fix(export): force vis=False so export runs headless

[KraHsu]

Problem

genelab export <trainable-task> <ckpt> -f torchscript|onnx crashes on any
display-less machine (CI / remote server) with:

genesis.GenesisException: No display detected. Use `show_viewer=False` for headless mode.

and there's no CLI override to disable the viewer (No such option: --env.simulation.vis).

Root cause

export_task (src/genelab/cli/_export.py) resolves the play env via
resolve_env_cfg(task_id, play=True). Trainable tasks set simulation.vis=play
(e.g. examples/inverted_pendulum/.../env_cfg.py), so the play env has the
viewer on. interactive_scene.py:198 wires show_viewer=self._sim_cfg.vis, so
building that env on a machine with no display raises. Export only probes obs
shapes — it never renders — so it must force the viewer off, exactly as
eval_task already does (eval_task.py:74, "eval is always headless").

Fix

Set env_cfg.simulation.vis = False right after resolving the env cfg in
export_task. The episode_length_s > 30 clamp eval_task applies is not
needed here — export collects no episodes (verified).

Test

Adds tests/test_export.py::test_export_task_forces_headless_vis: drives the
real export_task with env resolution/build monkeypatched out (no Genesis
runtime, no display), starting from a fake play env cfg with vis=True, and
asserts (a) the cfg handed to build_env has vis is False and (b) the real
exporter produces the .ts + .metadata.json.

tests/test_export.py — 7 passed; ruff clean + formatted.

Reference audit

find_referencing_symbols(export_task) → only caller is
src/genelab/cli/__init__.py::export_cmd (line 394/397). The change adds a line
inside the function body; no symbol renamed/removed, no caller affected.

Verification gap (please confirm on H100/H200)

This change targets the exact vis -> show_viewer knob and mirrors the proven
eval_task approach. I could not fully reproduce the original crash on the
dev box because it has libEGL + offscreen Qt (env build succeeds even with
vis=True). A real genelab export run got past env build headless, then
failed on an unrelated rsl_rl did not expose an actor module (the local
inverted-pendulum checkpoints look like smoke artifacts) — so no green .ts was
produced end-to-end locally. Please run, with a good checkpoint:

QD_GRAPH=0 QT_QPA_PLATFORM=offscreen genelab export GeneLab-Inverted-Pendulum-v0 <ckpt> -f torchscript --out /tmp/p.ts

🤖 Generated with Claude Code