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/mitm/store.rs

@@ -537,6 +537,34 @@ impl MitmStore {
         std::mem::take(&mut *self.tool_rounds.write().await)
     }
 
+    /// Push a new tool round from Google's response (calls only, results empty).
+    /// Called by proxy.rs when the MITM intercepts functionCall parts.
+    pub async fn push_tool_round_calls(&self, calls: Vec<CapturedFunctionCall>) {
+        if !calls.is_empty() {
+            self.tool_rounds.write().await.push(ToolRound {
+                calls,
+                results: Vec::new(),
+            });
+        }
+    }
+
+    /// Attach tool results to the latest incomplete tool round (one with empty results).
+    /// Called by responses.rs/gemini.rs when the client sends tool results.
+    /// If there's no open round, creates a legacy round with no calls.
+    pub async fn attach_tool_round_results(&self, results: Vec<PendingToolResult>) {
+        let mut rounds = self.tool_rounds.write().await;
+        // Find the last round that has no results yet
+        if let Some(round) = rounds.iter_mut().rev().find(|r| r.results.is_empty()) {
+            round.results = results;
+        } else {
+            // No open round — probably a race or legacy path, create standalone
+            rounds.push(ToolRound {
+                calls: Vec::new(),
+                results,
+            });
+        }
+    }
+
     // ── Direct response capture (bypass LS) ──────────────────────────────
 
     /// Set (replace) the captured response text.