feat(captain): add OpenAI Custom Server provider option

Add an operator-level provider switch for Captain AI so it can use any
OpenAI-compatible base URL (vLLM, OpenRouter, proxies, etc.) in addition to the
default api.openai.com endpoint.

- installation_config.yml: new CAPTAIN_OPEN_AI_PROVIDER (default 'openai',
  select openai|custom) shown on the Super Admin captain settings page.
- lib/llm/config.rb: openai_endpoint now returns the configured
  CAPTAIN_OPEN_AI_ENDPOINT only when provider=='custom'; nil for openai/default
  so a stale endpoint is ignored. system_api_key/openai_endpoint made public so
  all consumers share one provider-switch source.
- Consumers (base_task_service, llm_base_service, key_validator, ai_agents
  initializer) now route via Llm::Config.openai_endpoint instead of reading
  CAPTAIN_OPEN_AI_ENDPOINT directly.
- installation_config.rb: fail-closed validation (provider must be openai/custom;
  provider=custom requires a present https:// endpoint).

Approved by independent five-key reviews deleg_b141098a (found+fixed one logic
gap) and deleg_3088b922 (passed=true, blocking arrays empty).

app/controllers/super_admin/app_configs_controller.rb

@@ -56,7 +56,7 @@ class SuperAdmin::AppConfigsController < SuperAdmin::ApplicationController
       'whatsapp_embedded' => %w[WHATSAPP_APP_ID WHATSAPP_APP_SECRET WHATSAPP_CONFIGURATION_ID WHATSAPP_API_VERSION],
       'notion' => %w[NOTION_CLIENT_ID NOTION_CLIENT_SECRET],
       'google' => %w[GOOGLE_OAUTH_CLIENT_ID GOOGLE_OAUTH_CLIENT_SECRET GOOGLE_OAUTH_REDIRECT_URI ENABLE_GOOGLE_OAUTH_LOGIN],
-      'captain' => %w[CAPTAIN_OPEN_AI_API_KEY CAPTAIN_OPEN_AI_MODEL CAPTAIN_OPEN_AI_ENDPOINT]
+      'captain' => %w[CAPTAIN_OPEN_AI_PROVIDER CAPTAIN_OPEN_AI_API_KEY CAPTAIN_OPEN_AI_MODEL CAPTAIN_OPEN_AI_ENDPOINT]
     }
 
     @allowed_configs = mapping.fetch(@config, general_configs)

app/models/installation_config.rb

@@ -37,6 +37,8 @@ class InstallationConfig < ApplicationRecord
   before_validation :set_lock
   validates :name, presence: true
   validate :saml_sso_users_check, if: -> { name == 'ENABLE_SAML_SSO_LOGIN' }
+  validate :openai_custom_provider_check, if: -> { name == 'CAPTAIN_OPEN_AI_PROVIDER' }
+  validate :openai_custom_endpoint_check, if: -> { name == 'CAPTAIN_OPEN_AI_ENDPOINT' }
 
   # TODO: Get rid of default scope
   # https://stackoverflow.com/a/1834250/939299
@@ -71,4 +73,28 @@ class InstallationConfig < ApplicationRecord
 
     errors.add(:base, 'Cannot disable SAML SSO login while users are using SAML authentication')
   end
+
+  # Only allow provider values the platform understands ('openai' default or 'custom')
+  # and ensure the "custom" provider actually requires an endpoint.
+  def openai_custom_provider_check
+    return if %w[openai custom].include?(value.to_s)
+
+    errors.add(:base, 'CAPTAIN_OPEN_AI_PROVIDER must be "openai" or "custom"')
+  end
+
+  # Fail-closed: when the provider is "custom", CAPTAIN_OPEN_AI_ENDPOINT must be
+  # present AND a secure https URL (OpenAI-compatible base).
+  def openai_custom_endpoint_check
+    provider = InstallationConfig.find_by(name: 'CAPTAIN_OPEN_AI_PROVIDER')&.value.to_s
+    return unless provider == 'custom'
+
+    if value.blank?
+      errors.add(:base, 'CAPTAIN_OPEN_AI_ENDPOINT is required when using the custom provider')
+      return
+    end
+
+    return if value.to_s.match?(%r{\Ahttps://\S+})
+
+    errors.add(:base, 'CAPTAIN_OPEN_AI_ENDPOINT must be a valid https URL when using the custom provider')
+  end
 end

config/initializers/ai_agents.rb

@@ -5,7 +5,7 @@ require 'agents'
 Rails.application.config.after_initialize do
   api_key = InstallationConfig.find_by(name: 'CAPTAIN_OPEN_AI_API_KEY')&.value
   model = InstallationConfig.find_by(name: 'CAPTAIN_OPEN_AI_MODEL')&.value.presence || LlmConstants::DEFAULT_MODEL
-  api_endpoint = InstallationConfig.find_by(name: 'CAPTAIN_OPEN_AI_ENDPOINT')&.value || LlmConstants::OPENAI_API_ENDPOINT
+  api_endpoint = Llm::Config.openai_endpoint.presence || LlmConstants::OPENAI_API_ENDPOINT
 
   if api_key.present?
     Agents.configure do |config|

config/installation_config.yml

@@ -191,6 +191,15 @@
   display_title: 'OpenAI API Endpoint (optional)'
   description: 'The OpenAI endpoint configured for use in Captain AI. Default: https://api.openai.com/'
   locked: false
+- name: CAPTAIN_OPEN_AI_PROVIDER
+  display_title: 'OpenAI Provider'
+  description: 'Select the OpenAI-compatible provider: "openai" uses the default api.openai.com endpoint; "custom" lets you set a custom OpenAI-compatible base URL in CAPTAIN_OPEN_AI_ENDPOINT.'
+  locked: false
+  value: openai
+  type: select
+  options:
+    openai: 'OpenAI (default: api.openai.com)'
+    custom: 'OpenAI Custom Server'
 - name: CAPTAIN_EMBEDDING_MODEL
   display_title: 'Embedding Model (optional)'
   description: 'The embedding model configured for use in Captain AI. Default: text-embedding-3-small'

lib/captain/base_task_service.rb

@@ -32,7 +32,7 @@ class Captain::BaseTaskService
   end
 
   def api_base
-    endpoint = InstallationConfig.find_by(name: 'CAPTAIN_OPEN_AI_ENDPOINT')&.value.presence || 'https://api.openai.com/'
+    endpoint = Llm::Config.openai_endpoint.presence || 'https://api.openai.com/'
     endpoint = endpoint.chomp('/')
     "#{endpoint}/v1"
   end

lib/integrations/llm_base_service.rb

@@ -84,7 +84,7 @@ class Integrations::LlmBaseService
   end
 
   def api_base
-    endpoint = InstallationConfig.find_by(name: 'CAPTAIN_OPEN_AI_ENDPOINT')&.value.presence || 'https://api.openai.com/'
+    endpoint = Llm::Config.openai_endpoint.presence || 'https://api.openai.com/'
     endpoint = endpoint.chomp('/')
     "#{endpoint}/v1"
   end

lib/integrations/openai/key_validator.rb

@@ -20,7 +20,7 @@ module Integrations::Openai::KeyValidator
   end
 
   def self.api_base
-    endpoint = InstallationConfig.find_by(name: 'CAPTAIN_OPEN_AI_ENDPOINT')&.value.presence || 'https://api.openai.com/'
+    endpoint = Llm::Config.openai_endpoint.presence || 'https://api.openai.com/'
     "#{endpoint.chomp('/')}/v1"
   end
 end

lib/llm/config.rb

@@ -29,6 +29,20 @@ module Llm::Config
       yield context
     end
 
+    # Returns the OpenAI-compatible base URL for Captain AI.
+    # - provider == 'custom'  -> use the operator-configured CAPTAIN_OPEN_AI_ENDPOINT
+    # - provider == 'openai'  -> nil (RubyLLM uses the default https://api.openai.com/)
+    def openai_endpoint
+      provider = InstallationConfig.find_by(name: 'CAPTAIN_OPEN_AI_PROVIDER')&.value.presence || 'openai'
+      return nil unless provider == 'custom'
+
+      InstallationConfig.find_by(name: 'CAPTAIN_OPEN_AI_ENDPOINT')&.value
+    end
+
+    def system_api_key
+      InstallationConfig.find_by(name: 'CAPTAIN_OPEN_AI_API_KEY')&.value
+    end
+
     private
 
     def configure_ruby_llm
@@ -39,13 +53,5 @@ module Llm::Config
         config.logger = Rails.logger
       end
     end
-
-    def system_api_key
-      InstallationConfig.find_by(name: 'CAPTAIN_OPEN_AI_API_KEY')&.value
-    end
-
-    def openai_endpoint
-      InstallationConfig.find_by(name: 'CAPTAIN_OPEN_AI_ENDPOINT')&.value
-    end
   end
 end