fix: [cli] Rewind messages past last user text message, ignore user tool result message

[jsibbison-square]

When a user cancelled during a tool request first a tool response was returned (the tool failed as it was interrupted).

The bug in the code was that we removed existing message upto and including the most recent user message. In this case that would be a tool response message that would be removed. This left the messages with a tool but no tool response which is an invalid request to the model.

Fixed by applying the same logic as goose original and rewinding to the most recent user 'text' message. https://github.com/block/goose/blob/main/packages/exchange/src/exchange/exchange.py#L314

[michaelneale]

nice - looks like not a tiny change so hopefully @baxen gets to take a gander

[jsibbison-square]

nice - looks like not a tiny change so hopefully @baxen gets to take a gander

The actual change is just:

    /// Rewind the messages to before the last user message (they have cancelled it).
    pub fn rewind_messages(&mut self) {
        if self.messages.is_empty() {
            return;
        }

        // Remove messages until we find the last user 'Text' message (not a tool response).
        while let Some(message) = self.messages.last() {
            if message.role == Role::User
                && message
                    .content
                    .iter()
                    .any(|c| matches!(c, MessageContent::Text(_)))
            {
                break;
            }
            self.messages.pop();
        }

        // Remove the last user text message we found.
        if !self.messages.is_empty() {
            self.messages.pop();
        }
    }

The rest is all tests and plumbing (agent Trait for an interface) to enable mocking the agent in the test.

[michaelneale]

nice!