEV: Add back validator for Spam setting (#1415)

## 🔍 Overview
This update re-introduces the validator used on the `ai_spam_detection_enabled` setting. It was initially added here: https://github.com/discourse/discourse-ai/pull/1374 to prevent Spam from being enabled without creating an `AiModerationSetting` value in the database. However, due to issues with backups/migrations we temporarily removed it here: https://github.com/discourse/discourse-ai/pull/1393. Now with some internal fixes, we can re-introduce it. We also update the validator so that it only validates when trying to turn on rather than when turning off too.

config/settings.yml

@@ -412,6 +412,7 @@ discourse_ai:
 
   ai_spam_detection_enabled:
     default: false
+    validator: "DiscourseAi::Configuration::SpamDetectionValidator"
   ai_spam_detection_user_id:
     default: ""
     hidden: true

lib/configuration/spam_detection_validator.rb

@@ -8,7 +8,8 @@ module DiscourseAi
       end
 
       def valid_value?(val)
-        return true if Rails.env.test?
+        # only validate when enabling spam detection
+        return true if val == "f" || val == "false"
         return true if AiModerationSetting.spam
 
         false

spec/configuration/llm_enumerator_spec.rb

@@ -62,10 +62,5 @@ RSpec.describe DiscourseAi::Configuration::LlmEnumerator do
         { fake_model.id => [{ type: :automation, name: "some automation", id: automation.id }] },
       )
     end
-
-    it "doesn't error on spam when spam detection is enabled but moderation setting is missing" do
-      SiteSetting.ai_spam_detection_enabled = true
-      expect { described_class.global_usage }.not_to raise_error
-    end
   end
 end

spec/configuration/spam_detection_validator_spec.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+RSpec.describe DiscourseAi::Configuration::SpamDetectionValidator do
+  let(:validator) { described_class.new }
+
+  it "always returns true if setting the value to false" do
+    expect(validator.valid_value?("f")).to eq(true)
+  end
+
+  context "when a moderation setting exists" do
+    fab!(:llm_model)
+    before { AiModerationSetting.create!(setting_type: "spam", llm_model_id: llm_model.id) }
+
+    it "returns true if a moderation setting for spam exists" do
+      expect(validator.valid_value?("t")).to eq(true)
+    end
+  end
+
+  context "when no moderation setting exists" do
+    it "returns false if a moderation setting for spam does not exist" do
+      expect(validator.valid_value?("t")).to eq(false)
+    end
+
+    it "returns an error message when no moderation setting exists" do
+      expect(validator.error_message).to eq(
+        I18n.t("discourse_ai.spam_detection.configuration_missing"),
+      )
+    end
+  end
+end

spec/requests/admin/ai_spam_controller_spec.rb

@@ -209,7 +209,10 @@ RSpec.describe DiscourseAi::Admin::AiSpamController do
 
   describe "#show" do
     context "when logged in as admin" do
-      before { sign_in(admin) }
+      before do
+        sign_in(admin)
+        AiModerationSetting.create!(setting_type: :spam, llm_model_id: llm_model.id)
+      end
 
       it "correctly filters seeded llms" do
         SiteSetting.ai_spam_detection_enabled = true
@@ -248,7 +251,7 @@ RSpec.describe DiscourseAi::Admin::AiSpamController do
       it "return proper settings when spam detection is enabled" do
         SiteSetting.ai_spam_detection_enabled = true
 
-        AiModerationSetting.create(
+        AiModerationSetting.update!(
           {
             setting_type: :spam,
             llm_model_id: llm_model.id,