fix(sandbox): avoid blocking sandbox readiness polling (#2822)

* fix(sandbox): offload async sandbox acquisition

Run blocking sandbox provider acquisition through the async provider hook so eager sandbox setup does not stall the event loop.

* fix(sandbox): add async readiness polling

Introduce an async sandbox readiness poller using httpx and asyncio.sleep while preserving the existing synchronous API.

* test(sandbox): cover async readiness polling

Lock in non-blocking readiness behavior so the async helper does not regress to requests.get or time.sleep.

* fix(sandbox): allow anonymous backend creation

* fix(sandbox): use async readiness in provider acquisition

* fix(sandbox): use async acquisition for lazy tools

* test(sandbox): cover anonymous remote creation

* fix(sandbox): clamp async readiness timeout budget

* fix(sandbox): offload async lock file handling

* fix(sandbox): delegate async middleware fallthrough

* docs(sandbox): document async acquisition path

* fix(sandbox): offload async sandbox release

* docs(sandbox): mention async release hook

* fix(sandbox): address async lock review

Reduce duplicate sync/async sandbox acquisition state handling and move async thread-lock waits onto a dedicated executor with cancellation-safe cleanup.

* chore: retrigger ci

Retrigger GitHub Actions after upstream main fixed the stale PR merge lint failure.

* test(sandbox): sync backend unit fixtures

---------

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/packages/harness/deerflow/community/aio_sandbox/remote_backend.py

@@ -59,7 +59,7 @@ class RemoteSandboxBackend(SandboxBackend):
 
     def create(
         self,
-        thread_id: str,
+        thread_id: str | None,
         sandbox_id: str,
         extra_mounts: list[tuple[str, str, bool]] | None = None,
     ) -> SandboxInfo:
@@ -132,7 +132,7 @@ class RemoteSandboxBackend(SandboxBackend):
             logger.warning("Provisioner list_running failed: %s", exc)
             return []
 
-    def _provisioner_create(self, thread_id: str, sandbox_id: str, extra_mounts: list[tuple[str, str, bool]] | None = None) -> SandboxInfo:
+    def _provisioner_create(self, thread_id: str | None, sandbox_id: str, extra_mounts: list[tuple[str, str, bool]] | None = None) -> SandboxInfo:
         """POST /api/sandboxes → create Pod + Service."""
         try:
             resp = requests.post(