Bring the workspace back to rustfmt, and keep it there

[JamesKane]

cargo fmt --all had drifted far enough that running it touches 116 files. That made it a tax on every feature branch: either carry a pile of unrelated reformatting into review, or de-noise the diff by hand before opening the PR (which is what #43 had to do). Two commits — clear the drift, then stop it coming back.

main is genuinely drifted, not misconfigured — stable rustfmt disagrees with main too, so this isn't a nightly-toolchain artifact.

1. 7c4fbf6 — the reformat

Almost all mechanical cargo fmt --all output, skimmable. There are two places I did not simply take what the tool produced, and those are the only spots worth a real look:

20 hand-inserted blank lines, across 13 files. Where a standalone comment block directly follows a line that already ends in a trailing comment, rustfmt aligns the block to that comment's column — pushing text out to column 50–90 and, in a few cases, past the 120 the config asks for:

let _ = tx.send(Command::LoadAssetStatus); // ancestry/IBD "data sources" line
                                           // Check for a newer installer at startup (unless the user opted out). Non-fatal — a failed
                                           // check just logs to the status line; the app never auto-updates.

That is worse than the drift it replaces, so a blank line breaks the association and the comments sit at their natural indent. Two of these artifacts already existed on main (ui/mod.rs, domain/src/consensus.rs) — fixed here too.

One comment rewritten — navigator-analysis/src/archaic.rs. The // 400 absent entirely note documented a panel site deliberately missing from the genotype list, and rustfmt could only render it at a bad indent inside the vec![]. It is now a sentence above the binding. This is the only content change in the branch.

2. 2534c37 — the hook

.githooks/pre-commit runs cargo fmt --all --check and rejects a commit that would reintroduce drift. Local, not CI — the useful moment to catch this is before it is committed, not after a build fails. ~0.6s, compiles nothing, so there is no incentive to disable it.

It only ever checks; it never reformats your tree mid-commit, because a commit whose contents you did not read is a worse failure than the one being prevented. It reports the offending files and the fix.

Stays out of the way where it has no business: no cargo on PATH exits 0, and so does a commit with no staged .rs files — which also covers merges and reverts. --no-verify is the escape hatch.

Enable once per clone (hooks are per-clone git config, so this is not automatic on checkout — CLAUDE.md documents it):

git config core.hooksPath .githooks

Testing

cargo fmt --all --check clean and idempotent · cargo clippy --all-targets clean · cargo test --workspace green, 0 failures.

Hook exercised on both paths: clean tree passes, staged drift is rejected with the file list, and the rejected commit is genuinely not created. The no-staged-.rs path is exercised by 2534c37 itself, which the hook correctly let through.

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