compose_part_from_primitives

        The **CAD-aware generation path** -- instead of asking text-to-mesh AI
        to guess at geometry, describe parts as a tree of primitives combined
        with boolean operations. Produces exact, deterministic, functional parts.

        **SAFETY DEFAULT (changed 2026-04-15):** ``center_on_bed=True`` is the
        default.  OpenSCAD primitives are natively centered on the model origin
        (``cylinder(h,r)`` produces geometry centered on X/Y = (0,0), which
        means half the geometry lives at NEGATIVE X/Y).  Sending such an STL
        to most FDM printers (Bambu, Prusa, Ender, Creality) — whose bed
        origin is the front-left corner — causes the nozzle to drive off-bed
        into the purge/wipe assembly on layer 1.  This happened once on a
        Bambu A1 (incident #0, 2026-04-15, nearly damaged the printer).

        With ``center_on_bed=True`` the output STL is translated so it sits
        centered on the build plate and its lowest point touches z=0.  Set
        ``center_on_bed=False`` only if your downstream flow expects
        origin-centered geometry (e.g. further CAD composition).

        **Operation format** -- each item is either a primitive or boolean:

        Primitive: ``{"type": "primitive", "shape": "<shape>",
        "params": {...}, "translate": [x,y,z], "rotate": [rx,ry,rz]}``

        Boolean: ``{"type": "boolean", "operation": "union|difference|intersection",
        "children": [op1, op2, ...]}``

        **Primitive shapes and params:**
        - cube: ``{"size": [x,y,z]}`` or ``{"size": scalar}``
        - cylinder: ``{"h": height, "r": radius}`` or ``{"h", "r1", "r2"}``
        - sphere: ``{"r": radius}``
        - cone: ``{"h": height, "r1": bottom_r, "r2": top_r}``
        - torus: ``{"major_r": ring_radius, "minor_r": tube_radius}``
        - wedge: ``{"width": w, "depth": d, "height": h}``
        - hex_prism: ``{"r": radius, "h": height}``  -- hexagonal (for nuts)
        - text: ``{"text": "string", "size": 10, "depth": 2}``
        - rounded_cube: ``{"size": [x,y,z], "radius": 1}``
        - pipe: ``{"h": height, "outer_r": 10, "inner_r": 8}``

        Requires OpenSCAD installed on the system.

        :param operations: List of operation dicts (primitive/boolean tree).
        :param output_path: Output path (defaults to temp file).
        :param center_on_bed: Translate output to bed-center (default True).
        :param bed_x_mm: Build plate X dimension for centering (default 256).
        :param bed_y_mm: Build plate Y dimension for centering (default 256).
        :param printer_id: Optional supported printer model id.  When
            provided, printer intelligence supplies the bed size.
        :returns: Dict with result path, SCAD code, triangle count, and
            (if centered) ``bed_centered=True`` + applied translation.