docs(r17): The Rust toolbox — example 48 + chapter 48 (Appendices: Tooling)

[patterncatalyst]

Rust analog of ch46/ch47 and the final chapter of Part 13. One zero-dependency crate (toolbox, edition 2024, channel 1.97.1) with every gate asserting a real tool-produced effect, never a bare exit code.

The structural point

rustfmt and clippy are rustup components of the pinned channel, so pinning the channel pins the formatter and the linter. That is why ch48's hard core covers formatting and linting offline, where ch47's gofumpt/golangci-lint could only ever be gated-if-present.

Hard gates (A–D) — offline, pinned toolchain only

gate	both directions
A pin + digest	rustup show reports the rust-toolchain.toml override; rustc --version == 1.97.1; toolbox report == 0x481984990deee5ff (byte-identical to ch46 C++ and ch47 Go)
B rustfmt	cargo fmt --check clean on the module tree; rustfmt --check fixtures/misformatted.rs exits 1 with a diff (fixture is outside the module tree, so nothing compiles it)
C clippy	cargo clippy --all-targets -- -D warnings clean by default; --features lintbait fails and names needless_return at src/lintbait.rs:13:5
D cargo test	named digest unit test + test result: ok. 1 passed; 0 failed (not the exit code)

Gated-if-present (E–H)

cargo-nextest, cargo-deny, cargo-llvm-cov, cargo-audit — committed deny.toml/clippy.toml, informational SKIP: when absent, never checks.skip/FAIL. cargo-audit is double-guarded on the binary and on ~/.cargo/advisory-db, so a missing database is a skip rather than a mid-verification network clone.

Deviation from the plan (worth a look)

rust-toolchain.toml components trimmed from ["rustfmt", "clippy", "llvm-tools", "rust-src"] to ["rustfmt", "clippy"]. Pinning llvm-tools made rustup fetch it over the network on the first cargo invocation (info: downloading component llvm-tools), breaking the offline-build claim on a fresh host. Both omitted components are now a documented rustup component add opt-in, covered in the chapter's "What is deliberately not pinned" subsection, and the pipeline diagram was relabelled to match.

Verification (Fedora 44, kernel 7.1.5-201.fc44, offline, no cargo install)

• LSP_LANG=rust lua verify.lua → PASS 20 / FAIL 0, 4 informational SKIPs
• test-all-examples.py --only 48-rust-toolbox → 1 passed, 0 failed, 0 skipped
• validate.py → OK; 15/15 chapter source blocks verbatim; banned-words clean
• all three toolbox binaries (cpp/go/rust) re-run: same digest=0x481984990deee5ff

Details and the full gate matrix in _plans/r17-ch48-plan.md.