diff --git a/src/agent/agent_loop.rs b/src/agent/agent_loop.rs
index d87e934..a6668e4 100644
--- a/src/agent/agent_loop.rs
+++ b/src/agent/agent_loop.rs
@@ -2453,6 +2453,57 @@ mod tests {
         // Verify no tool messages remain
         assert!(messages.iter().all(|m| m.role != "tool"));
     }
+
+    #[test]
+    fn test_sanitize_strips_tool_calls_when_tool_results_not_immediately_following() {
+        // [assistant(tool_calls=[A]), user, tool(A)]
+        // Tool result exists but is NOT immediately after assistant → strip tool_calls
+        // This is the scenario that triggers DeepSeek 400 "insufficient tool messages
+        // following tool_calls message" — the reverse scan sees tool(A) as resolved,
+        // but the API requires it to be IMMEDIATELY after the assistant.
+        let mut messages = vec![
+            ChatMessage::assistant_with_tool_calls(
+                "calling tool",
+                vec![ToolCall {
+                    id: "call_A".to_string(),
+                    name: "search".to_string(),
+                    arguments: serde_json::json!({}),
+                }],
+            ),
+            ChatMessage::user("interrupting message"),
+            ChatMessage::tool("call_A", "search", "result"),
+        ];
+
+        let removed = crate::bus::message::sanitize_incomplete_tool_call_sequences(&mut messages);
+        // The assistant should be removed (tool_calls stripped via removal)
+        // and the orphaned tool(A) should also be removed
+        assert!(removed >= 2, "should remove both the assistant and orphaned tool message, got {}", removed);
+        assert_eq!(messages.len(), 1, "only the user message should remain");
+        assert_eq!(messages[0].role, "user");
+        assert!(messages.iter().all(|m| m.tool_calls.as_ref().map_or(true, |c| c.is_empty())),
+                "no assistant should have tool_calls remaining");
+    }
+
+    #[test]
+    fn test_sanitize_preserves_tool_calls_when_immediately_followed() {
+        // [assistant(tool_calls=[A]), tool(A), user] — valid, tool result is immediate
+        let mut messages = vec![
+            ChatMessage::assistant_with_tool_calls(
+                "calling tool",
+                vec![ToolCall {
+                    id: "call_A".to_string(),
+                    name: "search".to_string(),
+                    arguments: serde_json::json!({}),
+                }],
+            ),
+            ChatMessage::tool("call_A", "search", "result"),
+            ChatMessage::user("next message after tool result"),
+        ];
+
+        let removed = crate::bus::message::sanitize_incomplete_tool_call_sequences(&mut messages);
+        assert_eq!(removed, 0, "should not remove anything — tool result immediately follows");
+        assert_eq!(messages.len(), 3);
+    }
 }
 
 #[derive(Debug)]
diff --git a/src/bus/message.rs b/src/bus/message.rs
index 08b611c..dbd0b38 100644
--- a/src/bus/message.rs
+++ b/src/bus/message.rs
@@ -316,6 +316,86 @@ pub(crate) fn sanitize_incomplete_tool_call_sequences(messages: &mut Vec<ChatMes
         }
     }
 
+    // Phase 1.5: Forward-order check — verify tool messages IMMEDIATELY follow
+    // the assistant(tool_calls). If any non-tool message appears between the
+    // assistant and its tool results, the API rejects with
+    // "insufficient tool messages following tool_calls message".
+    //
+    // The reverse scan in Phase 1 only checks existence (tool result appears
+    // somewhere after assistant), NOT immediacy. This pass catches cases like:
+    // [assistant(tool_calls=[A]), user, tool(A)]
+    //   ^ Phase 1 sees tool(A) after assistant → "resolved"
+    //   but API requires tool(A) to be IMMEDIATELY after assistant
+    {
+        let mut pending_tool_ids: HashSet<String> = HashSet::new();
+        let mut pending_assistant_idx: Option<usize> = None;
+
+        for (i, m) in messages.iter().enumerate() {
+            // If we have pending tool_ids and encounter a non-tool message,
+            // the assistant's tool results were NOT immediately following.
+            if !pending_tool_ids.is_empty() && m.role != "tool" {
+                if let Some(idx) = pending_assistant_idx {
+                    if !remove_indices.contains(&idx) {
+                        tracing::warn!(
+                            message_index = idx,
+                            interrupted_by_index = i,
+                            interrupted_by_role = %m.role,
+                            pending_tool_call_count = pending_tool_ids.len(),
+                            "Removing assistant with tool_calls — tool results \
+                             not immediately following (interrupted by non-tool message)"
+                        );
+                        // Remove this assistant's tool_call_ids from with_parent
+                        // so Phase 2 cleans up the now-orphaned tool messages
+                        if let Some(calls) = messages[idx].tool_calls.as_ref() {
+                            for tc in calls.iter() {
+                                with_parent.remove(&tc.id);
+                            }
+                        }
+                        remove_indices.push(idx);
+                    }
+                }
+                pending_tool_ids.clear();
+                pending_assistant_idx = None;
+            }
+
+            if m.role == "assistant"
+                && m.tool_calls.as_ref().map_or(false, |calls| !calls.is_empty())
+            {
+                let already_marked = remove_indices.contains(&i);
+                if !already_marked {
+                    pending_tool_ids = m.tool_calls.as_ref().unwrap()
+                        .iter().map(|tc| tc.id.clone()).collect();
+                    pending_assistant_idx = Some(i);
+                }
+            } else if m.role == "tool" {
+                if let Some(ref tc_id) = m.tool_call_id {
+                    pending_tool_ids.remove(tc_id);
+                    if pending_tool_ids.is_empty() {
+                        pending_assistant_idx = None;
+                    }
+                }
+            }
+        }
+
+        // Handle trailing assistant with unresolved immediate tool results
+        if !pending_tool_ids.is_empty() {
+            if let Some(idx) = pending_assistant_idx {
+                if !remove_indices.contains(&idx) {
+                    tracing::warn!(
+                        message_index = idx,
+                        "Removing trailing assistant with incomplete immediate tool results"
+                    );
+                    if let Some(calls) = messages[idx].tool_calls.as_ref() {
+                        for tc in calls.iter() {
+                            with_parent.remove(&tc.id);
+                        }
+                    }
+                    remove_indices.push(idx);
+                }
+            }
+        }
+    }
+
     // Remove in descending index order to avoid shifting
     for &idx in &remove_indices {
         messages.remove(idx);
diff --git a/src/gateway/execution.rs b/src/gateway/execution.rs
index b812470..73bf432 100644
--- a/src/gateway/execution.rs
+++ b/src/gateway/execution.rs
@@ -219,8 +219,6 @@ impl AgentExecutionService {
             }
             let enriched_content =
                 enrich_user_content_with_media_refs(request.content, &media_refs)?;
-                enrich_user_content_with_media_refs(request.content, &media_refs)?;
-                enrich_user_content_with_media_refs(request.content, &media_refs)?;
 
             // 先计算 user_message_count（在添加新消息之前）
             let history_before = session_guard.get_or_create_history(request.chat_id).clone();
diff --git a/src/providers/openai.rs b/src/providers/openai.rs
index 01d62ad..aac4282 100644
--- a/src/providers/openai.rs
+++ b/src/providers/openai.rs
@@ -672,6 +672,82 @@ impl OpenAIProvider {
             }
         }
 
+        // Forward-order check: verify tool messages IMMEDIATELY follow the
+        // assistant(tool_calls). If any non-tool message appears between the
+        // assistant and its tool results, the API rejects with
+        // "insufficient tool messages following tool_calls message".
+        //
+        // The reverse scan above only checks existence (tool result appears
+        // somewhere after assistant), NOT immediacy. This forward pass catches:
+        // [assistant(tool_calls=[A]), user, tool(A)]
+        //   ^ reverse scan sees tool(A) after assistant → "resolved"
+        //   but API requires tool(A) to be IMMEDIATELY after assistant
+        {
+            let mut pending_tool_ids: std::collections::HashSet<&str> = std::collections::HashSet::new();
+            let mut pending_assistant_idx: Option<usize> = None;
+
+            for (i, m) in request.messages.iter().enumerate() {
+                // If we have pending tool_ids and encounter a non-tool message,
+                // the assistant's tool results were NOT immediately following.
+                if !pending_tool_ids.is_empty() && m.role != "tool" {
+                    if let Some(idx) = pending_assistant_idx {
+                        skip_assistant_indices.insert(idx);
+                        tracing::warn!(
+                            message_index = idx,
+                            interrupted_by_index = i,
+                            interrupted_by_role = %m.role,
+                            pending_tool_call_count = pending_tool_ids.len(),
+                            "build_request_body: assistant tool_calls not immediately \
+                             followed by tool results — stripping tool_calls"
+                        );
+                        // Remove this assistant's tool_call_ids from with_parent
+                        // so orphaned tool messages are dropped during serialization
+                        if let Some(calls) = &request.messages[idx].tool_calls {
+                            for tc in calls.iter() {
+                                with_parent.remove(tc.id.as_str());
+                            }
+                        }
+                    }
+                    pending_tool_ids.clear();
+                    pending_assistant_idx = None;
+                }
+
+                if m.role == "assistant" {
+                    if let Some(ref calls) = m.tool_calls {
+                        if !calls.is_empty() && !skip_assistant_indices.contains(&i) {
+                            pending_tool_ids = calls.iter().map(|tc| tc.id.as_str()).collect();
+                            pending_assistant_idx = Some(i);
+                        }
+                    }
+                } else if m.role == "tool" {
+                    if let Some(ref tc_id) = m.tool_call_id {
+                        pending_tool_ids.remove(tc_id.as_str());
+                        if pending_tool_ids.is_empty() {
+                            pending_assistant_idx = None;
+                        }
+                    }
+                }
+            }
+
+            // Handle trailing assistant with unresolved immediate tool results
+            if !pending_tool_ids.is_empty() {
+                if let Some(idx) = pending_assistant_idx {
+                    skip_assistant_indices.insert(idx);
+                    tracing::warn!(
+                        message_index = idx,
+                        pending_tool_call_count = pending_tool_ids.len(),
+                        "build_request_body: trailing assistant tool_calls without \
+                         immediately following tool results — stripping tool_calls"
+                    );
+                    if let Some(calls) = &request.messages[idx].tool_calls {
+                        for tc in calls.iter() {
+                            with_parent.remove(tc.id.as_str());
+                        }
+                    }
+                }
+            }
+        }
+
         // valid_tool_call_parent_ids = with_parent (assistant tool_call_ids
         // whose parent assistant has ALL results after it)
         let valid_tool_call_parent_ids = &with_parent;
@@ -795,6 +871,48 @@ impl OpenAIProvider {
             body["tools"] = json!(tools);
         }
 
+        // Diagnostic: log the final message sequence when tool_calls are involved.
+        // This captures the exact sequence sent to the API, making 400 errors
+        // like "insufficient tool messages following tool_calls message" easy to
+        // diagnose.
+        let has_tool_calls = body["messages"].as_array()
+            .map(|msgs| msgs.iter().any(|m| m.get("tool_calls").is_some()))
+            .unwrap_or(false);
+        if has_tool_calls {
+            let sequence: Vec<String> = body["messages"].as_array()
+                .map(|msgs| msgs.iter().enumerate().map(|(i, m)| {
+                    let role = m.get("role").and_then(|r| r.as_str()).unwrap_or("?");
+                    match role {
+                        "assistant" => {
+                            let tc_count = m.get("tool_calls")
+                                .and_then(|t| t.as_array())
+                                .map(|a| a.len())
+                                .unwrap_or(0);
+                            if tc_count > 0 {
+                                format!("[{}] assistant(tool_calls={})", i, tc_count)
+                            } else {
+                                format!("[{}] assistant", i)
+                            }
+                        }
+                        "tool" => {
+                            let tcid = m.get("tool_call_id")
+                                .and_then(|t| t.as_str())
+                                .unwrap_or("??");
+                            format!("[{}] tool(id={})", i, tcid)
+                        }
+                        _ => format!("[{}] {}", i, role),
+                    }
+                }).collect())
+                .unwrap_or_default();
+            tracing::info!(
+                provider = %self.name,
+                model = %self.model_id,
+                message_count = sequence.len(),
+                sequence = ?sequence,
+                "build_request_body: final message sequence with tool_calls"
+            );
+        }
+
         body
     }
 }
@@ -1496,4 +1614,131 @@ mod tests {
         // custom_param 应该保留
         assert_eq!(body["custom_param"], Value::String("value".to_string()));
     }
+
+    #[test]
+    fn test_build_request_body_strips_tool_calls_when_not_immediately_followed() {
+        // [assistant(tool_calls=[A]), user, tool(A)] → should strip tool_calls
+        // The tool result exists but a user message interrupts between assistant
+        // and tool result. The API would reject this with
+        // "insufficient tool messages following tool_calls message".
+        let provider = OpenAIProvider::new(
+            "test".to_string(),
+            "key".to_string(),
+            "https://example.com/v1".to_string(),
+            HashMap::new(),
+            120,
+            "gpt-test".to_string(),
+            None,
+            None,
+            HashMap::new(),
+        );
+
+        let request = ChatCompletionRequest {
+            messages: vec![
+                Message {
+                    role: "assistant".to_string(),
+                    content: vec![ContentBlock::text("calling tool")],
+                    reasoning_content: None,
+                    tool_call_id: None,
+                    name: None,
+                    tool_calls: Some(vec![ToolCall {
+                        id: "call_A".to_string(),
+                        name: "search".to_string(),
+                        arguments: json!({}),
+                    }]),
+                },
+                Message {
+                    role: "user".to_string(),
+                    content: vec![ContentBlock::text("interrupting message")],
+                    reasoning_content: None,
+                    tool_call_id: None,
+                    name: None,
+                    tool_calls: None,
+                },
+                Message {
+                    role: "tool".to_string(),
+                    content: vec![ContentBlock::text("result")],
+                    reasoning_content: None,
+                    tool_call_id: Some("call_A".to_string()),
+                    name: Some("search".to_string()),
+                    tool_calls: None,
+                },
+            ],
+            temperature: None,
+            max_tokens: None,
+            tools: None,
+        };
+
+        let body = provider.build_request_body(&request);
+        let messages = body["messages"].as_array().unwrap();
+
+        // Assistant should NOT have tool_calls (stripped because not immediately followed)
+        assert!(
+            messages[0].get("tool_calls").is_none(),
+            "tool_calls should be stripped when tool results are not immediately following"
+        );
+        // Tool message should be dropped (orphaned after stripping)
+        assert_eq!(
+            messages.len(),
+            2,
+            "tool message should be dropped as orphaned, got {} messages",
+            messages.len()
+        );
+    }
+
+    #[test]
+    fn test_build_request_body_preserves_tool_calls_when_immediately_followed() {
+        // [assistant(tool_calls=[A]), tool(A)] → should keep tool_calls (valid sequence)
+        let provider = OpenAIProvider::new(
+            "test".to_string(),
+            "key".to_string(),
+            "https://example.com/v1".to_string(),
+            HashMap::new(),
+            120,
+            "gpt-test".to_string(),
+            None,
+            None,
+            HashMap::new(),
+        );
+
+        let request = ChatCompletionRequest {
+            messages: vec![
+                Message {
+                    role: "assistant".to_string(),
+                    content: vec![ContentBlock::text("calling tool")],
+                    reasoning_content: None,
+                    tool_call_id: None,
+                    name: None,
+                    tool_calls: Some(vec![ToolCall {
+                        id: "call_A".to_string(),
+                        name: "search".to_string(),
+                        arguments: json!({}),
+                    }]),
+                },
+                Message {
+                    role: "tool".to_string(),
+                    content: vec![ContentBlock::text("result")],
+                    reasoning_content: None,
+                    tool_call_id: Some("call_A".to_string()),
+                    name: Some("search".to_string()),
+                    tool_calls: None,
+                },
+            ],
+            temperature: None,
+            max_tokens: None,
+            tools: None,
+        };
+
+        let body = provider.build_request_body(&request);
+        let messages = body["messages"].as_array().unwrap();
+
+        // Assistant should keep tool_calls (valid immediate sequence)
+        let tool_calls = messages[0].get("tool_calls")
+            .and_then(|t| t.as_array())
+            .expect("tool_calls should be preserved when immediately followed");
+        assert_eq!(tool_calls.len(), 1);
+        // Tool message should be present
+        assert_eq!(messages.len(), 2);
+        assert_eq!(messages[1]["role"], "tool");
+    }
 }