test(providers): isolate the OAuth store in the chatgpt Codex routing test

TestNewRoutesChatGPTCatalogToCodexProvider asserts the chatgpt-account-id header is
empty when no OAuth login is stored, but never redirected the token store — so on a
developer machine with a real chatgpt login it read that login and failed (it still
passed in CI, where no token exists). Point ZERO_OAUTH_TOKENS_PATH at an empty temp
path, mirroring TestNewRoutesChatGPTCatalogWithStoredAccountID, so the test is
deterministic regardless of the developer's stored credentials.

internal/providers/factory_test.go

@@ -264,6 +264,13 @@ func TestNewRejectsUnsupportedProviderKind(t *testing.T) {
 }
 
 func TestNewRoutesChatGPTCatalogToCodexProvider(t *testing.T) {
+	// Isolate the OAuth token store to an empty temp path so the factory reads no
+	// stored login — otherwise this test picks up the developer's real chatgpt
+	// OAuth token and the "want empty chatgpt-account-id" assertion fails locally
+	// (it still passes in CI, where no login is stored). Mirrors the isolation in
+	// TestNewRoutesChatGPTCatalogWithStoredAccountID.
+	t.Setenv("ZERO_OAUTH_TOKENS_PATH", t.TempDir()+"/tokens.json")
+
 	transport := &captureTransport{
 		responseBody: "data: [DONE]\n\n",
 	}