fix(google): handle thoughtSignature differently for Gemini 2.5 vs 3 (#6890)

Signed-off-by: rabi <ramishra@redhat.com>

Author: rabi

crates/goose/src/providers/formats/google.rs

@@ -232,6 +232,25 @@ pub fn process_response_part(
     process_response_part_impl(part, last_signature, handling)
 }
 
+/// Gemini 2.x includes thoughtSignature on first chunk as metadata, not actual thinking.
+fn process_response_part_for_model(
+    part: &Value,
+    last_signature: &mut Option<String>,
+    model_version: Option<&str>,
+) -> Option<MessageContent> {
+    let is_gemini_2 = model_version
+        .map(|m| m.starts_with("gemini-2"))
+        .unwrap_or(false);
+
+    let has_signature = part.get(THOUGHT_SIGNATURE_KEY).is_some();
+    let handling = if has_signature && !is_gemini_2 {
+        SignedTextHandling::SignedTextAsThinking
+    } else {
+        SignedTextHandling::SignedTextAsRegularText
+    };
+    process_response_part_impl(part, last_signature, handling)
+}
+
 fn process_response_part_non_streaming(
     part: &Value,
     last_signature: &mut Option<String>,
@@ -461,6 +480,8 @@ where
                 }
             }
 
+            let model_version = chunk.get("modelVersion").and_then(|v| v.as_str());
+
             let parts = chunk
                 .get("candidates")
                 .and_then(|v| v.as_array())
@@ -471,7 +492,7 @@ where
 
             if let Some(parts) = parts {
                 for part in parts {
-                    if let Some(content) = process_response_part(part, &mut last_signature) {
+                    if let Some(content) = process_response_part_for_model(part, &mut last_signature, model_version) {
                         let message = Message::new(
                             Role::Assistant,
                             chrono::Utc::now().timestamp(),
@@ -1072,18 +1093,71 @@ mod tests {
     async fn test_streaming_with_thought_signature() {
         use futures::StreamExt;
 
-        let signed_stream = concat!(
+        let gemini3_stream = concat!(
             r#"data: {"candidates": [{"content": {"role": "model", "#,
-            r#""parts": [{"text": "Begin", "thoughtSignature": "sig123"}]}}]}"#,
+            r#""parts": [{"text": "Begin", "thoughtSignature": "sig123"}]}}], "#,
+            r#""modelVersion": "gemini-3-pro"}"#,
             "\n",
             r#"data: {"candidates": [{"content": {"role": "model", "#,
-            r#""parts": [{"text": " middle"}]}}]}"#,
+            r#""parts": [{"text": " end"}]}}], "modelVersion": "gemini-3-pro"}"#
+        );
+        let lines: Vec<Result<String, anyhow::Error>> =
+            gemini3_stream.lines().map(|l| Ok(l.to_string())).collect();
+        let stream = Box::pin(futures::stream::iter(lines));
+        let mut message_stream = std::pin::pin!(response_to_streaming_message(stream));
+
+        let mut text_parts = Vec::new();
+        let mut thinking_parts = Vec::new();
+
+        while let Some(result) = message_stream.next().await {
+            let (message, _usage) = result.unwrap();
+            if let Some(msg) = message {
+                match msg.content.first() {
+                    Some(MessageContent::Text(text)) => text_parts.push(text.text.clone()),
+                    Some(MessageContent::Thinking(t)) => thinking_parts.push(t.thinking.clone()),
+                    _ => {}
+                }
+            }
+        }
+
+        assert_eq!(thinking_parts, vec!["Begin"]);
+        assert_eq!(text_parts, vec![" end"]);
+
+        let gemini25_stream = concat!(
+            r#"data: {"candidates": [{"content": {"role": "model", "#,
+            r#""parts": [{"text": "Begin", "thoughtSignature": "sig123"}]}}], "#,
+            r#""modelVersion": "gemini-2.5-pro"}"#,
+            "\n",
+            r#"data: {"candidates": [{"content": {"role": "model", "#,
+            r#""parts": [{"text": " end"}]}}], "modelVersion": "gemini-2.5-pro"}"#
+        );
+        let lines: Vec<Result<String, anyhow::Error>> =
+            gemini25_stream.lines().map(|l| Ok(l.to_string())).collect();
+        let stream = Box::pin(futures::stream::iter(lines));
+        let mut message_stream = std::pin::pin!(response_to_streaming_message(stream));
+
+        let mut text_parts = Vec::new();
+
+        while let Some(result) = message_stream.next().await {
+            let (message, _usage) = result.unwrap();
+            if let Some(msg) = message {
+                if let Some(MessageContent::Text(text)) = msg.content.first() {
+                    text_parts.push(text.text.clone());
+                }
+            }
+        }
+
+        assert_eq!(text_parts, vec!["Begin", " end"]);
+
+        let unknown_stream = concat!(
+            r#"data: {"candidates": [{"content": {"role": "model", "#,
+            r#""parts": [{"text": "Begin", "thoughtSignature": "sig123"}]}}]}"#,
             "\n",
             r#"data: {"candidates": [{"content": {"role": "model", "#,
             r#""parts": [{"text": " end"}]}}]}"#
         );
         let lines: Vec<Result<String, anyhow::Error>> =
-            signed_stream.lines().map(|l| Ok(l.to_string())).collect();
+            unknown_stream.lines().map(|l| Ok(l.to_string())).collect();
         let stream = Box::pin(futures::stream::iter(lines));
         let mut message_stream = std::pin::pin!(response_to_streaming_message(stream));
 
@@ -1094,20 +1168,15 @@ mod tests {
             let (message, _usage) = result.unwrap();
             if let Some(msg) = message {
                 match msg.content.first() {
-                    Some(MessageContent::Text(text)) => {
-                        text_parts.push(text.text.clone());
-                    }
-                    Some(MessageContent::Thinking(thinking)) => {
-                        thinking_parts.push(thinking.thinking.clone());
-                        assert_eq!(thinking.signature, "sig123");
-                    }
+                    Some(MessageContent::Text(text)) => text_parts.push(text.text.clone()),
+                    Some(MessageContent::Thinking(t)) => thinking_parts.push(t.thinking.clone()),
                     _ => {}
                 }
             }
         }
 
         assert_eq!(thinking_parts, vec!["Begin"]);
-        assert_eq!(text_parts, vec![" middle", " end"]);
+        assert_eq!(text_parts, vec![" end"]);
     }
 
     #[tokio::test]