fix: write refreshed Codex tokens back to ~/.codex/auth.json (#8277)

OpenAI OAuth refresh tokens are single-use and rotate on every refresh.
When Hermes refreshes a Codex token, it consumed the old refresh_token
but never wrote the new pair back to ~/.codex/auth.json. This caused
Codex CLI and VS Code to fail with 'refresh_token_reused' on their
next refresh attempt.

This mirrors the existing Anthropic write-back pattern where refreshed
tokens are written to ~/.claude/.credentials.json via
_write_claude_code_credentials().

Changes:
- Add _write_codex_cli_tokens() in hermes_cli/auth.py (parallel to
  _write_claude_code_credentials in anthropic_adapter.py)
- Call it from _refresh_codex_auth_tokens() (non-pool refresh path)
- Call it from credential_pool._refresh_entry() (pool happy path + retry)
- Add tests for the new write-back behavior
- Update existing test docstring to clarify _save_codex_tokens vs
  _write_codex_cli_tokens separation

Fixes refresh token conflict reported by @ec12edfae2cb221

tests/hermes_cli/test_auth_codex_provider.py

@@ -14,6 +14,7 @@ from hermes_cli.auth import (
     PROVIDER_REGISTRY,
     _read_codex_tokens,
     _save_codex_tokens,
+    _write_codex_cli_tokens,
     _import_codex_cli_tokens,
     get_codex_auth_status,
     get_provider_auth_state,
@@ -161,7 +162,7 @@ def test_import_codex_cli_tokens_missing(tmp_path, monkeypatch):
 
 
 def test_codex_tokens_not_written_to_shared_file(tmp_path, monkeypatch):
-    """Verify Hermes never writes to ~/.codex/auth.json."""
+    """Verify _save_codex_tokens writes only to Hermes auth store, not ~/.codex/."""
     hermes_home = tmp_path / "hermes"
     codex_home = tmp_path / "codex-cli"
     hermes_home.mkdir(parents=True, exist_ok=True)
@@ -173,7 +174,7 @@ def test_codex_tokens_not_written_to_shared_file(tmp_path, monkeypatch):
 
     _save_codex_tokens({"access_token": "hermes-at", "refresh_token": "hermes-rt"})
 
-    # ~/.codex/auth.json should NOT exist
+    # ~/.codex/auth.json should NOT exist — _save_codex_tokens only touches Hermes store
     assert not (codex_home / "auth.json").exists()
 
     # Hermes auth store should have the tokens
@@ -181,6 +182,98 @@ def test_codex_tokens_not_written_to_shared_file(tmp_path, monkeypatch):
     assert data["tokens"]["access_token"] == "hermes-at"
 
 
+def test_write_codex_cli_tokens_creates_file(tmp_path, monkeypatch):
+    """_write_codex_cli_tokens creates ~/.codex/auth.json with refreshed tokens."""
+    codex_home = tmp_path / "codex-cli"
+    monkeypatch.setenv("CODEX_HOME", str(codex_home))
+
+    _write_codex_cli_tokens("new-access", "new-refresh", last_refresh="2026-04-12T00:00:00Z")
+
+    auth_path = codex_home / "auth.json"
+    assert auth_path.exists()
+    data = json.loads(auth_path.read_text())
+    assert data["tokens"]["access_token"] == "new-access"
+    assert data["tokens"]["refresh_token"] == "new-refresh"
+    assert data["last_refresh"] == "2026-04-12T00:00:00Z"
+    # Verify file permissions are restricted
+    assert (auth_path.stat().st_mode & 0o777) == 0o600
+
+
+def test_write_codex_cli_tokens_preserves_existing(tmp_path, monkeypatch):
+    """_write_codex_cli_tokens preserves extra fields in existing auth.json."""
+    codex_home = tmp_path / "codex-cli"
+    codex_home.mkdir(parents=True, exist_ok=True)
+    monkeypatch.setenv("CODEX_HOME", str(codex_home))
+
+    existing = {
+        "tokens": {
+            "access_token": "old-access",
+            "refresh_token": "old-refresh",
+            "extra_field": "preserved",
+        },
+        "last_refresh": "2026-01-01T00:00:00Z",
+        "custom_key": "keep_me",
+    }
+    (codex_home / "auth.json").write_text(json.dumps(existing))
+
+    _write_codex_cli_tokens("updated-access", "updated-refresh")
+
+    data = json.loads((codex_home / "auth.json").read_text())
+    assert data["tokens"]["access_token"] == "updated-access"
+    assert data["tokens"]["refresh_token"] == "updated-refresh"
+    assert data["tokens"]["extra_field"] == "preserved"
+    assert data["custom_key"] == "keep_me"
+    # last_refresh not updated since we didn't pass it
+    assert data["last_refresh"] == "2026-01-01T00:00:00Z"
+
+
+def test_write_codex_cli_tokens_handles_missing_dir(tmp_path, monkeypatch):
+    """_write_codex_cli_tokens creates parent directories if missing."""
+    codex_home = tmp_path / "does" / "not" / "exist"
+    monkeypatch.setenv("CODEX_HOME", str(codex_home))
+
+    _write_codex_cli_tokens("at", "rt")
+
+    assert (codex_home / "auth.json").exists()
+    data = json.loads((codex_home / "auth.json").read_text())
+    assert data["tokens"]["access_token"] == "at"
+
+
+def test_refresh_codex_auth_tokens_writes_back_to_cli(tmp_path, monkeypatch):
+    """After refreshing, _refresh_codex_auth_tokens writes back to ~/.codex/auth.json."""
+    from hermes_cli.auth import _refresh_codex_auth_tokens
+
+    hermes_home = tmp_path / "hermes"
+    codex_home = tmp_path / "codex-cli"
+    hermes_home.mkdir(parents=True, exist_ok=True)
+    codex_home.mkdir(parents=True, exist_ok=True)
+    (hermes_home / "auth.json").write_text(json.dumps({"version": 1, "providers": {}}))
+    monkeypatch.setenv("HERMES_HOME", str(hermes_home))
+    monkeypatch.setenv("CODEX_HOME", str(codex_home))
+
+    # Write initial CLI tokens
+    (codex_home / "auth.json").write_text(json.dumps({
+        "tokens": {"access_token": "old-at", "refresh_token": "old-rt"},
+    }))
+
+    # Mock the pure refresh to return new tokens
+    monkeypatch.setattr("hermes_cli.auth.refresh_codex_oauth_pure", lambda *a, **kw: {
+        "access_token": "refreshed-at",
+        "refresh_token": "refreshed-rt",
+        "last_refresh": "2026-04-12T01:00:00Z",
+    })
+
+    _refresh_codex_auth_tokens(
+        {"access_token": "old-at", "refresh_token": "old-rt"},
+        timeout_seconds=10,
+    )
+
+    # Verify CLI file was updated
+    cli_data = json.loads((codex_home / "auth.json").read_text())
+    assert cli_data["tokens"]["access_token"] == "refreshed-at"
+    assert cli_data["tokens"]["refresh_token"] == "refreshed-rt"
+
+
 def test_resolve_returns_hermes_auth_store_source(tmp_path, monkeypatch):
     hermes_home = tmp_path / "hermes"
     _setup_hermes_auth(hermes_home)