fix(gateway): honor per-provider max_output_tokens in max_tokens chain

Widens ViewWay's #20741 fix to the sibling config surface: a
custom_providers entry can pin its own output cap via max_output_tokens
(or max_tokens). _get_named_custom_provider now lifts it onto the
resolved runtime at all three return sites, and the gateway uses it as a
fallback only when the documented global model.max_tokens isn't set, so
the global key always wins.

Precedence: HERMES_MAX_TOKENS > model.max_tokens > provider
max_output_tokens > None. Closes the same #20741 truncation for users who
configure the cap per-provider rather than globally.

Picks up the intent of #19782 (alexcam1901), reimplemented to feed
ViewWay's max_tokens pipeline.

gateway/run.py

@@ -1213,6 +1213,13 @@ def _resolve_runtime_agent_kwargs() -> dict:
         mt = model_cfg.get("max_tokens")
         if isinstance(mt, int):
             max_tokens = mt
+    # Fall back to a per-provider output cap (custom_providers max_output_tokens)
+    # only when the documented global model.max_tokens isn't set, so the global
+    # key always wins.
+    if max_tokens is None:
+        _runtime_mot = runtime.get("max_output_tokens")
+        if isinstance(_runtime_mot, int) and _runtime_mot > 0:
+            max_tokens = _runtime_mot
 
     return {
         "api_key": runtime.get("api_key"),

hermes_cli/runtime_provider.py

@@ -474,6 +474,21 @@ def _try_resolve_from_custom_pool(
         return None
 
 
+def _lift_max_output_tokens(entry: Dict[str, Any], result: Dict[str, Any]) -> None:
+    """Propagate a per-provider output cap onto the resolved runtime dict.
+
+    Accepts ``max_output_tokens`` or ``max_tokens`` on a ``custom_providers``
+    entry so a provider block can pin its own output limit. Gateway and CLI
+    map this onto ``AIAgent.max_tokens`` only when the top-level
+    ``model.max_tokens`` isn't set, so the documented global key still wins.
+    """
+    for _k in ("max_output_tokens", "max_tokens"):
+        _v = entry.get(_k)
+        if isinstance(_v, int) and _v > 0:
+            result["max_output_tokens"] = _v
+            return
+
+
 def _get_named_custom_provider(requested_provider: str) -> Optional[Dict[str, Any]]:
     requested_norm = _normalize_custom_provider_name(requested_provider or "")
     if not requested_norm or requested_norm == "custom":
@@ -541,6 +556,7 @@ def _get_named_custom_provider(requested_provider: str) -> Optional[Dict[str, An
                     api_mode = _parse_api_mode(entry.get("api_mode") or entry.get("transport"))
                     if api_mode:
                         result["api_mode"] = api_mode
+                    _lift_max_output_tokens(entry, result)
                     return result
             # Also check the 'name' field if present
             display_name = entry.get("name", "")
@@ -562,6 +578,7 @@ def _get_named_custom_provider(requested_provider: str) -> Optional[Dict[str, An
                         api_mode = _parse_api_mode(entry.get("api_mode") or entry.get("transport"))
                         if api_mode:
                             result["api_mode"] = api_mode
+                        _lift_max_output_tokens(entry, result)
                         return result
 
     # Fall back to custom_providers: list (legacy format)
@@ -611,6 +628,7 @@ def _get_named_custom_provider(requested_provider: str) -> Optional[Dict[str, An
         model_name = str(entry.get("model", "") or "").strip()
         if model_name:
             result["model"] = model_name
+        _lift_max_output_tokens(entry, result)
         return result
 
     return None
@@ -699,6 +717,8 @@ def _resolve_named_custom_runtime(
         model_name = custom_provider.get("model")
         if model_name:
             pool_result["model"] = model_name
+        if isinstance(custom_provider.get("max_output_tokens"), int):
+            pool_result["max_output_tokens"] = custom_provider["max_output_tokens"]
         request_overrides = _custom_provider_request_overrides(custom_provider)
         if request_overrides:
             pool_result["request_overrides"] = {
@@ -736,6 +756,8 @@ def _resolve_named_custom_runtime(
     # provider name differs from the actual model string the API expects.
     if custom_provider.get("model"):
         result["model"] = custom_provider["model"]
+    if isinstance(custom_provider.get("max_output_tokens"), int):
+        result["max_output_tokens"] = custom_provider["max_output_tokens"]
     request_overrides = _custom_provider_request_overrides(custom_provider)
     if request_overrides:
         result["request_overrides"] = request_overrides