fix(llm): make gpt-5.x usable through ccproxy Codex OAuth (#324)

* fix(llm): make gpt-5.x usable through ccproxy Codex OAuth

Two independent blockers made current OpenAI models fail when routed
through ccproxy's Codex OAuth endpoint:

1. ccproxy's default Codex model mappings rewrite any gpt-*/o1-*/o3-*/
   claude-* model to gpt-5.3-codex before forwarding, silently overriding
   the configured model and failing outright on accounts where
   gpt-5.3-codex is not served ("The 'gpt-5.3-codex' model is not
   supported when using Codex with a ChatGPT account").
   start_ccproxy() now generates a config with empty codex model
   mappings and passes it via 'ccproxy serve --config'.

2. ccproxy forwards the client's own User-Agent upstream and only
   gap-fills its Codex headers, so the backend gates current models on
   the client identity ("The '<model>' model requires a newer version
   of Codex"). get_chat_model() now sends Codex-CLI-shaped
   originator/version/User-Agent headers when the ccproxy Codex adapter
   is detected, overridable via EVOSCIENTIST_CODEX_CLIENT_VERSION.

Verified live: gpt-5.5 and gpt-5.4 complete successfully through
ccproxy Codex OAuth on a ChatGPT Plus account with both fixes; each
fails without them.

* fix(ccproxy): harden Codex client routing

* fix(llm): keep Codex client identity consistent

* docs: clarify Codex version floor

* style: ruff format models.py after merge

---------

Co-authored-by: Xi Zhang <106144707+X-iZhang@users.noreply.github.com>
Co-authored-by: X-iZhang <zacharyzhang2022@gmail.com>

tests/test_ccproxy_manager.py

@@ -17,6 +17,7 @@ from EvoScientist.ccproxy_manager import (
     setup_codex_env,
     start_ccproxy,
     stop_ccproxy,
+    write_ccproxy_config,
 )
 
 # =============================================================================
@@ -168,6 +169,54 @@ class TestStartCcproxy:
         with pytest.raises(FileNotFoundError):
             start_ccproxy(8000)
 
+    @patch("EvoScientist.ccproxy_manager.is_ccproxy_running")
+    @patch("subprocess.Popen")
+    def test_passes_generated_config(self, mock_popen, mock_running, tmp_path):
+        proc = MagicMock()
+        proc.poll.return_value = None
+        mock_popen.return_value = proc
+        mock_running.side_effect = [True]
+
+        with patch("EvoScientist.config.get_config_dir", return_value=tmp_path):
+            start_ccproxy(8000)
+
+        cmd = mock_popen.call_args[0][0]
+        assert "--config" in cmd
+        assert cmd[cmd.index("--config") + 1] == str(tmp_path / "ccproxy.toml")
+
+    @patch("EvoScientist.ccproxy_manager.is_ccproxy_running")
+    @patch("EvoScientist.ccproxy_manager.write_ccproxy_config", side_effect=OSError)
+    @patch("subprocess.Popen")
+    def test_config_write_failure_starts_without_config(
+        self, mock_popen, mock_write, mock_running
+    ):
+        proc = MagicMock()
+        proc.poll.return_value = None
+        mock_popen.return_value = proc
+        mock_running.side_effect = [True]
+
+        start_ccproxy(8000)
+
+        cmd = mock_popen.call_args[0][0]
+        assert "--config" not in cmd
+
+
+# =============================================================================
+# write_ccproxy_config
+# =============================================================================
+
+
+class TestWriteCcproxyConfig:
+    def test_writes_codex_mapping_override(self, tmp_path):
+        config_dir = tmp_path / "missing" / "config"
+        with patch("EvoScientist.config.get_config_dir", return_value=config_dir):
+            path = write_ccproxy_config()
+
+        assert path == str(config_dir / "ccproxy.toml")
+        content = (config_dir / "ccproxy.toml").read_text(encoding="utf-8")
+        assert "[plugins.codex]" in content
+        assert "model_mappings = []" in content
+
 
 # =============================================================================
 # ensure_ccproxy