feat: add synchronous HTTP client (client.py)

Thin httpx-based wrapper around the DataCleaning HTTP API exposing
reset() / step() / state() / health() with typed Pydantic return values.
Supports context manager usage for automatic connection cleanup.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client.py

@@ -0,0 +1,114 @@
+"""
+Synchronous HTTP client for the Data Cleaning OpenEnv environment.
+
+Usage
+-----
+    from client import DataCleaningEnvClient, DataCleaningAction
+
+    client = DataCleaningEnvClient(base_url="http://localhost:8000")
+
+    # Start a new episode (task_id 1/2/3 or omit for round-robin)
+    result = client.reset(task_id=1)
+    print(result.observation.task_description)
+
+    # Take a step
+    action = DataCleaningAction(
+        operation="fill_missing",
+        column="salary",
+        params={"strategy": "median"},
+    )
+    result = client.step(action)
+    print(result.observation.current_score, result.reward, result.done)
+
+    # Inspect state
+    state = client.state()
+    print(state.episode_id, state.errors_remaining)
+"""
+
+from typing import Optional
+import httpx
+from pydantic import BaseModel
+
+from models import DataCleaningAction, DataCleaningObservation, DataCleaningState
+
+
+class StepResult(BaseModel):
+    """Returned by reset() and step()."""
+    observation: DataCleaningObservation
+    reward: float
+    done: bool
+    info: dict = {}
+
+
+class DataCleaningEnvClient:
+    """
+    Thin synchronous wrapper around the DataCleaning HTTP API.
+
+    All methods raise httpx.HTTPStatusError on non-2xx responses.
+    """
+
+    def __init__(self, base_url: str = "http://localhost:8000", timeout: float = 30.0):
+        self.base_url = base_url.rstrip("/")
+        self._client   = httpx.Client(base_url=self.base_url, timeout=timeout)
+
+    # ------------------------------------------------------------------
+    # Core API
+    # ------------------------------------------------------------------
+
+    def reset(self, task_id: Optional[int] = None) -> StepResult:
+        """
+        Start a new episode.
+
+        Parameters
+        ----------
+        task_id : int | None
+            1 = Easy   (fill missing values)
+            2 = Medium (fix formats + duplicates)
+            3 = Hard   (full pipeline)
+            None = round-robin (1 → 2 → 3 → 1 …)
+        """
+        payload = {"task_id": task_id} if task_id is not None else {}
+        resp    = self._client.post("/reset", json=payload)
+        resp.raise_for_status()
+        return StepResult(**resp.json())
+
+    def step(self, action: DataCleaningAction) -> StepResult:
+        """
+        Apply one cleaning operation and return the updated observation.
+
+        Parameters
+        ----------
+        action : DataCleaningAction
+            operation : str   – one of fill_missing / drop_duplicates /
+                                fix_format / replace_value / drop_outliers / fix_dtype
+            column    : str   – target column (optional for drop_duplicates)
+            params    : dict  – operation-specific parameters
+        """
+        resp = self._client.post("/step", json=action.model_dump())
+        resp.raise_for_status()
+        return StepResult(**resp.json())
+
+    def state(self) -> DataCleaningState:
+        """Return current episode metadata without modifying state."""
+        resp = self._client.post("/state")
+        resp.raise_for_status()
+        return DataCleaningState(**resp.json())
+
+    def health(self) -> dict:
+        """Ping the server. Returns {"status": "ok"} if healthy."""
+        resp = self._client.get("/health")
+        resp.raise_for_status()
+        return resp.json()
+
+    # ------------------------------------------------------------------
+    # Context manager support
+    # ------------------------------------------------------------------
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *_):
+        self.close()
+
+    def close(self):
+        self._client.close()