[PR #26] Missing rust-toolchain.toml — builds not pinned to specific toolchain

[obchain]

PR: #26 (feat/01-scaffold-workspace)
Commit: cb1a5eb
File: repository root (file absent)

Problem: No rust-toolchain.toml committed. Workspace declares edition = "2024", requires Rust 1.85+. Cargo.lock uses v4 format (1.78+). Without pinned toolchain, contributors / CI runners on older stable get cryptic errors. Hetzner Docker build stack and local dev silently diverge if host toolchains differ.

Impact: Reproducibility breaks across dev machines, CI, Docker. Workspace foundation PR is the place to pin.

Fix: Add rust-toolchain.toml at repo root:

[toolchain]
channel = "1.85.0"
components = ["rustfmt", "clippy"]

Pin to exact stable version, not floating stable.

[obchain]

Fixed on feat/01-scaffold-workspace in 760c168.