fix(aux): normalize GitHub Copilot provider slugs

Keep auxiliary provider resolution aligned with the switch and persisted main-provider paths when models.dev returns github-copilot slugs.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/agent/test_auxiliary_client.py

@@ -19,6 +19,7 @@ from agent.auxiliary_client import (
     _read_codex_access_token,
     _get_provider_chain,
     _is_payment_error,
+    _normalize_aux_provider,
     _try_payment_fallback,
     _resolve_auto,
 )
@@ -54,6 +55,17 @@ def codex_auth_dir(tmp_path, monkeypatch):
     return codex_dir
 
 
+class TestNormalizeAuxProvider:
+    def test_maps_github_copilot_aliases(self):
+        assert _normalize_aux_provider("github") == "copilot"
+        assert _normalize_aux_provider("github-copilot") == "copilot"
+        assert _normalize_aux_provider("github-models") == "copilot"
+
+    def test_maps_github_copilot_acp_aliases(self):
+        assert _normalize_aux_provider("github-copilot-acp") == "copilot-acp"
+        assert _normalize_aux_provider("copilot-acp-agent") == "copilot-acp"
+
+
 class TestReadCodexAccessToken:
     def test_valid_auth_store(self, tmp_path, monkeypatch):
         hermes_home = tmp_path / "hermes"