fix(aux): honour a custom OpenCode-family entry's declared api_mode, like the main runtime

opencode_transport() re-derived the wire for every OpenCode-family custom
entry, while hermes_cli/runtime_provider_custom.py::_resolve_named_custom_runtime
only re-derives when the entry declares no api_mode. Aux now mirrors that gate,
so an entry pinned to chat_completions stays a plain chat client on both paths.

Test grid trimmed to [None, one wrong mode]; the bridge fixture drops its
api_mode (the override no longer applies to it) and a pinned entry asserts the
honoured mode instead.

agent/opencode_affinity.py

@@ -35,12 +35,16 @@ def opencode_transport(provider: Optional[str], model: Optional[str], base_url:
     hosts all count.
     """
     from hermes_cli.models import normalize_opencode_base_url, normalize_opencode_model_id, opencode_model_api_mode
-    from hermes_cli.runtime_provider_custom import _opencode_family_for_custom
+    from hermes_cli.runtime_provider_custom import _get_named_custom_provider, _opencode_family_for_custom
 
     url = str(base_url or "")
     family = _opencode_family_for_custom(str(provider or ""), url)
     if family is None:
         return None, url
+    # A custom entry that declares its own api_mode keeps it, exactly like the main runtime
+    # (_resolve_named_custom_runtime only re-derives when the entry has none).
+    if (_get_named_custom_provider(str(provider or "")) or {}).get("api_mode"):
+        return None, url
     # ``<provider>/<model>`` config ids are stripped against the entry name before the family lookup.
     api_mode = opencode_model_api_mode(family, normalize_opencode_model_id(provider, model))
     return api_mode, normalize_opencode_base_url(provider, api_mode, url)

tests/agent/test_auxiliary_opencode_routing.py

@@ -25,6 +25,9 @@ def _isolated_home(tmp_path, monkeypatch):
         "  - name: opencode-go-bridge\n"
         "    base_url: https://opencode.ai/zen/go/v1\n"
         "    api_key: sk-bridge\n"
+        "  - name: opencode-go-pinned\n"
+        "    base_url: https://opencode.ai/zen/go/v1\n"
+        "    api_key: sk-pinned\n"
         "    api_mode: chat_completions\n"
     )
     return home
@@ -38,7 +41,7 @@ _WIRE_BY_MODEL = [
 
 
 @pytest.mark.parametrize("model, expected", _WIRE_BY_MODEL)
-@pytest.mark.parametrize("stale_api_mode", [None, "chat_completions", "codex_responses"])
+@pytest.mark.parametrize("stale_api_mode", [None, "chat_completions"])
 def test_builtin_opencode_go_client_follows_the_model_not_the_persisted_mode(model, expected, stale_api_mode):
     client, resolved = aux.resolve_provider_client("opencode-go", model=model, api_mode=stale_api_mode)
     assert resolved == model
@@ -49,7 +52,7 @@ def test_builtin_opencode_go_client_follows_the_model_not_the_persisted_mode(mod
 
 @pytest.mark.parametrize("model, expected", _WIRE_BY_MODEL)
 def test_named_custom_opencode_family_entry_follows_the_model(model, expected):
-    """An ``opencode-go-*`` custom entry persisted one api_mode at save time; each model still gets its own wire."""
+    """An ``opencode-go-*`` custom entry without an api_mode of its own gets each model's wire, like main."""
     client, resolved = aux.resolve_provider_client("custom:opencode-go-bridge", model=model)
     assert resolved == model
     assert type(client) is expected
@@ -58,3 +61,11 @@ def test_named_custom_opencode_family_entry_follows_the_model(model, expected):
     else:
         base = client._real_client.base_url if expected is aux.CodexAuxiliaryClient else client.base_url
         assert str(base).rstrip("/") == "https://opencode.ai/zen/go/v1"
+
+
+def test_named_custom_opencode_family_entry_with_declared_api_mode_is_honoured():
+    """An entry that declares ``api_mode`` keeps it — the main runtime only re-derives when the entry has none."""
+    client, resolved = aux.resolve_provider_client("custom:opencode-go-pinned", model="gpt-5.6-luna")
+    assert resolved == "gpt-5.6-luna"
+    assert type(client) is OpenAI
+    assert str(client.base_url).rstrip("/") == "https://opencode.ai/zen/go/v1"