# Pre12 Batch 05: ZSTD window lower bound

## Change

- Removed only the `rq->em->zstd_windowlog + 10 < 10` subcondition from
  `z_erofs_zstd_decompress`.
- Preserved the `> 20` upper bound, the `outputsize == 0` check, every
  `return (-1)`, all ZSTD calls, resource release, and the complete disabled
  `#else` stub.
- Did not change ZSTD configuration parsing, accepted configuration range,
  conditional compilation, errno behavior, or control flow after the guard.

## Static proof

- `struct erofs_mount.zstd_windowlog` is `uint8_t`, so integer promotion gives
  a value in the range 0 through 255.
- Adding 10 therefore produces a minimum value of 10; comparison with `< 10`
  is unreachable for every representable field value.
- `z_erofs_load_zstd_config` still rejects `windowlog > 10`, so configured
  mount values and the remaining decompression upper-bound behavior are
  unchanged.
- Normalized function comparison confirms that the only removed logical
  tokens are the single unreachable lower-bound subcondition and its `||`.
- `git diff --check` and `git diff --cached --check` completed without errors.

## Tests not run

Per the execution constraints, no build, QEMU run, smoke test, feature test,
or other dynamic test was run. A FreeBSD KLD build with `WITH_ZSTDIO=1`
remains mandatory during final validation so this enabled function body is
compiled.