feat(telemetry): payload v2 with feature usage counters and instance heartbeat

Per-query events now carry event_type='query' and a features JSON object:
- tool_calls by source (native/plugin/mcp/skill) via ToolManager
- tool_call_rounds, kb usage (count/engine plugins/retrieved entries) via local-agent
- sandbox execs/errors via BoxService
- activated_skills and bound mcp_servers snapshots

New instance_heartbeat event (startup + daily) reports anonymous instance
profile: deploy platform, database/vdb kind, box backend/availability,
adapter type names, and resource counts. Respects space.disable_telemetry.

All collection helpers are defensive and never break the pipeline.
Verified: ruff, 37 telemetry unit tests (13 new), 504 box/provider/pipeline tests.

tests/unit_tests/telemetry/test_heartbeat.py

@@ -0,0 +1,104 @@
+"""Unit tests for telemetry heartbeat payload (pkg/telemetry/heartbeat.py)."""
+
+from __future__ import annotations
+
+import json
+
+import pytest
+from unittest.mock import AsyncMock, Mock
+from importlib import import_module
+
+
+def get_heartbeat_module():
+    return import_module('langbot.pkg.telemetry.heartbeat')
+
+
+def make_app():
+    ap = Mock()
+    ap.instance_config = Mock()
+    ap.instance_config.data = {
+        'database': {'use': 'postgresql'},
+        'vdb': {'use': 'chroma'},
+        'box': {'enabled': True, 'backend': 'nsjail'},
+    }
+
+    # persistence counts
+    result = Mock()
+    result.scalar.return_value = 3
+    ap.persistence_mgr = Mock()
+    ap.persistence_mgr.execute_async = AsyncMock(return_value=result)
+
+    # box service
+    ap.box_service = Mock()
+    ap.box_service.enabled = True
+    ap.box_service.available = False
+    ap.box_service.shares_filesystem_with_box = False
+
+    # platform manager with one enabled bot
+    bot = Mock()
+    bot.enable = True
+    bot.adapter = Mock()
+    bot.adapter.__class__.__name__ = 'TelegramAdapter'
+    ap.platform_mgr = Mock()
+    ap.platform_mgr.bots = [bot]
+
+    # plugin connector
+    ap.plugin_connector = Mock()
+    ap.plugin_connector.list_plugins = AsyncMock(return_value=[{}, {}])
+
+    # skills
+    ap.skill_mgr = Mock()
+    ap.skill_mgr.skills = {'a': {}, 'b': {}, 'c': {}}
+
+    return ap
+
+
+class TestBuildHeartbeatPayload:
+    @pytest.mark.asyncio
+    async def test_payload_shape(self):
+        heartbeat = get_heartbeat_module()
+        ap = make_app()
+        payload = await heartbeat.build_heartbeat_payload(ap)
+
+        assert payload['event_type'] == 'instance_heartbeat'
+        assert payload['query_id'] == ''
+        assert 'timestamp' in payload
+        f = payload['features']
+        assert f['database'] == 'postgresql'
+        assert f['vdb'] == 'chroma'
+        assert f['box'] == {
+            'enabled': True,
+            'available': False,
+            'backend': 'nsjail',
+            'shares_fs': False,
+        }
+        assert f['adapters'] == ['TelegramAdapter']
+        assert f['bot_count'] == 1
+        assert f['plugin_count'] == 2
+        assert f['skill_count'] == 3
+        assert f['pipeline_count'] == 3
+        assert f['mcp_server_count'] == 3
+        assert f['knowledge_base_count'] == 3
+
+    @pytest.mark.asyncio
+    async def test_payload_is_json_serializable(self):
+        heartbeat = get_heartbeat_module()
+        payload = await heartbeat.build_heartbeat_payload(make_app())
+        json.dumps(payload)
+
+    @pytest.mark.asyncio
+    async def test_count_failure_yields_minus_one(self):
+        heartbeat = get_heartbeat_module()
+        ap = make_app()
+        ap.persistence_mgr.execute_async = AsyncMock(side_effect=RuntimeError('db down'))
+        payload = await heartbeat.build_heartbeat_payload(ap)
+        assert payload['features']['pipeline_count'] == -1
+
+    @pytest.mark.asyncio
+    async def test_no_user_content_fields(self):
+        """The heartbeat must never carry message content / credentials keys."""
+        heartbeat = get_heartbeat_module()
+        payload = await heartbeat.build_heartbeat_payload(make_app())
+        flat = json.dumps(payload).lower()
+        for forbidden in ('api_key', 'password', 'token', 'message_content'):
+            assert forbidden not in flat