id: toolchain title: The build is cheap enough to run two of status: shipped repos: [atgc] dependsOn: [] exitCriterion: > A fresh worktree builds on a pinned toolchain, with the language floor enforced on every build rather than asserted once. #

toolchain #

rust-version = "1.89" is set by three things independently, and declaring it turns clippy's incompatible_msrv on, so the floor is enforced rather than believed. Dependencies build without debug info and this crate keeps all of it, which took a full debug build from 2.43 GiB to 1.66 with 253 dependency source files still carrying line tables.

One target/ per worktree, cargo's default, and no scheme on top of it. Sharing the build across worktrees was tried twice and is settled as a no: the uplifted target/debug/atgc is one name written by whichever worktree last compiled, and it is what env!("CARGO_BIN_EXE_atgc") bakes into the integration tests.

What it needs #

• Every fresh worktree pays one >4 GiB compile, and it is not the debug info. [patch.crates-io] jacquard-oauth = { path = "vendor/…" } puts an absolute path into the metadata hash, so jacquard-oauth and everything downstream of it — jacquard-api above all — is rebuilt from cold in every new worktree, however warm the main checkout's target dir is. Measured while capping builds in a cgroup: a single rustc on jacquard-api will not complete under a 4 GiB ceiling even at -j1 with the machine otherwise idle, while atgc's own units peak around 1.5-1.8 GiB. That is worth knowing before running two agents at once on a 30 GiB laptop, and it is not an argument for a shared target directory — that was reversed deliberately in 0a8a56e and would trade a known cost for a known bug. Left recorded rather than fixed: the patch is what pins the three vendored fixes, and dropping it is the same work as landing them upstream

Done #

• prek hooks over file hygiene, cargo fmt --check and clippy -D warnings, on the pinned toolchain (prek.toml, rust-toolchain.toml)
• rust-version = "1.89" in Cargo.toml. Three things set that floor independently: edition 2024's let-chains want 1.88, File::try_lock and TryLockError (src/config/lock.rs) stabilised in 1.89, and smol_str 0.3.6 — the highest rust-version in the resolved graph, arriving under jacquard — declares 1.89 itself. Declaring it also turns clippy's incompatible_msrv on, so the floor is now enforced on every build rather than asserted once; dropping the key to 1.88 reports try_lock and nothing else, which is how the number was established. Not rust-toolchain.toml's 1.97.1, which is what it is built with here and moves on its own schedule
• One target/ per worktree, cargo's default, and no scheme on top of it. Sharing the build across worktrees was tried twice and is settled as a no: the uplifted target/debug/atgc is one name written by whichever worktree last compiled, and it is what env!("CARGO_BIN_EXE_atgc") bakes into the integration tests — once a green test run against another branch's binary
• Dependencies build without debug info, this crate keeps all of it — [profile.dev.package."*"] debug = false, whose "*" reaches every dependency and no workspace member. Measured on a full debug build: 2.43 GiB to 1.66 GiB, target/debug/deps 1.93 to 1.31, the binary 228 to 102 MB and its .debug_info 70 MiB to 27, and the build itself a little quicker. Cheaper in debuggability than it looks, because a dependency's generic code is monomorphized into atgc's codegen units and keeps atgc's settings: 253 dependency source files still have line tables in the result. Only separately compiled non-generic dependency code loses file and line, and symbol names survive regardless