fix: centralized pipeline config type coercion to prevent string-type crashes (#2031)

* fix: coerce pipeline config types at load time using metadata definitions

Pipeline configs stored in SQLAlchemy JSON columns can have values turned
into strings after UI edits (e.g. "120" instead of 120), causing runtime
arithmetic/logic errors. Add centralized type coercion in load_pipeline()
that leverages existing metadata YAML type definitions (integer, number,
float, boolean) to convert values before they reach downstream stages.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: address review - defensive getattr + add unit tests for config_coercion

- Use getattr with defaults for pipeline_config_meta_* attributes to
  avoid AttributeError when MockApplication lacks these fields
- Add 18 unit tests for config_coercion module covering all code paths

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add dynamic form stage tracking and snapshot management

* fix: standardize string formatting in config coercion and improve logging messages

---------

Co-authored-by: KPC <kpc@kpc.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Junyan Qin <rockchinq@gmail.com>

tests/unit_tests/pipeline/test_config_coercion.py

@@ -0,0 +1,113 @@
+"""Unit tests for config_coercion module"""
+
+from __future__ import annotations
+
+import pytest
+
+from langbot.pkg.pipeline.config_coercion import _coerce_value, coerce_pipeline_config
+
+
+class TestCoerceValue:
+    """Tests for _coerce_value function"""
+
+    def test_none_passthrough(self):
+        assert _coerce_value(None, 'integer') is None
+        assert _coerce_value(None, 'boolean') is None
+
+    def test_string_to_integer(self):
+        assert _coerce_value('120', 'integer') == 120
+        assert _coerce_value('0', 'integer') == 0
+        assert _coerce_value('-5', 'integer') == -5
+
+    def test_integer_passthrough(self):
+        assert _coerce_value(42, 'integer') == 42
+
+    def test_string_to_float(self):
+        assert _coerce_value('3.14', 'number') == 3.14
+        assert _coerce_value('3.14', 'float') == 3.14
+
+    def test_int_to_float(self):
+        assert _coerce_value(3, 'number') == 3.0
+        assert isinstance(_coerce_value(3, 'number'), float)
+
+    def test_float_passthrough(self):
+        assert _coerce_value(3.14, 'float') == 3.14
+
+    def test_string_to_bool(self):
+        assert _coerce_value('true', 'boolean') is True
+        assert _coerce_value('True', 'boolean') is True
+        assert _coerce_value('false', 'boolean') is False
+        assert _coerce_value('False', 'boolean') is False
+
+    def test_bool_passthrough(self):
+        assert _coerce_value(True, 'boolean') is True
+        assert _coerce_value(False, 'boolean') is False
+
+    def test_invalid_bool_string_raises(self):
+        with pytest.raises(ValueError):
+            _coerce_value('notabool', 'boolean')
+
+    def test_unknown_type_passthrough(self):
+        assert _coerce_value('hello', 'string') == 'hello'
+        assert _coerce_value('hello', 'unknown') == 'hello'
+
+    def test_invalid_integer_raises(self):
+        with pytest.raises(ValueError):
+            _coerce_value('abc', 'integer')
+
+
+class TestCoercePipelineConfig:
+    """Tests for coerce_pipeline_config function"""
+
+    def _make_meta(self, section_name: str, stage_name: str, fields: list[dict]) -> dict:
+        return {
+            'name': section_name,
+            'stages': [{'name': stage_name, 'config': fields}],
+        }
+
+    def test_coerce_integer_in_config(self):
+        config = {'trigger': {'misc': {'timeout': '120'}}}
+        meta = self._make_meta('trigger', 'misc', [{'name': 'timeout', 'type': 'integer'}])
+        coerce_pipeline_config(config, meta)
+        assert config['trigger']['misc']['timeout'] == 120
+
+    def test_coerce_boolean_in_config(self):
+        config = {'output': {'misc': {'at-sender': 'true'}}}
+        meta = self._make_meta('output', 'misc', [{'name': 'at-sender', 'type': 'boolean'}])
+        coerce_pipeline_config(config, meta)
+        assert config['output']['misc']['at-sender'] is True
+
+    def test_missing_section_skipped(self):
+        config = {'ai': {}}
+        meta = self._make_meta('trigger', 'misc', [{'name': 'x', 'type': 'integer'}])
+        coerce_pipeline_config(config, meta)  # should not raise
+
+    def test_missing_field_skipped(self):
+        config = {'trigger': {'misc': {}}}
+        meta = self._make_meta('trigger', 'misc', [{'name': 'nonexistent', 'type': 'integer'}])
+        coerce_pipeline_config(config, meta)  # should not raise
+
+    def test_invalid_value_logs_warning(self, caplog):
+        config = {'trigger': {'misc': {'timeout': 'abc'}}}
+        meta = self._make_meta('trigger', 'misc', [{'name': 'timeout', 'type': 'integer'}])
+        import logging
+
+        with caplog.at_level(logging.WARNING):
+            coerce_pipeline_config(config, meta)
+        assert config['trigger']['misc']['timeout'] == 'abc'  # unchanged
+        assert 'Failed to coerce' in caplog.text
+
+    def test_empty_metadata(self):
+        config = {'trigger': {'misc': {'timeout': '120'}}}
+        coerce_pipeline_config(config)  # no metadata args, should not raise
+
+    def test_multiple_metadata(self):
+        config = {
+            'trigger': {'misc': {'timeout': '120'}},
+            'output': {'misc': {'at-sender': 'false'}},
+        }
+        meta_trigger = self._make_meta('trigger', 'misc', [{'name': 'timeout', 'type': 'integer'}])
+        meta_output = self._make_meta('output', 'misc', [{'name': 'at-sender', 'type': 'boolean'}])
+        coerce_pipeline_config(config, meta_trigger, meta_output)
+        assert config['trigger']['misc']['timeout'] == 120
+        assert config['output']['misc']['at-sender'] is False