Fix namespaced models foreign key

[andreaslillebo]

First of all, thank you very much for all the effort you put into this gem. It is amazing. 🚀

What this does

Version 1.8.2 breaks namespaced models with custom foreign keys. Consider the following example:

ActiveRecord::Migration.create_table :support_conversations, force: true do |t|
  t.string :model_id
  t.timestamps
end

ActiveRecord::Migration.create_table :support_messages, force: true do |t|
  t.references :conversation, foreign_key: { to_table: :support_conversations }
  t.string :role
  t.text :content
  t.string :model_id
  t.integer :input_tokens
  t.integer :output_tokens
  t.references :tool_call, foreign_key: { to_table: :support_tool_calls }
  t.timestamps
end

ActiveRecord::Migration.create_table :support_tool_calls, force: true do |t|
  t.references :message, foreign_key: { to_table: :support_messages }
  t.string :tool_call_id
  t.string :name
  t.json :arguments
  t.timestamps
end

module Support
  def self.table_name_prefix
    'support_'
  end

  class Conversation < ActiveRecord::Base
    acts_as_chat message_class: 'Support::Message'
  end

  class Message < ActiveRecord::Base
    acts_as_message chat: :conversation, chat_class: 'Support::Conversation', tool_call_class: 'Support::ToolCall'
  end

  class ToolCall < ActiveRecord::Base
    acts_as_tool_call message_class: 'Support::Message'
  end
end

Support::Conversation.last.messages
=> #<ActiveRecord::StatementInvalid:"PG::UndefinedColumn: ERROR:  column support_messages.support_conversation_id does not exist

It does not work, since the correct foreign key should have been support_messages.conversation_id.

I have added a test showcasing this and implemented a fix.

Since we cannot infer foreign keys automatically when it doesn't match the model-name, we expose options to pass in a foreign key, similarly to associations in Rails:

class Support::Message < ActiveRecord::Base
  acts_as_message chat_class: 'Conversation',
                  chat_foreign_key: 'conversation_id'
end

Generators have also been updated to add foreign keys if needed.

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation
• Performance improvement

Scope check

• I read the Contributing Guide
• This aligns with RubyLLM's focus on LLM communication
• This isn't application-specific logic that belongs in user code
• This benefits most users, not just my specific use case

Quality check

• I ran overcommit --install and all hooks pass
• I tested my changes thoroughly
  • For provider changes: Re-recorded VCR cassettes with bundle exec rake vcr:record[provider_name]
  • All tests pass: bundle exec rspec
• I updated documentation if needed
• I didn't modify auto-generated files manually (models.json, aliases.json)

API changes

• Breaking change
• New public methods/classes
• Changed method signatures
• No API changes

Related issues

Fixes bug introduced in #425