fix: extend multi-round tool history to responses and gemini endpoints

- proxy.rs: push_tool_round_calls alongside set_last_function_calls
  when Google responds with functionCall — accumulates rounds
- responses.rs: attach_tool_round_results to pair tool results with
  the correct round instead of flat add_tool_result
- gemini.rs: same attach_tool_round_results integration
- store.rs: add push_tool_round_calls and attach_tool_round_results
  methods for cross-request round accumulation
- Legacy add_tool_result kept for backward compat alongside new path

src/api/responses.rs

@@ -242,6 +242,7 @@ pub(crate) async fn handle_responses(
     // Handle tool result submission (function_call_output in input)
     let is_tool_result_turn = !tool_results.is_empty();
     if is_tool_result_turn {
+        let mut pending: Vec<PendingToolResult> = Vec::new();
         for tr in &tool_results {
             // Look up function name from call_id
             let name = state
@@ -254,17 +255,28 @@ pub(crate) async fn handle_responses(
             let result_value = serde_json::from_str::<serde_json::Value>(&tr.output)
                 .unwrap_or_else(|_| serde_json::json!({"result": tr.output}));
 
+            // Also store as pending (legacy compat)
             state
                 .mitm_store
                 .add_tool_result(PendingToolResult {
-                    name,
-                    result: result_value,
+                    name: name.clone(),
+                    result: result_value.clone(),
                 })
                 .await;
+
+            pending.push(PendingToolResult {
+                name,
+                result: result_value,
+            });
         }
+        // Attach results to the latest open ToolRound (pushed by proxy.rs)
+        state
+            .mitm_store
+            .attach_tool_round_results(pending)
+            .await;
         info!(
             count = tool_results.len(),
-            "Stored tool results for MITM injection"
+            "Stored tool results for MITM injection (attached to tool round)"
         );
     }