Local /v1/messages: invert disable_parallel_tool_use into parallel_tool_calls (PR #5711)

Anthropic Messages API nests `disable_parallel_tool_use` inside the
`tool_choice` object (per docs.claude.com/parallel-tool-use). The local
Anthropic-compat endpoint dropped that flag because the OpenAI shape it
translates into uses a different name and lives at the top level
instead. SDK clients (anthropic-python, anthropic-sdk-go, etc.) that
already speak this dialect therefore could not opt out of parallel
tool calls against the local GGUF model.

Extract `disable_parallel_tool_use` from the incoming tool_choice and
invert it to `parallel_tool_calls` on the agentic-loop call. Plain-chat
and existing tool_choice shapes are untouched. Added a focused unit
test that pins the dict/None/bool/string boundary cases.

studio/backend/routes/inference.py

@@ -4461,6 +4461,16 @@ async def anthropic_messages(
     if openai_tool_choice is None:
         openai_tool_choice = "auto"
 
+    # Anthropic nests `disable_parallel_tool_use` inside `tool_choice`
+    # (https://docs.claude.com/en/docs/agents-and-tools/tool-use/implement-tool-use).
+    # Flip it into the OpenAI-shaped `parallel_tool_calls` toggle so the
+    # local GGUF tool loop respects clients that opt out of parallel calls.
+    anthropic_parallel_tool_calls: Optional[bool] = None
+    if isinstance(payload.tool_choice, dict):
+        _disable = payload.tool_choice.get("disable_parallel_tool_use")
+        if isinstance(_disable, bool):
+            anthropic_parallel_tool_calls = not _disable
+
     cancel_event = threading.Event()
 
     # ── Tool routing ──────────────────────────────────────────
@@ -4666,6 +4676,7 @@ async def anthropic_messages(
                 auto_heal_tool_calls = True,
                 tool_call_timeout = 300,
                 session_id = payload.session_id,
+                parallel_tool_calls = anthropic_parallel_tool_calls,
             )
 
         if payload.stream:

studio/backend/tests/test_sampling_params_routing.py

@@ -819,3 +819,28 @@ def test_chat_settings_payload_accepts_new_sampling_keys():
     assert ip.stop == ["END"]
     assert ip.serviceTier == "standard_only"
     assert ip.parallelToolCalls is False
+
+
+# ── Local /v1/messages: disable_parallel_tool_use translation ──────────
+
+
+def test_local_anthropic_disable_parallel_tool_use_translation():
+    """Anthropic nests `disable_parallel_tool_use` under `tool_choice`
+    (per docs.claude.com). The local /v1/messages GGUF tool path must
+    invert it into OpenAI-shaped `parallel_tool_calls` so third-party
+    clients (Claude SDK, LiteLLM in passthrough mode) opt out of
+    parallel calls successfully even on the local model."""
+    # Mirror the extraction logic in routes/inference.py:anthropic_messages.
+    def _extract(tc):
+        if isinstance(tc, dict):
+            v = tc.get("disable_parallel_tool_use")
+            if isinstance(v, bool):
+                return not v
+        return None
+
+    assert _extract({"type": "auto", "disable_parallel_tool_use": True}) is False
+    assert _extract({"type": "any", "disable_parallel_tool_use": False}) is True
+    assert _extract({"type": "auto"}) is None
+    assert _extract(None) is None
+    assert _extract("auto") is None  # string form (non-dict) → no opinion
+    assert _extract({"type": "auto", "disable_parallel_tool_use": "yes"}) is None