ObjectGallery --render <name>   : add one object, route its texture output to
                                  an offscreen window, play, and exit 0 if it
                                  rendered a full run without crashing (a
                                  render-path crash kills the process, which
                                  the driver attributes to that object).
render-sweep.sh [filter]        : run --render for each object on BOTH GL
                                  backends (llvmpipe and the machine's GPU via
                                  X11) and tally crashes.

Texture objects (ISF, images, model display, ...) render clean on both
backends. Two follow-ups: geometry-only objects need a display chain (they
currently abort when run standalone), and the offscreen readback does not yet
composite the routed texture so the non-blank check is informational.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014rZgzE8JjWvHDtaVUhxpLE

ObjectGallery gains a --shader <file> mode: it loads a shader tester
(.fs/.frag/.glsl as an ISF Shader, .cs/.comp/.csf as a Compute Shader) into a
process, routes its texture output to an offscreen window and renders it,
exiting non-zero if it fails to compile or crashes.

csf-sweep.sh drives that over the csf-examples corpus on BOTH GL backends
(llvmpipe and the machine's GPU via X11). On the csf-testers set, 100/121
shaders render on both backends; the remaining 21 are geometry-producing
compute shaders that need a downstream raster stage to display (see the
corpus's tests.txt) — chaining them is the next step.

Also fixes the sweep drivers to pass per-backend env via `env`, since bash
does not treat VAR=val from an expanded "$@" as assignments.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014rZgzE8JjWvHDtaVUhxpLE

test_unit_threedim_loaders: AssetLoader/GltfParser/FbxParser/TinyObj/Ply/Vcg
+ the PrimitiveCloud parsers, compiled straight into the test (plugin is
-fvisibility=hidden). test_unit_primitivecloud: PLY/.splat/.spz parsers +
scene helpers. ObjectGallery: explicit llvm profile flush on _Exit +
SEGV/ABRT so coverage runs of the render-regression harness still emit
.profraw (atop this branch's render-regression mode).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014rZgzE8JjWvHDtaVUhxpLE