feat(skill): unify skill activation as authorized tools

Expose skill tools (activate/register_skill/native exec) like native tools
instead of gating them behind the skill_authoring capability:
- toolmgr.get_all_tools drops include_skill_authoring; SkillToolLoader
  self-gates on sandbox + skill_mgr
- preproc drops the include_skill_authoring branch; pipeline-bound skills
  and the skills resource gate on skill_mgr presence

Persist activated skills into host.activated_skills conversation state so
they survive across runs (host writes at activate; last-write-wins); drop
the dead restore_activated_skills helper.

Prefill ToolResource.parameters host-side (tool_mgr.get_tool_schema) so
runners build LLM tools without per-tool get_tool_detail round-trips.

Align agent-runner-pluginization design docs to the all-tool model.

tests/unit_tests/provider/test_skill_tools.py

@@ -176,6 +176,63 @@ class TestSkillActivationHelper:
         assert register_activated_skill(ap, query, 'primary') is False
 
 
+class TestPersistActivatedSkill:
+    """Host-side persistence of activated skills into conversation state (S-01/S-02)."""
+
+    @pytest.mark.asyncio
+    async def test_persist_writes_conversation_state(self):
+        from unittest.mock import patch
+        from langbot.pkg.provider.tools.loaders.skill import (
+            persist_activated_skill,
+            ACTIVATED_SKILLS_KEY,
+            ACTIVATED_SKILL_NAMES_STATE_KEY,
+        )
+
+        ap = _make_ap()
+        ap.persistence_mgr.get_db_engine = Mock(return_value=Mock())
+
+        query = SimpleNamespace(variables={ACTIVATED_SKILLS_KEY: {'pdf': {'name': 'pdf'}}})
+        query._agent_run_session = {
+            'runner_id': 'plugin:langbot/local-agent/default',
+            'state_context': {
+                'scope_keys': {'conversation': 'conv-scope-key'},
+                'binding_identity': 'binding-1',
+                'conversation_id': 'c1',
+            },
+        }
+
+        store = SimpleNamespace(state_set=AsyncMock(return_value=(True, None)))
+        with patch(
+            'langbot.pkg.agent.runner.persistent_state_store.get_persistent_state_store',
+            return_value=store,
+        ):
+            await persist_activated_skill(ap, query, 'pdf')
+
+        store.state_set.assert_awaited_once()
+        kwargs = store.state_set.await_args.kwargs
+        assert kwargs['scope_key'] == 'conv-scope-key'
+        assert kwargs['state_key'] == ACTIVATED_SKILL_NAMES_STATE_KEY
+        assert kwargs['value'] == ['pdf']
+        assert kwargs['scope'] == 'conversation'
+        assert kwargs['runner_id'] == 'plugin:langbot/local-agent/default'
+        assert kwargs['binding_identity'] == 'binding-1'
+
+    @pytest.mark.asyncio
+    async def test_persist_noop_without_run_session(self):
+        from unittest.mock import patch
+        from langbot.pkg.provider.tools.loaders.skill import persist_activated_skill
+
+        ap = _make_ap()
+        query = SimpleNamespace(variables={'_activated_skills': {'pdf': {'name': 'pdf'}}})
+
+        with patch(
+            'langbot.pkg.agent.runner.persistent_state_store.get_persistent_state_store',
+        ) as mock_factory:
+            await persist_activated_skill(ap, query, 'pdf')
+
+        mock_factory.assert_not_called()
+
+
 class TestSkillPathHelpers:
     def test_get_visible_skills_filters_by_bound_names(self):
         from langbot.pkg.provider.tools.loaders.skill import PIPELINE_BOUND_SKILLS_KEY, get_visible_skills
@@ -193,12 +250,13 @@ class TestSkillPathHelpers:
 
         assert list(result.keys()) == ['visible']
 
-    def test_restore_activated_skills_uses_caller_provided_names_and_visibility(self):
+    def test_restore_activated_skills_from_state_filters_by_visibility(self):
         from langbot.pkg.provider.tools.loaders.skill import (
             ACTIVATED_SKILLS_KEY,
+            ACTIVATED_SKILL_NAMES_STATE_KEY,
             PIPELINE_BOUND_SKILLS_KEY,
             get_activated_skill_names,
-            restore_activated_skills,
+            restore_activated_skills_from_state,
         )
 
         ap = _make_ap()
@@ -209,8 +267,9 @@ class TestSkillPathHelpers:
             }
         )
         query = SimpleNamespace(variables={PIPELINE_BOUND_SKILLS_KEY: ['visible']})
+        state = {'conversation': {ACTIVATED_SKILL_NAMES_STATE_KEY: ['visible', 'hidden', 'visible', '']}}
 
-        restored = restore_activated_skills(ap, query, ['visible', 'hidden', 'visible', ''])
+        restored = restore_activated_skills_from_state(ap, query, state)
 
         assert restored == ['visible']
         assert list(query.variables[ACTIVATED_SKILLS_KEY].keys()) == ['visible']