fix: reconsolidate split tool-call messages to follow OpenAI format (#7921)

Signed-off-by: Dale Lakes <6843636+spitfire55@users.noreply.github.com>
Signed-off-by: Dale Lakes <dale.lakes55@gmail.com>
Signed-off-by: Clyde <clyde@users.noreply.github.com>
Co-authored-by: Dale Lakes <6843636+spitfire55@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Clyde <clyde@Clydes-Mac-Studio.local>

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

@@ -340,9 +340,117 @@ pub fn format_messages(messages: &[Message], image_format: &ImageFormat) -> Vec<
         messages_spec.extend(output);
     }
 
+    merge_split_tool_call_messages(&mut messages_spec);
     messages_spec
 }
 
+/// The agent splits a single assistant response with N tool_calls into N
+/// interleaved `asst(TC)/tool` pairs, cloning `reasoning_content` onto each.
+/// This function merges them back into one assistant message with all tool_calls,
+/// followed by the tool results — the standard OpenAI format.
+///
+/// Only merges when `reasoning_content` is present and matches, since that is
+/// the only signal that messages were split from the same turn.
+fn merge_split_tool_call_messages(messages: &mut Vec<Value>) {
+    let mut i = 0;
+    while i < messages.len() {
+        let is_assistant_tool_call = messages[i].get("role") == Some(&json!("assistant"))
+            && messages[i]
+                .get("tool_calls")
+                .and_then(|tc| tc.as_array())
+                .is_some_and(|a| !a.is_empty());
+        let base_reasoning = messages[i].get("reasoning_content");
+
+        if !is_assistant_tool_call || base_reasoning.is_none() {
+            i += 1;
+            continue;
+        }
+        let base_reasoning = base_reasoning.unwrap().clone();
+
+        let mut extra_tool_calls: Vec<Value> = Vec::new();
+        let mut collected: Vec<Value> = Vec::new();
+        let mut scan = i + 1;
+
+        loop {
+            if scan >= messages.len() || messages[scan].get("role") != Some(&json!("tool")) {
+                break;
+            }
+
+            // Skip past tool result and any image-only user messages that
+            // format_messages inserts after tool results containing images.
+            let mut peek = scan + 1;
+            while peek < messages.len() && is_image_only_user_message(&messages[peek]) {
+                peek += 1;
+            }
+
+            if peek >= messages.len() {
+                break;
+            }
+            let next = &messages[peek];
+            let has_no_content = next.get("content").is_none_or(|c| {
+                c.is_null()
+                    || c.as_str().is_some_and(|s| s.is_empty())
+                    || c.as_array().is_some_and(|a| a.is_empty())
+            });
+            let is_split = next.get("role") == Some(&json!("assistant"))
+                && next
+                    .get("tool_calls")
+                    .and_then(|tc| tc.as_array())
+                    .is_some_and(|a| !a.is_empty())
+                && has_no_content
+                && next.get("reasoning_content") == Some(&base_reasoning);
+
+            if !is_split {
+                break;
+            }
+
+            collected.extend(messages[scan..peek].iter().cloned());
+            if let Some(tc) = messages[peek]
+                .get("tool_calls")
+                .and_then(|tc| tc.as_array())
+            {
+                extra_tool_calls.extend(tc.iter().cloned());
+            }
+            scan = peek + 1;
+        }
+
+        if extra_tool_calls.is_empty() {
+            i += 1;
+            continue;
+        }
+
+        if let Some(base_tc) = messages[i]
+            .get_mut("tool_calls")
+            .and_then(|tc| tc.as_array_mut())
+        {
+            base_tc.extend(extra_tool_calls);
+        }
+
+        let insert_at = i + 1;
+        messages.drain(insert_at..scan);
+        let num_collected = collected.len();
+        for (j, msg) in collected.into_iter().enumerate() {
+            messages.insert(insert_at + j, msg);
+        }
+
+        i = insert_at + num_collected;
+    }
+}
+
+/// True if `msg` is a synthetic image-only user message (content is exclusively image_url items).
+fn is_image_only_user_message(msg: &Value) -> bool {
+    msg.get("role") == Some(&json!("user"))
+        && msg
+            .get("content")
+            .and_then(|c| c.as_array())
+            .is_some_and(|arr| {
+                !arr.is_empty()
+                    && arr
+                        .iter()
+                        .all(|item| item.get("type") == Some(&json!("image_url")))
+            })
+}
+
 pub fn format_tools(tools: &[Tool]) -> anyhow::Result<Vec<Value>> {
     let mut tool_names = std::collections::HashSet::new();
     let mut result = Vec::new();
@@ -2110,4 +2218,74 @@ data: [DONE]"#;
             "expected an error but stream completed successfully"
         );
     }
+
+    #[test]
+    fn test_merge_split_tool_calls_with_reasoning() {
+        let mut messages = vec![
+            json!({"role": "assistant", "tool_calls": [{"id": "tc1", "type": "function", "function": {"name": "read", "arguments": "{}"}}], "reasoning_content": "thinking..."}),
+            json!({"role": "tool", "tool_call_id": "tc1", "content": "result1"}),
+            json!({"role": "assistant", "tool_calls": [{"id": "tc2", "type": "function", "function": {"name": "write", "arguments": "{}"}}], "reasoning_content": "thinking..."}),
+            json!({"role": "tool", "tool_call_id": "tc2", "content": "result2"}),
+        ];
+        merge_split_tool_call_messages(&mut messages);
+
+        assert_eq!(messages.len(), 3);
+        assert_eq!(messages[0]["tool_calls"].as_array().unwrap().len(), 2);
+        assert_eq!(messages[1]["role"], "tool");
+        assert_eq!(messages[2]["role"], "tool");
+    }
+
+    #[test]
+    fn test_no_merge_without_reasoning() {
+        let mut messages = vec![
+            json!({"role": "assistant", "tool_calls": [{"id": "tc1", "type": "function", "function": {"name": "read", "arguments": "{}"}}]}),
+            json!({"role": "tool", "tool_call_id": "tc1", "content": "result1"}),
+            json!({"role": "assistant", "tool_calls": [{"id": "tc2", "type": "function", "function": {"name": "write", "arguments": "{}"}}]}),
+            json!({"role": "tool", "tool_call_id": "tc2", "content": "result2"}),
+        ];
+        merge_split_tool_call_messages(&mut messages);
+
+        assert_eq!(messages.len(), 4);
+        assert_eq!(messages[0]["tool_calls"].as_array().unwrap().len(), 1);
+        assert_eq!(messages[2]["tool_calls"].as_array().unwrap().len(), 1);
+    }
+
+    #[test]
+    fn test_merge_split_tool_calls_with_image_gap() {
+        let mut messages = vec![
+            json!({"role": "assistant", "tool_calls": [{"id": "tc1", "type": "function", "function": {"name": "screenshot", "arguments": "{}"}}], "reasoning_content": "thinking..."}),
+            json!({"role": "tool", "tool_call_id": "tc1", "content": "This tool result included an image that is uploaded in the next message."}),
+            json!({"role": "user", "content": [{"type": "image_url", "image_url": {"url": "data:image/png;base64,abc"}}]}),
+            json!({"role": "assistant", "tool_calls": [{"id": "tc2", "type": "function", "function": {"name": "click", "arguments": "{}"}}], "reasoning_content": "thinking..."}),
+            json!({"role": "tool", "tool_call_id": "tc2", "content": "clicked"}),
+        ];
+        merge_split_tool_call_messages(&mut messages);
+
+        assert_eq!(messages.len(), 4);
+        assert_eq!(messages[0]["tool_calls"].as_array().unwrap().len(), 2);
+        assert_eq!(messages[0]["role"], "assistant");
+        assert_eq!(messages[1]["role"], "tool");
+        assert_eq!(messages[1]["tool_call_id"], "tc1");
+        assert_eq!(messages[2]["role"], "user");
+        assert_eq!(messages[3]["role"], "tool");
+        assert_eq!(messages[3]["tool_call_id"], "tc2");
+    }
+
+    #[test]
+    fn test_merge_does_not_skip_real_user_message() {
+        let mut messages = vec![
+            json!({"role": "assistant", "tool_calls": [{"id": "tc1", "type": "function", "function": {"name": "read", "arguments": "{}"}}], "reasoning_content": "thinking..."}),
+            json!({"role": "tool", "tool_call_id": "tc1", "content": "result1"}),
+            json!({"role": "user", "content": "what happened?"}),
+            json!({"role": "assistant", "tool_calls": [{"id": "tc2", "type": "function", "function": {"name": "write", "arguments": "{}"}}], "reasoning_content": "thinking..."}),
+            json!({"role": "tool", "tool_call_id": "tc2", "content": "result2"}),
+        ];
+        merge_split_tool_call_messages(&mut messages);
+
+        assert_eq!(messages.len(), 5);
+        assert_eq!(messages[0]["tool_calls"].as_array().unwrap().len(), 1);
+        assert_eq!(messages[2]["role"], "user");
+        assert_eq!(messages[2]["content"], "what happened?");
+        assert_eq!(messages[3]["tool_calls"].as_array().unwrap().len(), 1);
+    }
 }