fix(moa): disabled presets no longer hijack a plain model switch (#55598)

exact_moa_preset_name matched any bare model name equal to a preset key,
regardless of the preset's enabled flag. On the no-explicit-provider switch
path (PATH B in model_switch.py), a plain /model switch whose name collided
with a preset key (e.g. "default") silently pivoted the session onto the MoA
virtual provider — even when the user had set enabled: false to opt out
(issue #55187). The LLM driving a routine model switch could land on a broken
moa provider with empty default_preset / unconfigured aggregator credentials.

Gate the implicit bare-name match on the per-preset enabled flag. Explicit
selection via --provider moa / the model picker uses PATH A and does not go
through exact_moa_preset_name, so a disabled preset stays reachable when the
user explicitly asks for it.

hermes_cli/moa_config.py

@@ -158,11 +158,26 @@ def resolve_moa_preset(config: Any, name: str | None = None) -> dict[str, Any]:
 
 
 def exact_moa_preset_name(config: Any, text: str) -> str | None:
+    """Return the preset name iff ``text`` exactly matches an *enabled* preset.
+
+    Used by the no-explicit-provider switch path (PATH B in
+    ``hermes_cli/model_switch.py``) to recognize a bare ``/model <preset>``
+    that the user typed without the ``moa:`` prefix. This is an *implicit*
+    match, so it must honor the per-preset ``enabled`` opt-out: a user who set
+    ``enabled: false`` to disable a preset must not have a plain model switch
+    whose name happens to collide with that preset key silently pivot the
+    session onto the MoA virtual provider (issue #55187). Explicit selection
+    via ``--provider moa`` / the model picker does not go through here, so a
+    disabled preset is still reachable when the user explicitly asks for it.
+    """
     wanted = str(text or "").strip()
     if not wanted:
         return None
     cfg = normalize_moa_config(config)
-    return wanted if wanted in cfg["presets"] else None
+    preset = cfg["presets"].get(wanted)
+    if preset is None or not preset.get("enabled", True):
+        return None
+    return wanted
 
 
 def set_active_moa_preset(config: Any, name: str | None) -> dict[str, Any]:

tests/hermes_cli/test_moa_config.py

@@ -120,6 +120,38 @@ def test_exact_preset_matching_is_not_fuzzy():
     assert exact_moa_preset_name(config, "coding please fix this") is None
 
 
+def test_exact_preset_matching_skips_disabled_presets():
+    """A disabled preset must not match the implicit bare-name switch path.
+
+    Regression for #55187: with ``enabled: false`` presets, a plain model
+    switch whose name collides with a preset key (e.g. ``default``) silently
+    pivoted the session onto the MoA virtual provider. The per-preset
+    ``enabled`` opt-out must gate this implicit match.
+    """
+    config = {
+        "presets": {
+            "default": {"enabled": False},
+            "klo": {"enabled": False},
+        },
+    }
+    assert exact_moa_preset_name(config, "default") is None
+    assert exact_moa_preset_name(config, "klo") is None
+
+
+def test_exact_preset_matching_allows_enabled_presets():
+    """An explicitly enabled preset still matches the bare-name switch path."""
+    config = {
+        "presets": {
+            "fast": {"enabled": True},
+            "slow": {"enabled": False},
+        },
+    }
+    assert exact_moa_preset_name(config, "fast") == "fast"
+    assert exact_moa_preset_name(config, "slow") is None
+    # Default (no explicit enabled key) is enabled and still matches.
+    assert exact_moa_preset_name({"presets": {"x": {}}}, "x") == "x"
+
+
 def test_active_preset_toggle_validation():
     config = {"default_preset": "coding", "presets": {"coding": {}, "review": {}}}