fix(gateway/api_server): deduplicate concurrent idempotent requests

gateway/platforms/api_server.py

@@ -469,6 +469,7 @@ class _IdempotencyCache:
     def __init__(self, max_items: int = 1000, ttl_seconds: int = 300):
         from collections import OrderedDict
         self._store = OrderedDict()
+        self._inflight: Dict[tuple[str, str], "asyncio.Task[Any]"] = {}
         self._ttl = ttl_seconds
         self._max = max_items
 
@@ -486,11 +487,27 @@ class _IdempotencyCache:
         item = self._store.get(key)
         if item and item["fp"] == fingerprint:
             return item["resp"]
-        resp = await compute_coro()
-        import time as _t
-        self._store[key] = {"resp": resp, "fp": fingerprint, "ts": _t.time()}
-        self._purge()
-        return resp
+
+        inflight_key = (key, fingerprint)
+        task = self._inflight.get(inflight_key)
+        if task is None:
+            async def _compute_and_store():
+                resp = await compute_coro()
+                import time as _t
+                self._store[key] = {"resp": resp, "fp": fingerprint, "ts": _t.time()}
+                self._purge()
+                return resp
+
+            task = asyncio.create_task(_compute_and_store())
+            self._inflight[inflight_key] = task
+
+            def _clear_inflight(done_task: "asyncio.Task[Any]") -> None:
+                if self._inflight.get(inflight_key) is done_task:
+                    self._inflight.pop(inflight_key, None)
+
+            task.add_done_callback(_clear_inflight)
+
+        return await asyncio.shield(task)
 
 
 _idem_cache = _IdempotencyCache()