Fix: Azure AI Search Tool Client Lifetime Management (#6316)

## Why are these changes needed?
This PR fixes a bug where the underlying azure `SearchClient` was being
closed prematurely due to use of `async with client` : inside the tool's
run method. this caused the users to encounter errors "HTTP transport
has already been closed"

## Related issue number

Closes #6308 "

## Checks

- [ ] I've included any doc changes needed for
<https://microsoft.github.io/autogen/>. See
<https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md> to
build and test documentation locally.
- [ ] I've added tests (if relevant) corresponding to the changes
introduced in this PR.
- [X] I've made sure all auto checks have passed.

---------

Co-authored-by: Eric Zhu <[email protected]>

Author: jay-thakur

Diff for: python/packages/autogen-ext/src/autogen_ext/tools/azure/_ai_search.py

@@ -241,6 +241,12 @@ def __init__(
         self._client: Optional[SearchClient] = None
         self._cache: Dict[str, Dict[str, Any]] = {}
 
+    async def close(self) -> None:
+        """Explicitly close the Azure SearchClient if needed (for cleanup in long-running apps/tests)."""
+        if self._client is not None:
+            await self._client.close()
+            self._client = None
+
     def _process_credential(
         self, credential: Union[AzureKeyCredential, TokenCredential, Dict[str, str]]
     ) -> Union[AzureKeyCredential, TokenCredential]:
@@ -362,61 +368,62 @@ async def run(
             client = await self._get_client()
             results: List[SearchResult] = []
 
-            async with client:
-                search_future = client.search(text_query, **search_options)  # type: ignore
-
-                if cancellation_token is not None:
-                    import asyncio
-
-                    # Using explicit type ignores to handle Azure SDK type complexity
-                    async def awaitable_wrapper():  # type: ignore # pyright: ignore[reportUnknownVariableType,reportUnknownLambdaType,reportUnknownMemberType]
-                        return await search_future  # pyright: ignore[reportUnknownVariableType]
-
-                    task = asyncio.create_task(awaitable_wrapper())  # type: ignore # pyright: ignore[reportUnknownVariableType]
-                    cancellation_token.link_future(task)  # pyright: ignore[reportUnknownArgumentType]
-                    search_results = await task  # pyright: ignore[reportUnknownVariableType]
-                else:
-                    search_results = await search_future  # pyright: ignore[reportUnknownVariableType]
-
-                async for doc in search_results:  # type: ignore
-                    search_doc: Any = doc
-                    doc_dict: Dict[str, Any] = {}
-
-                    try:
-                        if hasattr(search_doc, "items") and callable(search_doc.items):
-                            dict_like_doc = cast(Dict[str, Any], search_doc)
-                            for key, value in dict_like_doc.items():
-                                doc_dict[str(key)] = value
-                        else:
-                            for key in [
-                                k
-                                for k in dir(search_doc)
-                                if not k.startswith("_") and not callable(getattr(search_doc, k, None))
-                            ]:
-                                doc_dict[key] = getattr(search_doc, key)
-                    except Exception as e:
-                        logger.warning(f"Error processing search document: {e}")
-                        continue
-
-                    metadata: Dict[str, Any] = {}
-                    content: Dict[str, Any] = {}
-                    for key, value in doc_dict.items():
-                        key_str: str = str(key)
-                        if key_str.startswith("@") or key_str.startswith("_"):
-                            metadata[key_str] = value
-                        else:
-                            content[key_str] = value
-
-                    score: float = 0.0
-                    if "@search.score" in doc_dict:
-                        score = float(doc_dict["@search.score"])
-
-                    result = SearchResult(
-                        score=score,
-                        content=content,
-                        metadata=metadata,
-                    )
-                    results.append(result)
+            # Use the persistent client directly. Do NOT close after each operation.
+            # WARNING: The SearchClient must live as long as the tool/agent is in use.
+            search_future = client.search(text_query, **search_options)  # type: ignore
+
+            if cancellation_token is not None:
+                import asyncio
+
+                # Using explicit type ignores to handle Azure SDK type complexity
+                async def awaitable_wrapper():  # type: ignore # pyright: ignore[reportUnknownVariableType,reportUnknownLambdaType,reportUnknownMemberType]
+                    return await search_future  # pyright: ignore[reportUnknownVariableType]
+
+                task = asyncio.create_task(awaitable_wrapper())  # type: ignore # pyright: ignore[reportUnknownVariableType]
+                cancellation_token.link_future(task)  # pyright: ignore[reportUnknownArgumentType]
+                search_results = await task  # pyright: ignore[reportUnknownVariableType]
+            else:
+                search_results = await search_future  # pyright: ignore[reportUnknownVariableType]
+
+            async for doc in search_results:  # type: ignore
+                search_doc: Any = doc
+                doc_dict: Dict[str, Any] = {}
+
+                try:
+                    if hasattr(search_doc, "items") and callable(search_doc.items):
+                        dict_like_doc = cast(Dict[str, Any], search_doc)
+                        for key, value in dict_like_doc.items():
+                            doc_dict[str(key)] = value
+                    else:
+                        for key in [
+                            k
+                            for k in dir(search_doc)
+                            if not k.startswith("_") and not callable(getattr(search_doc, k, None))
+                        ]:
+                            doc_dict[key] = getattr(search_doc, key)
+                except Exception as e:
+                    logger.warning(f"Error processing search document: {e}")
+                    continue
+
+                metadata: Dict[str, Any] = {}
+                content: Dict[str, Any] = {}
+                for key, value in doc_dict.items():
+                    key_str: str = str(key)
+                    if key_str.startswith("@") or key_str.startswith("_"):
+                        metadata[key_str] = value
+                    else:
+                        content[key_str] = value
+
+                score: float = 0.0
+                if "@search.score" in doc_dict:
+                    score = float(doc_dict["@search.score"])
+
+                result = SearchResult(
+                    score=score,
+                    content=content,
+                    metadata=metadata,
+                )
+                results.append(result)
 
             if self.search_config.enable_caching:
                 cache_key = f"{text_query}_{self.search_config.top}"