Fix replay fallback when model mapping is missing

tests/api/test_admin_usage_routes.py

@@ -7,7 +7,11 @@ from typing import Any
 
 import pytest
 
-from src.api.admin.usage.routes import AdminUsageDetailAdapter, AdminUsageRecordsAdapter
+from src.api.admin.usage.routes import (
+    AdminUsageDetailAdapter,
+    AdminUsageRecordsAdapter,
+    _resolve_replay_model_name,
+)
 
 
 class _FakeQuery:
@@ -273,3 +277,42 @@ async def test_admin_usage_detail_defers_large_body_columns_when_bodies_excluded
     assert (
         "ORM Path[Mapper[Usage(usage)] -> Usage.client_response_body_compressed]" in deferred_paths
     )
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    ("same_provider", "same_endpoint"),
+    [
+        (True, False),
+        (False, False),
+    ],
+    ids=["same-provider-cross-endpoint", "cross-provider"],
+)
+async def test_resolve_replay_model_name_falls_back_to_source_model_when_mapping_missing(
+    monkeypatch: pytest.MonkeyPatch,
+    same_provider: bool,
+    same_endpoint: bool,
+) -> None:
+    class _FakeMapper:
+        def __init__(self, db: Any) -> None:
+            self.db = db
+
+        async def get_mapping(self, source_model: str, provider_id: str) -> None:
+            return None
+
+    monkeypatch.setattr("src.services.model.mapper.ModelMapperMiddleware", _FakeMapper)
+
+    resolved_model, mapping_source = await _resolve_replay_model_name(
+        SimpleNamespace(),
+        source_model="gpt-4o-mini",
+        original_target_model="provider-specific-model",
+        target_provider=SimpleNamespace(id="provider-2", name="OpenAI Compatible"),
+        target_endpoint=SimpleNamespace(id="endpoint-2", api_format="openai:responses"),
+        target_api_key=None,
+        same_provider=same_provider,
+        same_endpoint=same_endpoint,
+        force_remap=False,
+    )
+
+    assert resolved_model == "gpt-4o-mini"
+    assert mapping_source == "none"