fix: opencode-go missing from /model list and improve HERMES_OVERLAYS credential check

When opencode-go API key is set, it should appear in the /model list.
The provider was already in PROVIDER_TO_MODELS_DEV and PROVIDER_REGISTRY,
so it appears via Part 1 (built-in source).

Also fixes a potential issue in Part 2 (HERMES_OVERLAYS) where providers
with auth_type=api_key but no extra_env_vars would not be detected:
- Now also checks api_key_env_vars from PROVIDER_REGISTRY for api_key auth_type

- Add test verifying opencode-go appears when OPENCODE_GO_API_KEY is set

hermes_cli/model_switch.py

@@ -809,8 +809,9 @@ def list_authenticated_providers(
         })
         seen_slugs.add(slug)
 
-    # --- 2. Check Hermes-only providers (nous, openai-codex, copilot) ---
+    # --- 2. Check Hermes-only providers (nous, openai-codex, copilot, opencode-go) ---
     from hermes_cli.providers import HERMES_OVERLAYS
+    from hermes_cli.auth import PROVIDER_REGISTRY as _auth_registry
     for pid, overlay in HERMES_OVERLAYS.items():
         if pid in seen_slugs:
             continue
@@ -818,6 +819,11 @@ def list_authenticated_providers(
         has_creds = False
         if overlay.extra_env_vars:
             has_creds = any(os.environ.get(ev) for ev in overlay.extra_env_vars)
+        # Also check api_key_env_vars from PROVIDER_REGISTRY for api_key auth_type
+        if not has_creds and overlay.auth_type == "api_key":
+            pcfg = _auth_registry.get(pid)
+            if pcfg and pcfg.api_key_env_vars:
+                has_creds = any(os.environ.get(ev) for ev in pcfg.api_key_env_vars)
         if overlay.auth_type in ("oauth_device_code", "oauth_external", "external_process"):
             # These use auth stores, not env vars — check for auth.json entries
             try:

tests/hermes_cli/test_opencode_go_in_model_list.py

@@ -0,0 +1,33 @@
+"""Test that opencode-go appears in /model list when credentials are set."""
+
+import os
+from unittest.mock import patch
+
+from hermes_cli.model_switch import list_authenticated_providers
+
+
+@patch.dict(os.environ, {"OPENCODE_GO_API_KEY": "test-key"}, clear=False)
+def test_opencode_go_appears_when_api_key_set():
+    """opencode-go should appear in list_authenticated_providers when OPENCODE_GO_API_KEY is set."""
+    providers = list_authenticated_providers(current_provider="openrouter")
+    
+    # Find opencode-go in results
+    opencode_go = next((p for p in providers if p["slug"] == "opencode-go"), None)
+    
+    assert opencode_go is not None, "opencode-go should appear when OPENCODE_GO_API_KEY is set"
+    assert opencode_go["models"] == ["glm-5", "kimi-k2.5", "mimo-v2-pro", "mimo-v2-omni", "minimax-m2.7", "minimax-m2.5"]
+    # opencode-go is in PROVIDER_TO_MODELS_DEV, so it appears as "built-in" (Part 1)
+    assert opencode_go["source"] == "built-in"
+
+
+def test_opencode_go_not_appears_when_no_creds():
+    """opencode-go should NOT appear when no credentials are set."""
+    # Ensure OPENCODE_GO_API_KEY is not set
+    env_without_key = {k: v for k, v in os.environ.items() if k != "OPENCODE_GO_API_KEY"}
+    
+    with patch.dict(os.environ, env_without_key, clear=True):
+        providers = list_authenticated_providers(current_provider="openrouter")
+        
+        # opencode-go should not be in results
+        opencode_go = next((p for p in providers if p["slug"] == "opencode-go"), None)
+        assert opencode_go is None, "opencode-go should not appear without credentials"