fix(providers): fall back to configured models when models endpoint fetch fails (#7530)

Signed-off-by: Pete Gonzalez <4673363+octogonz@users.noreply.github.com>
Signed-off-by: Douwe Osinga <douwe@squareup.com>
Co-authored-by: Pete Gonzalez <octogonz@users.noreply.github.com>
Co-authored-by: Douwe Osinga <douwe@squareup.com>

crates/goose/src/providers/errors.rs

@@ -34,6 +34,9 @@ pub enum ProviderError {
     #[error("Unsupported operation: {0}")]
     NotImplemented(String),
 
+    #[error("Endpoint not found (404): {0}")]
+    EndpointNotFound(String),
+
     #[error("Credits exhausted: {details}")]
     CreditsExhausted {
         details: String,
@@ -53,9 +56,14 @@ impl ProviderError {
             ProviderError::ExecutionError(_) => "execution",
             ProviderError::UsageError(_) => "usage",
             ProviderError::NotImplemented(_) => "not_implemented",
+            ProviderError::EndpointNotFound(_) => "endpoint_not_found",
             ProviderError::CreditsExhausted { .. } => "credits_exhausted",
         }
     }
+
+    pub fn is_endpoint_not_found(&self) -> bool {
+        matches!(self, ProviderError::EndpointNotFound(_))
+    }
 }
 
 fn is_network_error(err: &reqwest::Error) -> bool {