Every answer comes from the deterministic RotoSpider geometric layout
    engine: rotation-envelope and dead-height checks, pairwise mold-to-mold
    clearance, offset-arm riser selection, and ring arrangements for 3+
    identical molds. It never returns a physically invalid layout.

    Args:
        molds: List of mold objects. Use one explicit unit convention:
            Box/frame mold: {"length_mm": L, "width_mm": W, "height_mm": H}.
            Cylinder/tank mold: {"diameter_mm": D, "height_mm": H}.
            Exact L, slope, triangle, frustum, or complex mold: measured
            length_mm+width_mm+height_mm plus the complete
            geometry_asset_id+geometry_asset_revision returned by the
            geometry WebAPI or another trusted publisher.
            Decimal-inch aliases are length_in, width_in, height_in, and
            diameter_in. Each value is converted once to canonical
            micrometres; do not give both aliases for the same value.
            Optional per mold: "name", "weight_kg", "quantity" (default 1;
            use 0 to retain the mold type without requesting a copy).
        machine: Public-sample straight-arm preset. Available models are
            listed in the tool description. Leave empty AND give no
            explicit geometry to scan all presets ("which machine can take
            these molds?").
        arm_type: 'straight' (dual spiders) or 'offset' (single-spider
            offset/L arm). Empty = both.
        spider_diameter_mm: Custom machine - spider (mounting plate)
            diameter. Giving this plus envelope_diameter_mm switches to
            custom-machine mode instead of presets.
        envelope_diameter_mm: Custom machine - rotation envelope diameter
            (for offset arms: the vertical envelope diameter).
        dead_height_mm: Custom straight arm - unusable center height
            between the upper and lower spider surfaces.
        offset_spider_y_mm: Custom offset arm - spider Y offset from the
            spider center to the sphere center (required for custom offset).
        offset_horz_diameter_mm: Custom offset arm - horizontal usable
            envelope diameter after side trim (defaults to envelope).
        riser_heights_mm: Custom offset arm - available riser heights; the
            solver picks the best (or none).
        *_in: Decimal-inch aliases for the matching custom-arm and
            clearance *_mm arguments.
        max_load_weight_kg: Optional arm weight capacity; the solver loads
            molds only up to this total weight.
        clearance_target_mm: Target mold-to-mold clearance (default 300).
        clearance_min_mm: Minimum acceptable clearance (default 150).
        allow_overhang_within_envelope: Allow every mold shape to extend
            past the spider edge while its complete active shape remains
            inside the rotation envelope. Defaults to false.
        include_layout: Include request-relative mold placements. Use with
            response_api v1/v2/v3 to select the placement heading dialect.
        display_unit: 'mm' (default) or 'in'. Canonical result fields remain
            millimetres; 'in' adds a display projection rounded to 0.00001 in.
        response_api: Public placement dialect. Defaults to
            rotospider.layout-check.v1; request rotospider.layout-check.v2
            for exact four-heading orient keys when layouts are included.

    Returns a summary sentence plus per-arm results: feasible, placed vs
    requested counts (per mold type when available), selected riser height,
    spider utilization, center-of-gravity offset, achieved clearance, and
    the engine's reason when molds do not fit.