rust-1.90.0 prerelease tries to download rust-std in offline mode

hey everyone,

I've just downloaded the rust-1.90.0 prerelease tarball, and tried to compile it. It didn't work, because something tries to download a rust-std:

>>> Compiling source in /var/tmp/portage/dev-lang/rust-1.90.0/work/rustc-1.90.0-src ...
downloading https://static.rust-lang.org/dist/2025-08-07/rust-std-1.89.0-x86_64-unknown-linux-gnu.tar.xz
running: curl --progress-bar --retry-all-errors --location --speed-time 30 --speed-limit 10 --connect-timeout 30 --output /var/tmp/portage/dev-lang/rust-1.90.0/temp/tmp1ribmlnu --continue-at - --retry 3 --show-error --remote-time --fail https://static.rust-lang.org/dist/2025-08-07/rust-std-1.89.0-x86_64-unknown-linux-gnu.tar.xz
curl: (6) Could not resolve host: static.rust-lang.org
Warning: Problem : timeout. Will retry in 1 second. 3 retries left.

this can't work, because I'm building in a sandbox via emerge*, which doesn't allow any online fetching of external sources. (emerge is gentoo's package manager)

this command is used:

RUST_BACKTRACE=1 python3.13 ./x.py build -vvv --config=/var/tmp/portage/dev-lang/rust-1.90.0/work/rustc-1.90.0-src/bootstrap.toml -j12

[llvm]
llvm.download-ci-llvm = false
llvm.optimize = true
llvm.release-debuginfo = false
llvm.assertions = false
llvm.ninja = true
llvm.targets = "AArch64;X86;ARM;WebAssembly"
llvm.experimental-targets = ""
llvm.link-shared = false


llvm.enable-warnings = false
[llvm.build-config]
CMAKE_VERBOSE_MAKEFILE = "ON"
CMAKE_C_FLAGS_RELEASE = "-O2 -march=znver1 -pipe"
CMAKE_CXX_FLAGS_RELEASE = "-O2 -march=znver1 -pipe"
CMAKE_EXE_LINKER_FLAGS_RELEASE = "-Wl,-O1 -Wl,--as-needed -Wl,-z,pack-relative-relocs"
CMAKE_MODULE_LINKER_FLAGS_RELEASE = "-Wl,-O1 -Wl,--as-needed -Wl,-z,pack-relative-relocs"
CMAKE_SHARED_LINKER_FLAGS_RELEASE = "-Wl,-O1 -Wl,--as-needed -Wl,-z,pack-relative-relocs"
CMAKE_STATIC_LINKER_FLAGS_RELEASE = ""
[build]
build.build-stage = 2
build.test-stage = 2
build.build = "x86_64-unknown-linux-gnu"
build.host = ["x86_64-unknown-linux-gnu"]
build.target = ["x86_64-unknown-linux-gnu"]
build.cargo = "/var/tmp/portage/dev-lang/rust-1.90.0/work/rust-stage0/bin/cargo"
build.rustc = "/var/tmp/portage/dev-lang/rust-1.90.0/work/rust-stage0/bin/rustc"
build.rustfmt = "/var/tmp/portage/dev-lang/rust-1.90.0/work/rust-stage0/bin/rustfmt"
build.docs = false
build.compiler-docs = false
build.submodules = false
build.python = "python3.13"
build.locked-deps = true
build.vendor = true
build.extended = true
build.tools = ["cargo","rustdoc","rustfmt"]
build.verbose = 2
build.sanitizers = false
build.profiler = true
build.cargo-native-static = false
[install]
install.prefix = "/usr/lib/rust/1.90.0"
install.sysconfdir = "etc"
install.docdir = "share/doc/rust"
install.bindir = "bin"
install.libdir = "lib"
install.mandir = "share/man"
[rust]
# https://github.com/rust-lang/rust/issues/54872
rust.codegen-units-std = 1
rust.optimize = true
rust.debug = false
rust.debug-assertions = false
rust.debug-assertions-std = false
rust.debuginfo-level = 0
rust.debuginfo-level-rustc = 0
rust.debuginfo-level-std = 0
rust.debuginfo-level-tools = 0
rust.debuginfo-level-tests = 0
rust.backtrace = true
rust.incremental = false
rust.default-linker = "x86_64-pc-linux-gnu-gcc"
rust.channel = "stable"
build.description = "gentoo"
rust.rpath = false
rust.verbose-tests = true
rust.optimize-tests = true
rust.codegen-tests = true
rust.dist-src = false
rust.remap-debuginfo = true
rust.lld = false
# only deny warnings if doc+wasm are NOT requested, documenting stage0 wasm std fails without it
# https://github.com/rust-lang/rust/issues/74976
# https://github.com/rust-lang/rust/issues/76526
rust.deny-warnings = true
rust.backtrace-on-ice = true
rust.jemalloc = false
# See https://github.com/rust-lang/rust/issues/121124
rust.lto = "off"
[dist]
dist.src-tarball = false
dist.compression-formats = ["xz"]
dist.compression-profile = "balanced"
[target.x86_64-unknown-linux-gnu]
ar = "x86_64-pc-linux-gnu-ar"
cc = "x86_64-pc-linux-gnu-gcc"
cxx = "x86_64-pc-linux-gnu-g++"
linker = "x86_64-pc-linux-gnu-gcc"
ranlib = "x86_64-pc-linux-gnu-ranlib"
rust.llvm-libunwind = "no"

my OS is gentoo linux 64bit

the git-commit-hash is 1159e78c4747b02ef996e55082b704c09b970588

Reproduce the offline build with ./x.py build and the provided bootstrap.toml, using the reported commit and verbose output. Trace which bootstrap stage requests rust-std-1.89.0 and check how the build configuration supplies its dependencies. Done means the reported build completes without attempting an external download.