fix(runtime_provider): _get_named_custom_provider must honour transport field on v12+ providers dict

The v11→v12 migrate_config step writes the API mode for every entry
under the new transport: field (per the v12+ schema in
_normalize_custom_provider_entry).  _get_named_custom_provider
read the legacy api_mode: spelling only, so for every migrated
config the lookup returned None for the api mode.

Downstream, _resolve_named_custom_runtime then falls back through
custom_provider.get("api_mode") or _detect_api_mode_for_url(base_url)
or "chat_completions".  For loopback URLs (proxies, local servers)
or unknown hostnames, the URL detector returns None and the resolver
silently downgrades the configured codex_responses /
anthropic_messages transport to chat_completions.  Requests
get sent to /v1/chat/completions instead of /v1/responses or
/v1/messages and the provider 404s — or worse, returns a usable
chat_completions response while skipping the model's reasoning /
caching surface.

Fix: read both field names — entry.get("api_mode") or
entry.get("transport") — at the two match-by-key + match-by-name
branches in _get_named_custom_provider.  The runtime normaliser
_normalize_custom_provider_entry already accepts both spellings;
this lifts the same compat into the direct-dict reader so v12+
configs work without going through the shim.

Adds three regression tests under
tests/hermes_cli/test_user_providers_model_switch.py:
- transport field is read on the match-by-key branch
- legacy api_mode spelling still works for hand-edited configs
- transport is read on the match-by-display-name branch

tests/hermes_cli/test_user_providers_model_switch.py

@@ -748,6 +748,94 @@ def test_switch_model_resolves_user_provider_credentials(monkeypatch, tmp_path):
         is_global=False,
         user_providers=config["providers"],
     )
-    
+
     assert result.success is True
     assert result.error_message == ""
+
+
+# =============================================================================
+# Regression: providers: dict ``transport`` field must be honored
+# =============================================================================
+
+
+def test_get_named_custom_provider_reads_transport_field(monkeypatch):
+    """v12+ ``providers:`` dict stores api mode under ``transport:`` (not the
+    legacy ``api_mode:``).  ``_get_named_custom_provider`` must accept both
+    field names.
+
+    Bug: this function read only ``entry.get("api_mode")`` for v12+ entries.
+    After ``migrate_config()`` writes ``transport`` on every entry, the
+    lookup returns None and ``_resolve_named_custom_runtime`` falls back
+    through ``_detect_api_mode_for_url(base_url) or "chat_completions"``
+    — silently downgrading every codex_responses / anthropic_messages
+    provider to chat_completions.
+    """
+    config = {
+        "_config_version": 12,
+        "providers": {
+            "my-codex-provider": {
+                "name": "my-codex-provider",
+                "api": "http://127.0.0.1:4000/v1",
+                "api_key": "test-key",
+                "default_model": "gpt-5",
+                "transport": "codex_responses",
+            },
+        },
+    }
+
+    monkeypatch.setattr(rp, "load_config", lambda: config)
+
+    result = rp._get_named_custom_provider("my-codex-provider")
+    assert result is not None
+    assert result["api_mode"] == "codex_responses"
+    assert result["base_url"] == "http://127.0.0.1:4000/v1"
+    assert result["model"] == "gpt-5"
+
+
+def test_get_named_custom_provider_legacy_api_mode_field_still_works(monkeypatch):
+    """Hand-edited configs that used ``api_mode:`` (legacy spelling) inside
+    the v12+ providers: dict shape must keep working — the migration writer
+    produces ``transport:`` but human-edited configs may carry the older
+    spelling forward."""
+    config = {
+        "_config_version": 12,
+        "providers": {
+            "anthropic-proxy": {
+                "name": "anthropic-proxy",
+                "api": "http://127.0.0.1:8082",
+                "api_key": "test-key",
+                "default_model": "claude-opus-4-7",
+                "api_mode": "anthropic_messages",  # legacy spelling
+            },
+        },
+    }
+
+    monkeypatch.setattr(rp, "load_config", lambda: config)
+
+    result = rp._get_named_custom_provider("anthropic-proxy")
+    assert result is not None
+    assert result["api_mode"] == "anthropic_messages"
+
+
+def test_get_named_custom_provider_transport_resolves_via_display_name(monkeypatch):
+    """When the requested name matches the entry's ``name:`` field rather
+    than its dict key, the same transport-vs-api_mode logic must apply
+    (second branch in ``_get_named_custom_provider``)."""
+    config = {
+        "_config_version": 12,
+        "providers": {
+            "slug-different-from-name": {
+                "name": "Codex Provider",  # display name
+                "api": "http://127.0.0.1:4000/v1",
+                "api_key": "test-key",
+                "default_model": "gpt-5",
+                "transport": "codex_responses",
+            },
+        },
+    }
+
+    monkeypatch.setattr(rp, "load_config", lambda: config)
+
+    result = rp._get_named_custom_provider("Codex Provider")
+    assert result is not None
+    assert result["api_mode"] == "codex_responses"