diff --git a/evalharness/agent/envs/tau2_official.py b/evalharness/agent/envs/tau2_official.py
index 6b12ddd..bb0d6b5 100644
--- a/evalharness/agent/envs/tau2_official.py
+++ b/evalharness/agent/envs/tau2_official.py
@@ -123,8 +123,17 @@ class Tau2Environment(Environment):
         task = Task.model_validate(task_json if not isinstance(task_json, str)
                                    else json.loads(task_json))
         domain = (sample.metadata or {}).get('domain') or 'airline'
-        res = run_task(domain=domain, task=task, agent='llm_agent',
-                       user='user_simulator', max_steps=max_turns)
+        # the official engine is SYNCHRONOUS and calls our adapter back via a
+        # private event loop in a worker thread; run it off the main loop so it
+        # never blocks the runner's other benches
+        import concurrent.futures
+
+        loop = asyncio.get_running_loop()
+        with concurrent.futures.ThreadPoolExecutor(max_workers=1) as pool:
+            res = await loop.run_in_executor(
+                pool, lambda: run_task(domain=domain, task=task,
+                                       agent='llm_agent', user='user_simulator',
+                                       max_steps=max_turns))
         rewards = {}
         try:
             info = res.reward_info
diff --git a/evalharness/model/adapter.py b/evalharness/model/adapter.py
index b4f8925..9e24153 100644
--- a/evalharness/model/adapter.py
+++ b/evalharness/model/adapter.py
@@ -25,6 +25,10 @@ from .output import ModelOutput, ToolCall, Usage
 
 ADAPTER_REGISTRY = EvalRegistry('model adapter')
 
+_ADAPTER_CACHE = {}   # spec -> shared instance; keeps pool round-robin state
+                       # GLOBAL across benches (else each pool restarts at the
+                       # first backend and starves the rest)
+
 
 def register_adapter(name: str):
     def decorator(cls):
@@ -87,9 +91,13 @@ def resolve_adapter(spec: str, deploy_fn=None) -> ModelAdapter:
         endpoint = deploy_fn(m.group('deployer'), m.group('model'))
         spec = f"openai/{endpoint['api_base']}?{endpoint['model']}"
     parsed = parse_model_spec(spec)
+    if spec in _ADAPTER_CACHE:
+        return _ADAPTER_CACHE[spec]
     cls = ADAPTER_REGISTRY.get(parsed['adapter'])
     key = parsed.get('api_base') and _key_for(parsed['api_base'])
-    return cls(model=parsed['model'], api_base=parsed['api_base'], api_key=key)
+    inst = cls(model=parsed['model'], api_base=parsed['api_base'], api_key=key)
+    _ADAPTER_CACHE[spec] = inst
+    return inst
 
 
 def _key_for(api_base: str) -> str:
@@ -219,6 +227,10 @@ class OpenAICompatible(ModelAdapter):
             args = fn.get('arguments') or '{}'
             try:
                 args_dict = json.loads(args)
+                if isinstance(args_dict, str):  # double-encoded JSON string
+                    args_dict = json.loads(args_dict)
+                if not isinstance(args_dict, dict):
+                    args_dict = {'raw': args_dict}
             except (ValueError, TypeError):
                 args_dict = {}
             calls.append(ToolCall(id=c.get('id', ''), name=fn.get('name', ''),
diff --git a/evalharness/model/runner.py b/evalharness/model/runner.py
index 064b4e7..051f7db 100644
--- a/evalharness/model/runner.py
+++ b/evalharness/model/runner.py
@@ -382,7 +382,16 @@ def _make_adapter(spec: str) -> ModelAdapter:
     - 'openai-pool/<base-url-template>?model' with {port} placeholder:
       e.g. 'openai-pool/http://127.0.0.1:{8123..8130}/v1?Qwen3-8B' -> N ports
     - else resolve_adapter(spec)        single endpoint
+
+    Pooled specs are CACHED per spec: all benches share one pool so the
+    round-robin counter stays global (independent pools would each restart
+    at the first backend and starve the rest).
     """
+    from .adapter import _ADAPTER_CACHE as _CACHE
+
+    cache_key = spec
+    if cache_key in _CACHE:
+        return _CACHE[cache_key]
     opts = {}
     while True:
         for f in ('!nothink', '!textools'):
@@ -417,6 +426,7 @@ def _make_adapter(spec: str) -> ModelAdapter:
             a.extra['no_think'] = True
         if opts.get('!textools'):
             a.extra['tools_mode'] = 'text'
+    _CACHE[cache_key] = adapter
     return adapter