insight-chat: code-review polish on the days_radius fix

- Bind effective_radius once in fetch_messages_for_contact so the log
  output and window math share a single source of truth for the clamp.
- Clamp tool-supplied days_radius to [1, 30] at the tool boundary so a
  runaway LLM value can't produce a thousand-day window.
- Split the negative-input test into a real negative-input case
  alongside the zero-input case.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ai/insight_generator.rs

@@ -1812,7 +1812,8 @@ Return ONLY the summary, nothing else."#,
         let days_radius = args
             .get("days_radius")
             .and_then(|v| v.as_i64())
-            .unwrap_or(4);
+            .unwrap_or(4)
+            .clamp(1, 30);
         let limit = args
             .get("limit")
             .and_then(|v| v.as_i64())

src/ai/sms_client.rs

@@ -38,6 +38,7 @@ impl SmsApiClient {
         center_timestamp: i64,
         radius_days: i64,
     ) -> Result<Vec<SmsMessage>> {
+        let effective_radius = radius_days.max(1);
         let (start_ts, end_ts) = Self::window_for_radius(center_timestamp, radius_days);
 
         let center_dt = chrono::DateTime::from_timestamp(center_timestamp, 0)
@@ -48,7 +49,7 @@ impl SmsApiClient {
             log::info!(
                 "Fetching SMS for contact: {} (±{} days from {})",
                 contact_name,
-                radius_days.max(1),
+                effective_radius,
                 center_dt.format("%Y-%m-%d %H:%M:%S")
             );
             let messages = self
@@ -73,7 +74,7 @@ impl SmsApiClient {
         // Fallback to all contacts
         log::info!(
             "Fetching all SMS messages (±{} days from {})",
-            radius_days.max(1),
+            effective_radius,
             center_dt.format("%Y-%m-%d %H:%M:%S")
         );
         self.fetch_messages(start_ts, end_ts, None, Some(center_timestamp))
@@ -399,8 +400,14 @@ mod tests {
     }
 
     #[test]
-    fn window_for_radius_clamps_negative_to_one() {
+    fn window_for_radius_clamps_zero_to_one() {
         let (start, end) = SmsApiClient::window_for_radius(100_000, 0);
         assert_eq!(end - start, 2 * 86400);
     }
+
+    #[test]
+    fn window_for_radius_clamps_negative_to_one() {
+        let (start, end) = SmsApiClient::window_for_radius(100_000, -7);
+        assert_eq!(end - start, 2 * 86400);
+    }
 }