fix(parser): prevent DSML markup leak in DeepSeek V4 streaming tool calls

tests/parser/engine/test_deepseek_v4.py

@@ -165,6 +165,14 @@ def test_string_true_not_json_parsed(self):
         assert result["n"] == "42"
         assert isinstance(result["n"], str)
 
+    def test_partial_closing_tag_not_leaked(self):
+        # Regression test for issue #53227: partial DSML tags leak into arguments
+        raw = (
+            '<｜DSML｜parameter name="location" string="true">Paris</｜DSML｜parameter'
+        )
+        result = json.loads(_dsml_arg_converter(raw, partial=True))
+        assert result == {"location": "Paris"}
+
 
 # ── Bare </think> absorption and duplicate <think> absorption ─────────
 

vllm/parser/deepseek_v4.py

@@ -57,7 +57,7 @@
 )
 _PARTIAL_PARAM_RE = re.compile(
     rf'<{_ESCAPED_DSML}parameter\s+name="([^"]+)"\s+string="(true|false)">'
-    rf"(.*)$",
+    rf"((?:(?!</?{_ESCAPED_DSML}).)*)",
     re.DOTALL,
 )