fix(picker): keep max_models=0 distinct from unlimited; lock cap semantics

Follow-up to the cap-removal salvage. The contributor guarded the new
unlimited default with `[:max_models] if max_models else ...`, which conflates
max_models=0 (used by slug-only callers that want an empty model list) with
None (unlimited). Tighten to `is not None` at all five slicing sites in
list_authenticated_providers / list_picker_providers, and add a regression test
asserting the three-way contract: None=full, 0=empty, N=first N.

hermes_cli/model_switch.py

@@ -1425,7 +1425,7 @@ def list_authenticated_providers(
             if hermes_id in _MODELS_DEV_PREFERRED:
                 model_ids = _merge_with_models_dev(hermes_id, model_ids)
         total = len(model_ids)
-        top = model_ids[:max_models] if max_models else model_ids
+        top = model_ids[:max_models] if max_models is not None else model_ids
 
         slug = hermes_id
         pinfo = _mdev_pinfo(mdev_id)
@@ -1588,7 +1588,7 @@ def list_authenticated_providers(
                 if hermes_slug in _MODELS_DEV_PREFERRED:
                     model_ids = _merge_with_models_dev(hermes_slug, model_ids)
         total = len(model_ids)
-        top = model_ids[:max_models] if max_models else model_ids
+        top = model_ids[:max_models] if max_models is not None else model_ids
 
         results.append({
             "slug": hermes_slug,
@@ -1663,7 +1663,7 @@ def list_authenticated_providers(
             if not _cp_model_ids:
                 _cp_model_ids = curated.get(_cp.slug, [])
         _cp_total = len(_cp_model_ids)
-        _cp_top = _cp_model_ids[:max_models] if max_models else _cp_model_ids
+        _cp_top = _cp_model_ids[:max_models] if max_models is not None else _cp_model_ids
 
         results.append({
             "slug": _cp.slug,
@@ -1812,7 +1812,7 @@ def list_authenticated_providers(
             "name": "Custom endpoint",
             "is_current": True,
             "is_user_defined": True,
-            "models": _models[:max_models] if max_models else _models,
+            "models": _models[:max_models] if max_models is not None else _models,
             "total_models": len(_models),
             "source": "model-config",
             "api_url": str(current_base_url).strip().rstrip("/"),
@@ -2082,7 +2082,7 @@ def list_picker_providers(
             except Exception:
                 live_ids = list(p.get("models", []))
             p = dict(p)
-            p["models"] = live_ids[:max_models] if max_models else live_ids
+            p["models"] = live_ids[:max_models] if max_models is not None else live_ids
             p["total_models"] = len(live_ids)
 
         has_models = bool(p.get("models"))

tests/hermes_cli/test_model_catalog.py

@@ -423,6 +423,71 @@ class TestIntegrationWithModelsModule:
         assert nous_row is not None, "nous row must appear when authed"
         assert nous_row["models"] == expected
 
+    def test_picker_max_models_cap_semantics(self, tmp_path, monkeypatch):
+        """The cap argument has three distinct meanings on the real slicing
+        path: ``None`` = unlimited (the cap-removal fix, #48297), ``0`` = no
+        models (preserved for slug-only callers), an int N = first N. Guards
+        the ``is not None`` distinction the cap-removal follow-up introduced —
+        a ``if max_models`` (falsy) check would conflate ``0`` with unlimited.
+        """
+        import importlib
+        from hermes_cli import model_catalog
+        from hermes_cli.models import get_curated_nous_model_ids
+        importlib.reload(model_catalog)
+        try:
+            from hermes_cli.model_switch import (
+                list_authenticated_providers,
+                list_picker_providers,
+            )
+
+            active_home = Path(os.environ["HERMES_HOME"])
+            (active_home / "auth.json").write_text(
+                json.dumps(
+                    {
+                        "providers": {"nous": {"access_token": "fake"}},
+                        "credential_pool": {},
+                    }
+                )
+            )
+            with patch.object(
+                model_catalog, "_fetch_manifest", return_value=_valid_manifest()
+            ), patch("hermes_cli.models.check_nous_free_tier", return_value=False), patch(
+                "hermes_cli.models.union_with_portal_free_recommendations",
+                side_effect=lambda ids, *a, **k: (ids, {}),
+            ), patch(
+                "hermes_cli.models.union_with_portal_paid_recommendations",
+                side_effect=lambda ids, *a, **k: (ids, {}),
+            ):
+                expected = get_curated_nous_model_ids()
+                full = list_picker_providers(current_provider="nous", max_models=None)
+                one = list_picker_providers(current_provider="nous", max_models=1)
+                # 0 is exercised on list_authenticated_providers (the slug-only
+                # path); the picker variant drops empty-model rows entirely, so
+                # the empty-list contract lives on the auth-providers call.
+                zero = list_authenticated_providers(
+                    current_provider="nous", max_models=0
+                )
+        finally:
+            model_catalog.reset_cache()
+
+        def _nous(rows):
+            return next((r for r in rows if r["slug"] == "nous"), None)
+
+        # Only meaningful when the curated list actually exceeds 1 entry.
+        assert len(expected) > 1, "test needs a multi-model curated nous list"
+
+        full_row = _nous(full)
+        assert full_row is not None and full_row["models"] == expected
+
+        one_row = _nous(one)
+        assert one_row is not None and one_row["models"] == expected[:1]
+
+        zero_row = _nous(zero)
+        # 0 means an empty model list — NOT unlimited. total_models still real.
+        assert zero_row is not None
+        assert zero_row["models"] == []
+        assert zero_row["total_models"] == len(expected)
+
 
 # -----------------------------------------------------------------------------
 # Drift guard — prevent the in-repo curated lists from going out of sync with