feat(acp): add model selection support for session/new and session/set_model (#7112)

Signed-off-by: Adrian Cole <adrian@tetrate.io>

crates/goose/src/providers/errors.rs

@@ -2,7 +2,7 @@ use reqwest::StatusCode;
 use std::time::Duration;
 use thiserror::Error;
 
-#[derive(Error, Debug, PartialEq)]
+#[derive(Error, Debug, Clone, PartialEq)]
 pub enum ProviderError {
     #[error("Authentication error: {0}")]
     Authentication(String),

crates/goose/src/providers/openai.rs

@@ -47,6 +47,7 @@ pub const OPEN_AI_KNOWN_MODELS: &[(&str, usize)] = &[
     ("gpt-3.5-turbo", 16_385),
     ("gpt-4-turbo", 128_000),
     ("o4-mini", 128_000),
+    ("gpt-5-nano", 400_000),
     ("gpt-5.1-codex", 400_000),
     ("gpt-5-codex", 400_000),
 ];