fix: reset tool call dedup cache each iteration to prevent loops (#3910)

The seen_tool_signatures HashSet was initialized outside the iteration loop, causing cross-iteration deduplication of legitimate tool calls. This triggered a self-correction spiral where the agent repeatedly attempted skipped calls until hitting max_iterations.

Moving the HashSet inside the loop ensures deduplication only applies within a single iteration, as originally intended.

Fixes #3798

src/agent/loop_.rs

@@ -2421,9 +2421,10 @@ pub(crate) async fn run_tool_call_loop(
     };
 
     let turn_id = Uuid::new_v4().to_string();
-    let mut seen_tool_signatures: HashSet<(String, String)> = HashSet::new();
 
     for iteration in 0..max_iterations {
+        let mut seen_tool_signatures: HashSet<(String, String)> = HashSet::new();
+
         if cancellation_token
             .as_ref()
             .is_some_and(CancellationToken::is_cancelled)