fix(delegation): preserve configured_provider name when runtime returns 'custom'

Named custom providers (e.g. crof.ai) resolve to provider='custom' at the
runtime level, causing subagents to lose their intended provider identity.
On retry/fallback, resolve_provider_client('custom', model=...) searches all
providers advertising that model and picks non-deterministically, routing to
Z.AI or Bailian instead of the configured target.

The fix preserves configured_provider when runtime['provider'] == 'custom',
restoring the original provider name so routing stays correct through retries.
Adds a named constant _RUNTIME_PROVIDER_CUSTOM instead of a magic string.

Adds three regression tests:
- test_named_custom_provider_preserves_provider_name: the #26954 case
- test_standard_provider_not_overwritten_by_configured_name: openrouter/nous
  must still return their own identity, not the configured name
- test_custom_provider_with_empty_configured_provider_falls_back_to_runtime:
  empty provider triggers the early-return None path as before

tests/tools/test_delegate.py

@@ -1014,6 +1014,71 @@ class TestDelegationCredentialResolution(unittest.TestCase):
         self.assertIsNone(creds["model"])
         self.assertIsNone(creds["provider"])
 
+    @patch("hermes_cli.runtime_provider.resolve_runtime_provider")
+    def test_named_custom_provider_preserves_provider_name(self, mock_resolve):
+        """Named custom provider (e.g. crof.ai) resolves to 'custom' at runtime level
+        but the subagent must retain the original provider identity so that
+        resolve_provider_client routes to the correct endpoint on retry/fallback.
+        Regression test for #26954.
+        """
+        mock_resolve.return_value = {
+            "provider": "custom",  # runtime marks it as "custom" type
+            "model": "deepseek-v4-pro-CEER",
+            "base_url": "https://api.crof.ai/v1",
+            "api_key": "crof-key-abc",
+            "api_mode": "chat_completions",
+        }
+        parent = _make_mock_parent(depth=0)
+        cfg = {"model": "deepseek-v4-pro-CEER", "provider": "crof.ai"}
+        creds = _resolve_delegation_credentials(cfg, parent)
+        # The key assertion: subagent must keep "crof.ai", NOT "custom"
+        self.assertEqual(creds["provider"], "crof.ai")
+        self.assertEqual(creds["model"], "deepseek-v4-pro-CEER")
+        self.assertEqual(creds["base_url"], "https://api.crof.ai/v1")
+        self.assertEqual(creds["api_key"], "crof-key-abc")
+        # Verify resolve_runtime_provider was called with the configured name
+        mock_resolve.assert_called_once_with(
+            requested="crof.ai", target_model="deepseek-v4-pro-CEER"
+        )
+
+    @patch("hermes_cli.runtime_provider.resolve_runtime_provider")
+    def test_standard_provider_not_overwritten_by_configured_name(self, mock_resolve):
+        """Standard (non-custom) providers must still return runtime identity,
+        not the configured name, to preserve existing behaviour for openrouter,
+        nous, etc.
+        """
+        mock_resolve.return_value = {
+            "provider": "openrouter",
+            "model": "anthropic/claude-sonnet-4",
+            "base_url": "https://openrouter.ai/api/v1",
+            "api_key": "or-key-xyz",
+            "api_mode": "chat_completions",
+        }
+        parent = _make_mock_parent(depth=0)
+        cfg = {"model": "anthropic/claude-sonnet-4", "provider": "openrouter"}
+        creds = _resolve_delegation_credentials(cfg, parent)
+        # Standard provider returns its own name, not "custom"
+        self.assertEqual(creds["provider"], "openrouter")
+
+    @patch("hermes_cli.runtime_provider.resolve_runtime_provider")
+    def test_custom_provider_with_empty_configured_provider_falls_back_to_runtime(self, mock_resolve):
+        """When configured_provider is empty/None, the early return kicks in and
+        we return provider=None regardless of what runtime resolved. The runtime
+        path is only reached when configured_provider is a non-empty string.
+        """
+        mock_resolve.return_value = {
+            "provider": "custom",
+            "model": "some-model",
+            "base_url": "https://fallback.example.com/v1",
+            "api_key": "key-fallback",
+            "api_mode": "chat_completions",
+        }
+        parent = _make_mock_parent(depth=0)
+        cfg = {"model": "some-model", "provider": ""}
+        creds = _resolve_delegation_credentials(cfg, parent)
+        # Empty provider → early return with None (child inherits parent)
+        self.assertIsNone(creds["provider"])
+
 
 class TestDelegationProviderIntegration(unittest.TestCase):
     """Integration tests: delegation config → _run_single_child → AIAgent construction."""

tools/delegate_tool.py

@@ -31,6 +31,11 @@ from concurrent.futures import (
 from typing import Any, Dict, List, Optional
 
 from toolsets import TOOLSETS
+
+# Sentinel value used by the runtime provider system for providers that are
+# not natively known (named custom providers, third-party aggregators, etc.).
+# Must match hermes_cli.runtime_provider.RUNTIME_PROVIDER_TYPE_CUSTOM.
+_RUNTIME_PROVIDER_CUSTOM = "custom"
 from tools import file_state
 from tools.terminal_tool import set_approval_callback as _set_subagent_approval_cb
 from utils import base_url_hostname, is_truthy_value
@@ -2442,7 +2447,7 @@ def _resolve_delegation_credentials(cfg: dict, parent_agent) -> dict:
 
     return {
         "model": configured_model or runtime.get("model") or None,
-        "provider": runtime.get("provider"),
+        "provider": configured_provider if runtime.get("provider") == _RUNTIME_PROVIDER_CUSTOM else runtime.get("provider"),
         "base_url": runtime.get("base_url"),
         "api_key": api_key,
         "api_mode": runtime.get("api_mode"),