fix(init): pre-commit hook runs cargo fmt --check on staged Rust (REQ-210, #438)

[avrabe]

Problem (#438)

rivet init --hooks installs a pre-commit hook that runs only rivet validate — there is no formatting gate. A misformatted-Rust diff is the single most common first-push CI failure, and AI agents kept hitting it: the commit "passes" locally (validate is clean), then CI's cargo fmt --check job goes red.

The fmt-checking pre-commit hook that this repo actually uses was installed by the dev-only scripts/install-hooks.sh — which rivet init --hooks does not use. So every project that adopts hooks the shipped way gets no formatting gate. (The original issue framed it as the Claude Code hook missing fmt; the accurate root cause is the shipped cmd_init_hooks template.)

Fix

cmd_init_hooks (rivet-cli/src/main.rs) now writes a pre-commit hook that runs cargo fmt --all -- --check before the existing rivet validate step — guarded to stay language-agnostic:

if command -v cargo >/dev/null 2>&1 \
    && git diff --cached --name-only --diff-filter=ACM | grep -q '\.rs$'; then
    if ! cargo fmt --all -- --check; then
        echo "cargo fmt: formatting issues. Run 'cargo fmt --all', then re-stage."
        exit 1
    fi
fi

The fmt step runs only when cargo is on PATH and the commit stages at least one .rs file, so non-Rust rivet projects (and cargo-less machines) skip it silently and are never blocked. Mirrors the proven logic in scripts/install-hooks.sh. Convenience only — CI remains the real gate (REQ-051) and --no-verify still bypasses it.

Verification (acceptance, REQ-210)

• Temp-repo rivet init --hooks → generated .git/hooks/pre-commit contains the fmt step + the .rs guard + the command -v cargo guard, preserves the rivet validate --format json step, and passes bash -n.
• cargo test -p rivet-cli --test cli_commands — 127 passed, 0 failed (the full CLI suite, per the REQ-209 lesson).
• cargo fmt --check + cargo clippy -p rivet-cli --all-targets -- -D warnings — exit 0.
• rivet validate — PASS.

REQ-210 filed and flipped to implemented in the same commit (repo convention, cf. REQ-208).

Closes #438.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[github-actions]

📐 Rivet artifact delta

Change	Count
Added	1
Removed	0
Modified	0
Downstream impacted (depth ≤ 5)	0

Graph

graph LR
  REQ_210["REQ-210"]:::added
  classDef added fill:#d4edda,stroke:#28a745,color:#155724
  classDef removed fill:#f8d7da,stroke:#dc3545,color:#721c24
  classDef modified fill:#fff3cd,stroke:#ffc107,color:#856404
  classDef overflow fill:#e2e3e5,stroke:#6c757d,color:#495057,stroke-dasharray: 3 3

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Added

• REQ-210

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