refactor: convert PipelineResult from dataclass to Pydantic BaseModel

- Replace @dataclass with Pydantic BaseModel
- Add model_config with arbitrary_types_allowed for ExecutionResult.cq.Workplane
- Change exported_files default to Field(default_factory=dict)
- Add TestPipelineResultModel with model_dump and default_exported_files tests
- All 9 tests pass

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/pipeline.py

@@ -9,10 +9,11 @@ Pipeline stages:
   5. (Optional) Auto-retry with error feedback if execution fails
 """
 
-from dataclasses import dataclass
 from pathlib import Path
 from typing import Optional
 
+from pydantic import BaseModel, Field
+
 from core.cadquery_prompts import build_messages
 from core.executor import ExecutionResult, execute_cadquery, export_all
 from core.validator import validate_for_cnc, CNCValidationResult
@@ -25,13 +26,14 @@ from core.backends import (
 # ── Pipeline ──────────────────────────────────────────────────────────────
 
 
-@dataclass
-class PipelineResult:
+class PipelineResult(BaseModel):
+    model_config = {"arbitrary_types_allowed": True}
+
     prompt: str
     generated_code: str
     execution: ExecutionResult
     validation: Optional[CNCValidationResult] = None
-    exported_files: dict[str, Path] = None
+    exported_files: dict[str, Path] = Field(default_factory=dict)
     retry_count: int = 0
 
     def summary(self) -> str:

tests/test_pipeline.py

@@ -7,6 +7,7 @@ import pytest
 from pathlib import Path
 from core.pipeline import run_pipeline, PipelineResult
 from core.backends import MockBackend
+from core.executor import ExecutionResult
 
 pytestmark = pytest.mark.requires_cadquery
 
@@ -76,3 +77,23 @@ class TestRunPipeline:
             output_dir=tmp_output_dir,
         )
         assert result.execution.success is True
+
+
+class TestPipelineResultModel:
+    def test_model_dump(self):
+        exec_result = ExecutionResult(success=True, volume=1000.0, bounding_box=(10, 10, 10), face_count=6, edge_count=12)
+        pr = PipelineResult(
+            prompt="test",
+            generated_code="code",
+            execution=exec_result,
+            retry_count=0,
+        )
+        d = pr.model_dump()
+        assert d["prompt"] == "test"
+        assert d["retry_count"] == 0
+
+    def test_default_exported_files(self):
+        exec_result = ExecutionResult(success=False, error="fail")
+        pr = PipelineResult(prompt="test", generated_code="code", execution=exec_result)
+        assert pr.exported_files == {}
+        assert pr.validation is None