[Bugfix] Fix step3p5 parser when using mtp (#33690)

Signed-off-by: mariohong <mariohong128@gmail.com>

vllm/tool_parsers/step3p5_tool_parser.py

@@ -97,11 +97,26 @@ class StreamingXMLToolCallParser:
         """
         # Record delta count before processing
         initial_delta_count = len(self.deltas)
+        entry_call_id = self.current_call_id
+        entry_tool_call_index = self.tool_call_index
 
         self.streaming_buffer += xml_chunk
 
         found_elements = self._process_complete_xml_elements()
 
+        fallback_call_id = None
+        if entry_call_id is not None:
+            if (
+                self.current_call_id == entry_call_id
+                and self.tool_call_index == entry_tool_call_index
+            ):
+                fallback_call_id = entry_call_id
+        elif (
+            self.current_call_id is not None
+            and self.tool_call_index == entry_tool_call_index + 1
+        ):
+            fallback_call_id = self.current_call_id
+
         if found_elements:
             # If complete elements found, check if end events were missed
             # some tags may not have been triggered
@@ -110,7 +125,7 @@ class StreamingXMLToolCallParser:
                 # If this chunk contains </function>
                 # but didn't generate '}', then complete it
                 if (
-                    self.current_call_id is not None
+                    fallback_call_id is not None
                     and self.function_end_token in xml_chunk
                 ):
                     # - Added '}' (non-empty parameter ending)
@@ -121,7 +136,7 @@ class StreamingXMLToolCallParser:
                             and any(
                                 (
                                     tc.function
-                                    and tc.id == self.current_call_id
+                                    and tc.id == fallback_call_id
                                     and isinstance(tc.function.arguments, str)
                                     and (tc.function.arguments in ("}", "{}"))
                                 )
@@ -139,7 +154,7 @@ class StreamingXMLToolCallParser:
                 # If this chunk contains </tool_call>
                 # but didn't generate final empty delta, then complete it
                 if (
-                    self.current_call_id is not None
+                    fallback_call_id is not None
                     and self.tool_call_end_token in xml_chunk
                 ):
                     has_toolcall_close = any(
@@ -150,7 +165,7 @@ class StreamingXMLToolCallParser:
                                     tc.type == "function"
                                     and tc.function
                                     and tc.function.arguments == ""
-                                    and tc.id == self.current_call_id
+                                    and tc.id == fallback_call_id
                                 )
                                 for tc in td.tool_calls
                             )
@@ -186,7 +201,7 @@ class StreamingXMLToolCallParser:
             # Only execute when still on the same call as when entered,
             # to prevent accidentally closing new calls
             # in multi <tool_call> scenarios
-            if self.current_call_id is not None and (
+            if fallback_call_id is not None and (
                 self.function_end_token in xml_chunk
                 or self.tool_call_end_token in xml_chunk
             ):