feat: add export_gencad tool (kicad-cli, GenCAD assembly/test format)

New MCP tool `export_gencad` wrapping `kicad-cli pcb export gencad`:
exposes define-var plus the flip-bottom-pads, unique-pins,
unique-footprints, use-drill-origin and store-origin-coord flags.
Self-contained interface handler reading the saved .kicad_pcb.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

python/kicad_interface.py

@@ -592,6 +592,7 @@ class KiCADInterface:
             "export_ipc2581": self._handle_export_ipc2581,
             "export_odb": self._handle_export_odb,
             "export_ipcd356": self._handle_export_ipcd356,
+            "export_gencad": self._handle_export_gencad,
             "generate_netlist": self._handle_generate_netlist,
             "sync_schematic_to_board": self._handle_sync_schematic_to_board,
             "list_schematic_libraries": self._handle_list_schematic_libraries,
@@ -4888,6 +4889,76 @@ class KiCADInterface:
             logger.error(f"Error exporting IPC-D-356: {e}")
             return {"success": False, "message": str(e)}
 
+    def _handle_export_gencad(self, params: Dict[str, Any]) -> Dict[str, Any]:
+        """Export the PCB in GenCAD format via kicad-cli (`pcb export gencad`).
+
+        GenCAD is an assembly/test interchange format. Exposes the padstack-flip,
+        unique-pin/footprint, drill-origin, and store-origin flags. Reads the
+        saved .kicad_pcb.
+        """
+        import subprocess
+
+        logger.info("Exporting GenCAD via kicad-cli")
+        try:
+            board_path = params.get("boardPath") or self._current_board_path()
+            output_path = params.get("outputPath")
+
+            if not board_path:
+                return {
+                    "success": False,
+                    "message": "boardPath is required (no current board could be resolved)",
+                }
+            if not os.path.exists(board_path):
+                return {"success": False, "message": f"Board not found: {board_path}"}
+            if not output_path:
+                return {"success": False, "message": "outputPath is required"}
+
+            kicad_cli = self._find_kicad_cli_static()
+            if not kicad_cli:
+                return {"success": False, "message": "kicad-cli not found in PATH"}
+
+            output_path = os.path.abspath(os.path.expanduser(output_path))
+            parent = os.path.dirname(output_path)
+            if parent:
+                os.makedirs(parent, exist_ok=True)
+
+            cmd = [kicad_cli, "pcb", "export", "gencad", "--output", output_path]
+
+            for kv in params.get("defineVar", []) or []:
+                cmd += ["--define-var", kv]
+
+            flag_map = {
+                "flipBottomPads": "--flip-bottom-pads",
+                "uniquePins": "--unique-pins",
+                "uniqueFootprints": "--unique-footprints",
+                "useDrillOrigin": "--use-drill-origin",
+                "storeOriginCoord": "--store-origin-coord",
+            }
+            for key, flag in flag_map.items():
+                if params.get(key):
+                    cmd.append(flag)
+
+            cmd.append(board_path)
+
+            logger.info(f"Running: {' '.join(cmd)}")
+            result = subprocess.run(cmd, capture_output=True, text=True, timeout=180)
+
+            if result.returncode != 0:
+                return {
+                    "success": False,
+                    "message": f"kicad-cli failed (exit {result.returncode}): "
+                    f"{result.stderr.strip()}",
+                }
+            return {"success": True, "outputPath": output_path}
+
+        except FileNotFoundError:
+            return {"success": False, "message": "kicad-cli not found in PATH"}
+        except subprocess.TimeoutExpired:
+            return {"success": False, "message": "kicad-cli timed out after 180 seconds"}
+        except Exception as e:
+            logger.error(f"Error exporting GenCAD: {e}")
+            return {"success": False, "message": str(e)}
+
     def _handle_generate_netlist(self, params: Dict[str, Any]) -> Dict[str, Any]:
         """Generate netlist from schematic and return structured JSON.