feat(plugins): the model picker takes a title, public as prompt_model_selection

_prompt_model_selection gains title= (default 'Select default model:'), so a
plugin's route editor can say 'Select the model for this route:'. It is public
for plugins as hermes_cli.auth_model_picker.prompt_model_selection (listed in the
admission lint's public surfaces, with agent.delegation_backends) and documented
in the delegation provider guide.

hermes_cli/auth_model_picker.py

@@ -133,9 +133,8 @@ class _ModelPickerRows:
     def label(self, mid: str) -> str:
         return "".join(text for text, _style in self.segments(mid))
 
-    def menu_title(self) -> str:
-        """``Select default model:`` plus an aligned pricing header hint when priced."""
-        title = "Select default model:"
+    def menu_title(self, title: str = "Select default model:") -> str:
+        """*title* plus an aligned pricing header hint when priced."""
         if self.has_pricing:
             # Each choice is "  {label}" (2 spaces) plus a 3-char cursor region ("-> " or "   "),
             # so content starts at col 5.
@@ -155,9 +154,10 @@ def _prompt_model_selection(
     pricing: Optional[dict[str, dict[str, str]]] = None,
     unavailable_models: Optional[list[str]] = None, portal_url: str = "",
     unavailable_message: str = "", confirm_provider: str = "", confirm_base_url: str = "",
-    confirm_api_key: str = "", notes: Optional[dict[str, str]] = None,
+    confirm_api_key: str = "", notes: Optional[dict[str, str]] = None, title: str = "Select default model:",
 ) -> Optional[str]:
-    """Interactive model picker; current_model listed first. Returns the chosen model ID or None.
+    """Interactive model picker; current_model listed first. Returns the chosen model ID or None. *title* heads
+    the menu (a plugin picking a model for something other than the default says so).
 
     With *pricing* (``{model_id: {prompt, completion}}``) a compact price column is shown; models in
     *unavailable_models* render grayed out and unselectable with an upgrade link to *portal_url*.
@@ -194,7 +194,7 @@ def _prompt_model_selection(
     _DIM = "\033[2m"
     _RESET = "\033[0m"
 
-    menu_title = rows.menu_title()
+    menu_title = rows.menu_title(title)
     _upgrade_url = (portal_url or DEFAULT_NOUS_PORTAL_URL).rstrip("/")
     n = len(ordered)
 
@@ -223,7 +223,7 @@ def _prompt_model_selection(
         model_search_labels += [_CUSTOM_LABEL, _SKIP_LABEL]
 
         idx = curses_radiolist(
-            "Select default model:",
+            title,
             choices,
             selected=0,  # cursor on the current model (index 0 if it was reordered to top)
             cancel_returns=-1,
@@ -304,3 +304,7 @@ def _save_model_choice(model_id: str) -> None:
     from hermes_cli.observability.shared_metrics_setup import note_provider_setup_saved
 
     note_provider_setup_saved()
+
+
+# Public for plugins (catalog rule 9): the interactive model picker under a caller's title.
+prompt_model_selection = _prompt_model_selection

hermes_cli/plugin_validate_private_imports.py

@@ -27,7 +27,7 @@ from hermes_cli.plugin_validate_core_override import _hermes_top_level, _python_
 _PUBLIC = frozenset({
     # developer-guide / plugins docs
     "agent.account_usage", "agent.browser_provider", "agent.context_engine", "agent.credential_pool",
-    "agent.delegation_provider",
+    "agent.delegation_backends", "agent.delegation_provider", "hermes_cli.auth_model_picker:prompt_model_selection",
     "agent.image_gen_provider", "agent.memory_manager", "agent.memory_provider", "agent.secret_scope",
     "agent.secret_sources.base", "agent.subagent_lifecycle", "agent.terminal_env_provider",
     "agent.transports", "agent.transports.chat_completions", "agent.video_gen_provider",

website/docs/developer-guide/delegation-provider-plugin.md

@@ -159,7 +159,11 @@ uses:
 | `list_backends() -> list[BackendInfo]` | `default` first, then every registered backend: `name`, `label`, `description`, `available`, `reason` (the fix, when unavailable). |
 | `get_session_backend(session_key) -> str \| None` | The session's override, `None` when it follows `config.yaml`. |
 | `set_session_backend(session_key, name \| None)` | Switch one session (`None` clears). Raises `ValueError` with the reason for a backend that cannot run. |
-| `set_global_backend(name, *, session_key="")` | Write `delegation.backend` to the active profile's `config.yaml` and drop that session's override. |
+| `set_global_backend(name, *, session_key="")` | Write `delegation.backend` to the active profile's `config.yaml` and drop that session's override. Raises `PermissionError` on a package-manager-managed install. |
+
+A plugin command that edits model routes can reuse the interactive model picker under its own heading:
+`hermes_cli.auth_model_picker.prompt_model_selection(model_ids, current_model="", title="Select the model for this route:")`
+returns the chosen model id, or `None` when cancelled.
 
 `session_key` is the `session_key` a plugin command handler receives. A session switch decides routing
 from that session's next `delegate_task` call; the `delegate_task` schema (your parameters) follows