[BUG] acts_as_chat doesn't support file attachments in subsequent messages

[jbritten]

Basic checks

• I searched existing issues - this hasn't been reported
• I can reproduce this consistently
• This is a RubyLLM bug, not my application code

What's broken?

When using acts_as_chat with Rails, file attachments via the with: parameter only work when creating new chats, not when adding messages to existing chats.

How to reproduce

# Create a chat
chat_record = Chat.create!(model: 'claude-sonnet-4')

# This works (response correctly describes diagram)
chat_record.ask("What's in this file?", with: "app/assets/images/diagram.png")

# This does not work (response describes diagram, not chart)
chat_record.ask("What's in this file?", with: "app/assets/images/chart.png")

However, the following, using RubyLLM and not acts_as_chat works as expected:

# Create a chat
chat = RubyLLM.chat(model: 'claude-sonnet-4')

# This works (response correctly describes diagram)
chat.ask("What's in this file?", with: "app/assets/images/diagram.png")

# This works (response correctly describes chart)
chat.ask("What's in this file?", with: "app/assets/images/chart.png")

Expected behavior

The expected behavior is:

1. First message with file: File content should be included in the AI request and the response should reference the file content
2. Subsequent messages with different files: Each new file should be processed and included in the AI request, with the response correctly referencing the new file content
3. Consistent behavior: File attachments should work the same way whether it's the first message or the 10th message in a conversation

The Rails integration should behave identically to the raw RubyLLM chat instance, where file attachments work correctly in all subsequent messages. The acts_as_chat helper should not change the core functionality of file attachment processing.

Current behavior: Only the first file attachment in a conversation is processed correctly; subsequent file attachments are ignored.

Expected behavior: All file attachments should be processed correctly, regardless of their position in the conversation history.

What actually happened

• File attachments are ignored in subsequent messages
• Only works with fresh RubyLLM.chat instances
• Breaks the conversation flow for applications that need to add files mid-conversation

Environment

• Ruby version: 3.3.8
• RubyLLM version: 1.8.2
• Rails version: 8.0.2
• Provider: OpenAI
• OS: MacOS 15.6.1

[marmolleonardo]

I have the same issue, to reproduce I used the interface to attachment a file.

[crmne]

I tried with claude-sonnet-4 and gpt-4.1-nano and I can't reproduce. Can you post the contents of your Chat, and Message models? Have you updated to the new acts_as_chat interface? https://rubyllm.com/upgrading-to-1-7/