#2524 STRATA_GR_V3=1 silently falls back to the default read path on gfx1100 (RX 7900 XTX)

说明

On an RX 7900 XTX (gfx1100, Windows, v0.1.44.1), setting `STRATA_GR_V3=1` logs:

```
STRATA_GR_V3=1 needs the two-half split on this card, which fails its checks (#375): the default read is used
```

and the engine continues on the default read path — the variable is a no-op on this card. Measured decode with it set was within run-to-run noise of the control, consistent with the fallback.

Suggestion: document in the GR_V3 description which architectures it applies to, so gfx1100 users don't chase a switch that can't engage. If the two-half split checks are expected to pass on gfx1100, treat this as a bug report instead — happy to provide full logs.