[bmachek]

What broke

The v3.7.0 release failed on every build that compiles llama.cpp as shared libraries: Windows x64, Docker vulkan x64 and Docker cuda x64 (run 43443281904). All three panic in the same place:

llama-cpp-sys-2-0.1.156/build.rs:1431:56:
called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, ... }

Why

Rust 1.100.0 (released 2026-11-12, picked up through stable / rust:1-trixie) stabilised Cargo's new build-dir layout: build-script output moved from build/<crate>-<hash>/out to build/<crate>/<hash>/out. llama-cpp-sys-2's get_cargo_target_dir() walks a fixed three levels up from OUT_DIR, so it now lands on target/release/build and panics hard-linking its shared libs into target/release/build/deps, which does not exist. Only dynamic-backends/shared-lib builds take that path, which is why vulkan aarch64 (statically linked) passed. v3.6.0 built on 1.99 with the same pinned 0.1.156.

• Upgrading does not help: the latest llama-cpp-sys-2 (0.1.161) has the same code.
• Cargo has no switch back to the old layout.
• Our own packaging assumes the old layout too: the Dockerfile globs build/llama-cpp-sys-2-*/out/{lib,lib64,backends}, and release.yml takes llama.dll/ggml*.dll from target/release, where build.rs used to link them.

Change

Hold the toolchain at 1.99 for these builds, with the reason and the unpin checklist next to each pin:

• server-rs/Dockerfile: ARG RUST_VERSION=1.99, used by the shared rust:${RUST_VERSION}-trixie stage.
• release.yml: rust_toolchain per matrix leg ('1.99' for Windows, stable for macOS). Also names components: clippy, because the action installs with --profile minimal and a pinned version is a fresh install.
• Dev-Build-Environment-Setup.md: Windows llamacpp builds use cargo +1.99, since local builds hit the same panic.
• server-rs/README.md (and its generated wiki page): builder image named.

Trade-off: PR CI stays on stable, so code that needs Rust 1.100 would pass PR checks and only fail on the Windows release leg. The workspace builds on 1.99.1 today.

Testing

• check-docs.py and the pre-commit hooks pass; release.yml parses with the intended matrix values.
• This PR triggers docker-images.yml (Dockerfile changed), which builds the vulkan/cuda x64 images on 1.99.
• The Windows leg only runs from release.yml; v3.7.1 will exercise it.

Docs-Reviewed: Help-Docker-GPU.md (still accurate; the toolchain is not a build arg users set)

🤖 Generated with Claude Code

https://claude.ai/code/session_01HaMMvthhWBNXkrgY4AzYiH