fix(router): release a deployment's cost-map key when it is deleted

The ownership ledger only grew. A deleted deployment kept its claim, so if a
later catalog refresh started publishing a model under that same name, the next
registration would treat the catalog entry as the deployment's own and evict it.

Deleting a deployment now gives the key back, which also stops the ledger
growing for the life of the process.

litellm/router.py

@@ -615,7 +615,8 @@ RETRY_BREADCRUMB_LIMIT: Final = 4
 # Cost-map keys created by _register_deployment_in_model_cost, which shares one flat
 # namespace with the built-in model catalog. Only a key it created may be evicted, or a
 # deployment whose id names a real model would strip that model's pricing and
-# capabilities for every other deployment of it.
+# capabilities for every other deployment of it. delete_deployment gives a key back, so a
+# later catalog refresh that starts serving that name is not treated as a deployment's own.
 _DEPLOYMENT_COST_MAP_KEYS: Final[set[str]] = set()  # mutable-ok: ownership of shared cost-map keys
 
 
@@ -9874,6 +9875,7 @@ class Router:
                 _budget_limiter: Final = self._get_router_deployment_budget_limiter()
                 if _budget_limiter is not None:
                     _budget_limiter.unregister_deployment_budget(model_id=id)
+                _DEPLOYMENT_COST_MAP_KEYS.discard(id)
                 try:
                     self._unregister_pre_routing_strategy_for_deployment(
                         deployment=item if isinstance(item, Deployment) else Deployment(**item)

tests/test_litellm/test_router_model_cost_isolation.py

@@ -315,6 +315,39 @@ def test_should_drop_a_stale_price_even_when_the_deployment_declares_a_provider(
         _restore_model_cost_entries(original)
 
 
+def test_should_give_a_cost_map_key_back_when_the_deployment_is_deleted():
+    """Deleting a deployment releases its claim on the shared cost-map key.
+
+    Held forever, a later catalog refresh that starts publishing a model under that same
+    name would be treated as the deleted deployment's own entry and evicted.
+    """
+    from litellm.router import _DEPLOYMENT_COST_MAP_KEYS
+
+    model_id = "deployment-to-delete"
+    original = {model_id: litellm.model_cost.get(model_id)}
+    router = Router(
+        model_list=[
+            {
+                "model_name": "to-delete",
+                "litellm_params": {"model": "gpt-4o-mini", "mock_response": "ok"},
+                "model_info": {"id": model_id, "input_cost_per_token": 0.005},
+            }
+        ]
+    )
+
+    try:
+        assert model_id in _DEPLOYMENT_COST_MAP_KEYS
+
+        assert router.delete_deployment(id=model_id) is not None
+
+        assert model_id not in _DEPLOYMENT_COST_MAP_KEYS, (
+            "a deleted deployment kept its claim on the shared cost-map key"
+        )
+    finally:
+        _DEPLOYMENT_COST_MAP_KEYS.discard(model_id)
+        _restore_model_cost_entries(original)
+
+
 def test_should_preserve_builtin_pricing_regardless_of_deployment_order():
     """
     The built-in pricing should be preserved no matter which deployment