ci: GitHub Actions with a pinned e2fsprogs oracle

Linux + macOS lanes: rustfmt, clippy -D warnings, cargo test (unit +
mke2fs differential), and rustdoc -D warnings. e2fsprogs is built from
the 1.47.4 tag and cached — DESIGN.md's verified claims are against
that exact version, so the oracle must not float with distro
packaging. The loop-mount kernel-oracle lane is reserved for the
writer phase.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: nikhilunni

.github/workflows/ci.yml

@@ -0,0 +1,56 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+env:
+  # The format oracle. DESIGN.md's verified claims are against this exact
+  # version; bumping it is a deliberate oracle upgrade, not routine chore.
+  E2FSPROGS_VERSION: 1.47.4
+
+jobs:
+  test:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-24.04, macos-15]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt, clippy
+
+      - uses: Swatinem/rust-cache@v2
+
+      - name: Cache pinned e2fsprogs
+        uses: actions/cache@v4
+        with:
+          path: ~/e2fsprogs
+          key: e2fsprogs-${{ env.E2FSPROGS_VERSION }}-${{ matrix.os }}
+
+      - name: Build pinned e2fsprogs
+        run: |
+          tools/ci-e2fsprogs.sh "$E2FSPROGS_VERSION" "$HOME/e2fsprogs"
+          echo "E2FSPROGS_SBIN=$HOME/e2fsprogs/sbin" >> "$GITHUB_ENV"
+
+      - name: rustfmt
+        run: cargo fmt --check
+
+      - name: clippy
+        run: cargo clippy --all-targets -- -D warnings
+
+      - name: tests (unit + mke2fs differential)
+        run: cargo test
+
+      - name: docs build cleanly
+        run: cargo doc --no-deps
+        env:
+          RUSTDOCFLAGS: -D warnings
+
+  # Loop-mount kernel-oracle lane lands with the writer (phase 3): it will
+  # mount generated images and diff the tree against the declared
+  # namespace. Kept as a separate job so it can run privileged steps.

README.md

@@ -1,5 +1,7 @@
 # streamext4
 
+[![CI](https://github.com/cortexapps/mke2fs-rs/actions/workflows/ci.yml/badge.svg)](https://github.com/cortexapps/mke2fs-rs/actions/workflows/ci.yml)
+
 Deterministic, streaming, pure-Rust ext4 image builder — plus a
 verification-grade reader. No C dependencies, no kernel mounts, no clocks,
 no RNG.

tools/ci-e2fsprogs.sh

@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+# Build a pinned e2fsprogs into a prefix (idempotent; cache the prefix).
+#
+# The differential tests are oracle-version-sensitive: DESIGN.md's
+# [verified] claims are against e2fsprogs 1.47.4 exactly, so CI must not
+# float with distro/brew packaging.
+#
+# Usage: tools/ci-e2fsprogs.sh <version> <prefix>
+
+set -euo pipefail
+
+VER=$1
+PREFIX=$2
+
+if [ -x "$PREFIX/sbin/mke2fs" ] && "$PREFIX/sbin/mke2fs" -V 2>&1 | head -1 | grep -qF "$VER"; then
+    echo "e2fsprogs $VER already present at $PREFIX (cached)"
+    exit 0
+fi
+
+SRC=$(mktemp -d)
+trap 'rm -rf "$SRC"' EXIT
+
+URL="https://mirrors.edge.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs/v$VER/e2fsprogs-$VER.tar.gz"
+echo "downloading $URL"
+curl -fsSL "$URL" -o "$SRC/e2fsprogs.tar.gz"
+tar -xzf "$SRC/e2fsprogs.tar.gz" -C "$SRC"
+
+cd "$SRC/e2fsprogs-$VER"
+./configure --prefix="$PREFIX" --disable-nls --disable-fuse2fs >/dev/null
+make -j"$(nproc 2>/dev/null || sysctl -n hw.ncpu)" >/dev/null
+make install >/dev/null
+echo "installed e2fsprogs $VER to $PREFIX"
+"$PREFIX/sbin/mke2fs" -V