diag(track-a): test DRI path with default Xvfb GLX state

[blakinio]

Track A RUNTIME-INFRA — final Xvfb DRI-path minimality discriminator

Task: OTC-20260816-track-a-xvfb-dri-path-default-glx.
Base: exact trusted main@d3f186414256151c9d5e03f34c5a9026b1fba500.
Execution: exactly one governance-compliant ephemeral_isolated Xvfb-only workflow on synology-otclient-01.

Draft #420 proved the contained DRI provider path enables GLX when +extension GLX is also present. The current canonical worker has neither setting. This task resolves the final minimality question by preserving the worker's current Xvfb arguments exactly and adding only:
LIBGL_DRIVERS_PATH=/work/_otclient_tibia_re_state/toolroot/usr/lib/x86_64-linux-gnu/dri.

No +extension GLX, client, VNC, WARP, canonical lease/registration/session, credentials, login, gameplay, Track B or historical #303 surface is used. Other provider overrides are explicitly unset.

If GLX appears, the hosted worker fix needs only the environment variable. If it remains absent, the fix needs both the DRI path and explicit extension enablement. Exactly one valid semantic run is allowed.

Research output remains Draft-only; coordinator promotion is separate.

[blakinio]

Coordinator disposition: ACCEPT / CLOSED_SUPERSEDED_BY_427. Independent review of semantic job 95210624747 confirms the canonical-shaped contained Xvfb started without +extension GLX, with only contained LIBGL_DRIVERS_PATH added, advertised GLX with opcode 150, preserved RENDER, started no official client/VNC/WARP, touched no canonical state, and cleaned up. Final source head a359ab908772e95e1dbae850f6ef4de1738cbf05 also passed Track A governance 31965851223 and CI 31965851220 / CI / Required 95210823079. Accepted task/evidence were replayed from current main into #427; this source Draft is closed unmerged to avoid stale branch history.