id reports uid=0(root) gid=0(root) groups=0(root). The world has one user. -u and -g print zero. -n prints root, including -un and -gn.
du sums apparent file sizes. Directories contribute zero bytes. It supports -s, -h, -a, -c, -d/--max-depth, -b, and -k. The default unit and -k use 1024 bytes. -b uses bytes. Symlinks contribute their own size. The command does not follow them. Native comparisons use du --apparent-size on files. Native directory totals include host directory storage, which the world does not expose.
stat supports -c/--format, -L, and multiple paths. Formats: %n %s %F %Y %y %X %x %N %% %a %A %U %G %u %g. Times use UTC. UID and GID are zero. User and group names are root. Modes are fixed at 755 for directories and 644 otherwise. The default output prints names, sizes, types, modes, identity, and timestamps.
nohup COMMAND [ARG...] uses the existing process interface. It starts an independent process group and returns the command's exit status. The world has no terminal or SIGHUP. Non-terminal streams remain inherited. It does not detach the command or create nohup.out, like native nohup with redirected streams.

Tests

From userland/, use the executor's CARGO_TARGET_DIR:

nix develop -c cargo build -p sausage-fs-tools --release --locked
nix develop -c nu --no-config-file fs-tools/test.nu
nix develop -c nu --no-config-file fs-tools/world-test.nu /tmp/s6-esbuild/app /tmp/s6-esbuild/esbuild-native

The world test requires the host binary and brush in the same target folder. It also requires the pinned preview1 tools and the built archive tools. The fixture contains S6's app, check.mjs, and its installed dependencies. The test creates a fresh world under /tmp. It does not use the live world.