feat(annotate): robust OpenAI-compat client for hosted VLMs

Guard against a choice with no message (safety filter or a thinking model
that spends its whole budget before emitting content) so one empty reply
no longer crashes the whole annotation run; treat it as an empty response
and let the existing JSON-retry path handle it.

Add an optional `reasoning_effort` knob on VlmConfig, forwarded to the
server when set, to cap a thinking model's reasoning (needed for Gemini
via its OpenAI-compatible endpoint).

Co-authored-by: Cursor <cursoragent@cursor.com>

src/lerobot/annotations/steerable_pipeline/config.py

@@ -168,6 +168,12 @@ class VlmConfig:
     # Forwarded as extra_body.chat_template_kwargs (e.g. {"enable_thinking": false}).
     chat_template_kwargs: dict[str, Any] | None = None
 
+    # OpenAI-style thinking budget hint ("low"/"medium"/"high"); forwarded to
+    # the server when set. Used to cap a thinking model's reasoning so it
+    # leaves tokens for the actual JSON answer (e.g. Gemini via its
+    # OpenAI-compatible endpoint).
+    reasoning_effort: str | None = None
+
 
 @dataclass
 class ExecutorConfig:

src/lerobot/annotations/steerable_pipeline/vlm_client.py

@@ -285,6 +285,8 @@ def _make_openai_client(config: VlmConfig) -> VlmClient:
             "max_tokens": max_tok,
             "temperature": temp,
         }
+        if config.reasoning_effort:
+            kwargs["reasoning_effort"] = config.reasoning_effort
         extra_body: dict[str, Any] = {}
         if send_mm_kwargs and mm_kwargs:
             extra_body["mm_processor_kwargs"] = {**mm_kwargs, "do_sample_frames": True}
@@ -296,7 +298,13 @@ def _make_openai_client(config: VlmConfig) -> VlmClient:
             chosen = clients[rr_counter["i"] % len(clients)]
             rr_counter["i"] += 1
         response = chosen.chat.completions.create(**kwargs)
-        return response.choices[0].message.content or ""
+        # Some OpenAI-compatible servers (e.g. Gemini) can return a choice
+        # with no message (safety filter, or a "thinking" model that spends
+        # the whole budget before emitting content). Treat that as an empty
+        # reply so the JSON-retry path handles it instead of crashing the run.
+        choice = response.choices[0] if response.choices else None
+        message = choice.message if choice is not None else None
+        return (message.content if message is not None else None) or ""
 
     def _gen(batch: Sequence[Sequence[dict[str, Any]]], max_tok: int, temp: float) -> list[str]:
         if len(batch) <= 1 or config.client_concurrency <= 1: