test(quality): fix fake tests and add missing coverage

P0 fixes:
- telemetry: rewrite fake tests with real behavior verification (25 tests)
- config: delete copied-source tests, use proper imports (2 deleted)
- persistence: fix try-except pass to verify specific errors

P1 fixes:
- pipeline: add real FixedWindowAlgo tests instead of mocks (12 tests)
- provider: add SessionManager and ToolManager tests (25 tests)
- storage: add S3StorageProvider tests with moto mock (16 tests)
- plugin: add handler action tests for setting inheritance (15 tests)
- rag: add file storage and ZIP processing tests (21 tests)
- vector: add VDB filter conversion tests (30 tests)

P2 fixes:
- pipeline/msgtrun: strengthen assertions for exact message count
- api: add response structure validation in integration tests

New test files:
- provider/test_session_manager.py
- provider/test_tool_manager.py
- storage/test_s3storage.py
- plugin/test_handler_actions.py
- rag/test_file_storage.py
- vector/test_vdb_filter_conversion.py

Source code bugs documented:
- provider: TokenManager.next_token() ZeroDivisionError
- telemetry: send_tasks class variable shared state
- command: empty command IndexError, unused parameters
- utils: funcschema KeyError
- entity: vector.py independent declarative_base

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/unit_tests/core/test_load_config.py

@@ -263,4 +263,28 @@ class TestApplyEnvOverridesToConfig:
 
         assert result['system']['name'] == 'custom'
         assert result['system']['enable'] is False
-        assert result['concurrency']['pipeline'] == 10
+        assert result['concurrency']['pipeline'] == 10
+
+    def test_webhook_prefix_override(self):
+        """Test overriding webhook_prefix via environment variable."""
+        load_config = get_load_config_module()
+
+        cfg = {'api': {'port': 5300, 'webhook_prefix': 'http://127.0.0.1:5300', 'extra_webhook_prefix': ''}}
+        env = {'API__WEBHOOK_PREFIX': 'https://example.com:8080'}
+
+        with patch.dict(os.environ, env, clear=True):
+            result = load_config._apply_env_overrides_to_config(cfg)
+
+        assert result['api']['webhook_prefix'] == 'https://example.com:8080'
+
+    def test_extra_webhook_prefix_override(self):
+        """Test overriding extra_webhook_prefix via environment variable."""
+        load_config = get_load_config_module()
+
+        cfg = {'api': {'port': 5300, 'webhook_prefix': 'http://127.0.0.1:5300', 'extra_webhook_prefix': ''}}
+        env = {'API__EXTRA_WEBHOOK_PREFIX': 'https://extra.example.com'}
+
+        with patch.dict(os.environ, env, clear=True):
+            result = load_config._apply_env_overrides_to_config(cfg)
+
+        assert result['api']['extra_webhook_prefix'] == 'https://extra.example.com'