fix(plugins): clear _plugin_platform_names on force-rediscover

discover_and_load(force=True) cleared every per-plugin registry except
_plugin_platform_names, which register_platform() populates. A platform
plugin disabled between force-rediscovers left a stale name behind, so the
set diverged from the real platform_registry / _plugins state and never
shrank across repeated force passes.

Add the missing clear() and a regression test that seeds every per-plugin
registry, forces a rediscover, and asserts they all empty (so a future
registry addition can't silently leak across a force pass either).

hermes_cli/plugins.py

@@ -1129,6 +1129,7 @@ class PluginManager:
             self._hooks.clear()
             self._middleware.clear()
             self._plugin_tool_names.clear()
+            self._plugin_platform_names.clear()
             self._cli_commands.clear()
             self._plugin_commands.clear()
             self._plugin_skills.clear()

tests/hermes_cli/test_plugins.py

@@ -439,6 +439,50 @@ class TestPluginDiscovery:
 
         assert "ep_plugin" in mgr._plugins
 
+    def test_force_rediscover_clears_all_plugin_registries(self, monkeypatch):
+        """force=True must clear every plugin-populated registry.
+
+        Regression: ``_plugin_platform_names`` was populated by
+        ``register_platform`` but omitted from the ``discover_and_load(force=True)``
+        clear block, so a platform plugin disabled between force-rediscovers
+        left a stale entry behind forever (the set diverged from the real
+        platform_registry / _plugins truth). This asserts the clear block
+        empties the full set of per-plugin registries so no future addition
+        silently leaks across a force pass either.
+        """
+        mgr = PluginManager()
+
+        # Seed every registry that a plugin's register() can populate, then
+        # mark discovery done so force=True takes the clear path (we stub the
+        # inner sweep so the test doesn't depend on any on-disk plugins).
+        mgr._plugins["p"] = MagicMock()
+        mgr._hooks["pre_tool_call"] = [lambda **_: None]
+        mgr._middleware["llm_request"] = [lambda **_: None]
+        mgr._plugin_tool_names.add("some_tool")
+        mgr._plugin_platform_names.add("irc")
+        mgr._cli_commands["c"] = {"plugin": "p"}
+        mgr._plugin_commands["cmd"] = {"plugin": "p"}
+        mgr._plugin_skills["p:skill"] = {}
+        mgr._aux_tasks["task"] = {"plugin": "p"}
+        mgr._slack_action_handlers.append(("aid", lambda **_: None, "p"))
+        mgr._discovered = True
+
+        monkeypatch.setattr(PluginManager, "_discover_and_load_inner", lambda self_inner: None)
+        mgr.discover_and_load(force=True)
+
+        assert mgr._plugins == {}
+        assert mgr._hooks == {}
+        assert mgr._middleware == {}
+        assert mgr._plugin_tool_names == set()
+        assert mgr._plugin_platform_names == set(), (
+            "_plugin_platform_names was not cleared on force-rediscover"
+        )
+        assert mgr._cli_commands == {}
+        assert mgr._plugin_commands == {}
+        assert mgr._plugin_skills == {}
+        assert mgr._aux_tasks == {}
+        assert mgr._slack_action_handlers == []
+
 
 # ── TestPluginLoading ──────────────────────────────────────────────────────