fix: improve OpenAI stream handling for anomalous tool-call chunks

- filter id-only orphan tool-call chunks without dropping finish metadata
- reattach pending tool-call ids to subsequent payload chunks that omit ids
- detect snapshot-style tool argument chunks and replace buffered arguments
- add unit tests for OpenAI normalization and tool-call argument replacement
- add OpenAI stream integration fixtures for orphan, mixed-chunk, and snapshot cases

Author: wsp1911

src/crates/ai-adapters/src/client/response_aggregator.rs

@@ -47,6 +47,7 @@ pub(crate) async fn aggregate_stream_response(
                         id,
                         name,
                         arguments,
+                        arguments_is_snapshot,
                     } = tool_call;
 
                     if let Some(tool_call_id) = id {
@@ -85,7 +86,11 @@ pub(crate) async fn aggregate_stream_response(
 
                     if let Some(tool_call_arguments) = arguments {
                         if pending_tool_call.has_pending() {
-                            pending_tool_call.append_arguments(&tool_call_arguments);
+                            if arguments_is_snapshot {
+                                pending_tool_call.replace_arguments(&tool_call_arguments);
+                            } else {
+                                pending_tool_call.append_arguments(&tool_call_arguments);
+                            }
                         }
                     }
                 }

src/crates/ai-adapters/src/stream/stream_handler/gemini.rs

@@ -200,13 +200,15 @@ mod tests {
             id: None,
             name: Some("get_weather".to_string()),
             arguments: Some("{\"city\":".to_string()),
+            arguments_is_snapshot: false,
         };
         state.assign_id(&mut first);
 
         let mut second = UnifiedToolCall {
             id: None,
             name: Some("get_weather".to_string()),
             arguments: Some("\"Paris\"}".to_string()),
+            arguments_is_snapshot: false,
         };
         state.assign_id(&mut second);
 
@@ -225,6 +227,7 @@ mod tests {
             id: None,
             name: Some("get_weather".to_string()),
             arguments: Some("{}".to_string()),
+            arguments_is_snapshot: false,
         };
         state.assign_id(&mut first);
         state.on_non_tool_response();
@@ -233,6 +236,7 @@ mod tests {
             id: None,
             name: Some("get_weather".to_string()),
             arguments: Some("{}".to_string()),
+            arguments_is_snapshot: false,
         };
         state.assign_id(&mut second);
 
@@ -252,11 +256,13 @@ mod tests {
             id: None,
             name: Some("grep".to_string()),
             arguments: Some("{}".to_string()),
+            arguments_is_snapshot: false,
         };
         let mut second = UnifiedToolCall {
             id: None,
             name: Some("read".to_string()),
             arguments: Some("{}".to_string()),
+            arguments_is_snapshot: false,
         };
 
         first_state.assign_id(&mut first);