Fix replay fallback when model mapping is missing

src/api/admin/usage/routes.py

@@ -1946,19 +1946,19 @@ async def _resolve_replay_model_name(
         )
         return mapped_name, "model_mapping"
 
-    if same_provider and same_endpoint:
-        return source_model, "none"
+    if not (same_provider and same_endpoint):
+        logger.debug(
+            "[replay] No explicit model mapping for '{}' on provider '{}' (endpoint={}, api_format={}); "
+            "forwarding original source model",
+            source_model,
+            target_provider.name or str(target_provider.id),
+            str(getattr(target_endpoint, "id", "") or "unknown"),
+            target_api_format or "unknown",
+        )
 
-    provider_name = target_provider.name or str(target_provider.id)
-    endpoint_id = str(getattr(target_endpoint, "id", "") or "unknown")
-    api_format = target_api_format or "unknown"
-    raise HTTPException(
-        status_code=400,
-        detail=(
-            f"Target provider '{provider_name}' does not support model '{source_model}' "
-            f"(endpoint={endpoint_id}, api_format={api_format})"
-        ),
-    )
+    # Keep replay aligned with the normal request path: if no global-model mapping exists,
+    # forward the original source model name and let the target provider validate it.
+    return source_model, "none"
 
 
 def _apply_replay_model_to_body(

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"