Everything is streaming (#7247)

Co-authored-by: Douwe Osinga <douwe@squareup.com>
Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

crates/goose/tests/agent.rs

@@ -343,7 +343,8 @@ mod tests {
         use goose::conversation::message::{Message, MessageContent};
         use goose::model::ModelConfig;
         use goose::providers::base::{
-            Provider, ProviderDef, ProviderMetadata, ProviderUsage, Usage,
+            stream_from_single_message, MessageStream, Provider, ProviderDef, ProviderMetadata,
+            ProviderUsage, Usage,
         };
         use goose::providers::errors::ProviderError;
         use goose::session::session_manager::SessionType;
@@ -385,13 +386,14 @@ mod tests {
 
         #[async_trait]
         impl Provider for MockToolProvider {
-            async fn complete(
+            async fn stream(
                 &self,
+                _model_config: &ModelConfig,
                 _session_id: &str,
                 _system_prompt: &str,
                 _messages: &[Message],
                 _tools: &[Tool],
-            ) -> Result<(Message, ProviderUsage), ProviderError> {
+            ) -> Result<MessageStream, ProviderError> {
                 let tool_call = CallToolRequestParams {
                     meta: None,
                     task: None,
@@ -405,21 +407,7 @@ mod tests {
                     Usage::new(Some(10), Some(5), Some(15)),
                 );
 
-                Ok((message, usage))
-            }
-
-            async fn complete_with_model(
-                &self,
-                session_id: Option<&str>,
-                _model_config: &ModelConfig,
-                system_prompt: &str,
-                messages: &[Message],
-                tools: &[Tool],
-            ) -> anyhow::Result<(Message, ProviderUsage), ProviderError> {
-                // Test-only: coerce missing session_id to empty so complete() can be reused.
-                let session_id = session_id.unwrap_or("");
-                self.complete(session_id, system_prompt, messages, tools)
-                    .await
+                Ok(stream_from_single_message(message, usage))
             }
 
             fn get_model_config(&self) -> ModelConfig {