fix(goose): only send agent-session-id when a session exists (#6657)

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

crates/goose/tests/agent.rs

@@ -378,12 +378,14 @@ mod tests {
 
             async fn complete_with_model(
                 &self,
-                session_id: &str,
+                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
             }

crates/goose/tests/compaction.rs

@@ -94,9 +94,10 @@ impl MockCompactionProvider {
 
 #[async_trait]
 impl Provider for MockCompactionProvider {
-    async fn complete(
+    async fn complete_with_model(
         &self,
-        _session_id: &str,
+        _session_id: Option<&str>,
+        _model_config: &ModelConfig,
         system_prompt: &str,
         messages: &[Message],
         _tools: &[Tool],
@@ -165,30 +166,6 @@ impl Provider for MockCompactionProvider {
         Ok((message, usage))
     }
 
-    async fn complete_with_model(
-        &self,
-        session_id: &str,
-        _model_config: &ModelConfig,
-        system_prompt: &str,
-        messages: &[Message],
-        tools: &[Tool],
-    ) -> Result<(Message, ProviderUsage), ProviderError> {
-        self.complete(session_id, system_prompt, messages, tools)
-            .await
-    }
-
-    async fn complete_fast(
-        &self,
-        session_id: &str,
-        system_prompt: &str,
-        messages: &[Message],
-        tools: &[Tool],
-    ) -> Result<(Message, ProviderUsage), ProviderError> {
-        // Compaction uses complete_fast, so delegate to complete
-        self.complete(session_id, system_prompt, messages, tools)
-            .await
-    }
-
     fn get_model_config(&self) -> ModelConfig {
         ModelConfig::new("mock-model").unwrap()
     }

crates/goose/tests/mcp_integration_test.rs

@@ -59,7 +59,7 @@ impl Provider for MockProvider {
 
     async fn complete_with_model(
         &self,
-        _session_id: &str,
+        _session_id: Option<&str>,
         _model_config: &ModelConfig,
         _system: &str,
         _messages: &[Message],