Fix custom provider identity loss in session persistence

_runtime_model_config persisted the live agent's RESOLVED provider into
the session row's model_config JSON. For any named providers:/
custom_providers: entry, agent.provider is the literal string "custom",
so the entry name was lost (and the api_key is deliberately never
persisted). On session.resume or _reset_session_agent the stored
provider="custom" fed resolve_runtime_provider(requested="custom"),
which cannot match a named entry — the rebuild either raised "No LLM
provider configured" or silently resolved placeholder credentials
against the patched-back base_url.

Persist the REQUESTED/entry identity instead: a new reverse lookup
find_custom_provider_identity(base_url) maps the endpoint URL back to
the canonical custom:<name> menu key. _runtime_model_config stores that
key; _make_agent performs the same recovery for rows persisted before
the fix, falling back to passing the stored base_url as
explicit_base_url so the direct-alias branch still targets the
session's endpoint when no entry matches.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

hermes_cli/runtime_provider.py

@@ -660,6 +660,61 @@ def has_named_custom_provider(requested_provider: str) -> bool:
         return False
 
 
+def find_custom_provider_identity(base_url: str) -> Optional[str]:
+    """Map an endpoint URL back to its canonical ``custom:<name>`` menu key.
+
+    Returns the ``custom:<normalized-name>`` slug of the first ``providers:``
+    / ``custom_providers:`` entry whose base_url matches, or ``None`` when no
+    entry owns the URL.
+
+    Session persistence stores the agent's *resolved* provider, and for every
+    named custom endpoint that is the literal string ``"custom"`` — the entry
+    name is lost, and the api_key is deliberately never persisted. The
+    endpoint URL is the one durable fact that survives the round-trip, so
+    this reverse lookup lets persist/rebuild paths recover the entry identity
+    (and with it key_env/api_key/api_mode resolution via
+    :func:`_get_named_custom_provider`) instead of failing with
+    ``auth_unavailable`` or silently rebuilding with placeholder credentials.
+    """
+    target = _normalize_base_url_for_match(base_url)
+    if not target:
+        return None
+    try:
+        config = load_config()
+    except Exception:
+        return None
+
+    providers = config.get("providers")
+    if isinstance(providers, dict):
+        for ep_name, entry in providers.items():
+            if not isinstance(entry, dict):
+                continue
+            entry_url = (
+                entry.get("api") or entry.get("url") or entry.get("base_url") or ""
+            )
+            if _normalize_base_url_for_match(entry_url) == target:
+                return f"custom:{_normalize_custom_provider_name(str(ep_name))}"
+
+    try:
+        custom_providers = get_compatible_custom_providers(config)
+    except Exception:
+        custom_providers = None
+    for entry in custom_providers or []:
+        if not isinstance(entry, dict):
+            continue
+        name = entry.get("name")
+        if not isinstance(name, str) or not name.strip():
+            continue
+        if _normalize_base_url_for_match(entry.get("base_url")) == target:
+            return f"custom:{_normalize_custom_provider_name(name)}"
+
+    return None
+
+
+def _normalize_base_url_for_match(value) -> str:
+    return str(value or "").strip().rstrip("/").lower()
+
+
 def _custom_provider_request_overrides(custom_provider: Dict[str, Any]) -> Dict[str, Any]:
     extra_body = custom_provider.get("extra_body")
     if not isinstance(extra_body, dict) or not extra_body: