compile_scad

        Takes OpenSCAD source code OR a path to a .scad file, compiles
        it using the local OpenSCAD binary, and returns the path to the
        generated STL. Kiln's bundled BOSL2 and MCAD libraries are on
        OpenSCAD's library path (``include <BOSL2/std.scad>``).

        For surface() heightmap operations (photo emboss, lithophane),
        increase timeout to 600+ seconds.

        Kiln checks the compiled part is joined up.  A piece that floats
        with nothing under it is joined to nothing and prints as a loose
        part on supports, or not at all, so the make is REFUSED
        (``code: "FLOATING_PIECES"``; ``error`` names the pieces, how
        far they are from the nearest surface, and the fix): correct
        the geometry and compile again.  Separate parts that all sit on
        the bed are a plate and pass; a piece held inside the part (a
        ball in a cage, a pin in its knuckles) passes with a warning; a
        piece that touches the rest without overlapping it is named in
        ``warnings``.

        A compile where OpenSCAD could not find an included library, an
        imported file or a module is refused too: OpenSCAD leaves that
        part out and still exits cleanly, so the file would be missing
        pieces.  ``error`` names what was missing.

        Colour: pass ``color`` (a name such as ``"teal"`` or a hex) when
        the user asked for one, and the preview and the 3D stage show
        the part in it.  Left out, a single ``color("...")`` in the
        source is used.  It is how the part is SHOWN; it prints in
        whatever filament is loaded, and the result's ``color`` block
        says so.

        Round shapes: leave ``$fn`` out and Kiln cuts each curve by its
        size, writing that rule into the file it compiles.  Set ``$fn``
        only for a deliberate polygon (``$fn = 6`` for a hexagon).  A
        file that sets ``$fn``, ``$fa`` or ``$fs`` at the top compiles
        exactly as written, and the result's ``curve_resolution`` note
        says so.

        Named parts: a source may define each part as its own module and
        compose them in ``module main()``, drawing nothing at the top
        level; it compiles to ``main()``.  Kiln keeps generated designs
        this way, so a kept source compiles as it is.

        When you pass ``fastener``, the result carries a
        ``fastener_advice`` block saying the code compiled as written
        and nothing resized the hole for that fastener.  Kiln raises
        it once per session across every tool that can raise it.  Read
        its ``agent_instruction`` before repeating any of it.

        Args:
            brief_id: The saved goal's id from ``design_session``, so this make
                is recorded against the goal and checked against it. Empty when
                there is no goal.
            scad_code: Valid OpenSCAD source code (provide this OR scad_path).
            scad_path: Path to a .scad file (provide this OR scad_code).
            timeout: Maximum compilation time in seconds (default 300).
            fastener: The fastener the user named, e.g. ``"M4"`` — pass
                only if they actually said one.  Kiln does NOT read your
                OpenSCAD looking for screw holes; guessing intent out of
                geometry would be wrong often. No argument, no advisory.
            color: The colour the user asked for, shown on the preview and
                the stage (a name or ``#rrggbb``).  Not a print setting.