Fix Redis Cluster CROSSSLOT error in debounce Lua script

The debounce Lua script uses two keys (winner + last_seen) that need to
land on the same cluster slot. Added a hash tag so Redis routes them
together. Also fixed the multiple-cooldowns test to not depend on
execution order.

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

Author: chrisguidry

src/docket/dependencies/_debounce.py

@@ -113,12 +113,15 @@ async def __aenter__(self) -> Debounce:
 
         scope = self.scope or docket.name
         if self._argument_name is not None:
-            base_key = f"{scope}:debounce:{self._argument_name}:{self._argument_value}"
+            hash_tag = f"{self._argument_name}:{self._argument_value}"
+            base_key = f"{scope}:debounce:{hash_tag}"
         else:
-            base_key = f"{scope}:debounce:{execution.function_name}"
+            hash_tag = execution.function_name
+            base_key = f"{scope}:debounce:{hash_tag}"
 
-        winner_key = f"{base_key}:winner"
-        seen_key = f"{base_key}:last_seen"
+        # Use a Redis hash tag {…} so both keys land on the same cluster slot
+        winner_key = f"{base_key}:{{{hash_tag}}}:winner"
+        seen_key = f"{base_key}:{{{hash_tag}}}:last_seen"
 
         settle_ms = int(self.settle.total_seconds() * 1000)
         now_ms = int(time.time() * 1000)

tests/test_cooldown.py

@@ -82,14 +82,15 @@ async def task(
         results.append((customer_id, region))
 
     await docket.add(task)(customer_id=1, region="us")
+    await worker.run_until_finished()
+
     await docket.add(task)(
         customer_id=1, region="eu"
     )  # same customer, different region
     await docket.add(task)(
         customer_id=2, region="us"
     )  # different customer, same region
 
-    worker.concurrency = 10
     await worker.run_until_finished()
 
     # First call runs. Second is blocked by customer_id=1. Third is blocked by region="us".