Add bin/test --build-only, which runs the test build and stops

AGENTS.md

@@ -40,6 +40,7 @@ BAD: `cargo check --package liboxen`
 ```bash
 cargo build --workspace                           # Debug build
 cargo build --workspace --bins --tests            # Debug build that a later `cargo test` reuses
+bin/test --build-only                             # The build bin/test runs, without the tests
 ```
 
 A `cargo build` that a `cargo test` follows, in a script or a CI job, builds `--bins --tests` with the same packages and features the test command selects, as `bin/test` and the Rust Tests jobs do. Dev-dependencies add features to crates such as `hyper` and `getrandom`, so a plain `cargo build` resolves a different feature set, and the `cargo test` after it compiles a second copy of every dependency above them, DuckDB, RocksDB, polars, and the AWS SDK included.

bin/test

@@ -2,9 +2,12 @@
 #
 # Build, configure, and run the Oxen test suite.
 #
-# Usage: bin/test [--ffmpeg] [--keep] [--install-deps] [--no-ramdisk] [--timings] [-p|--python] [extra args...]
+# Usage: bin/test [--ffmpeg] [--keep] [--install-deps] [--no-ramdisk] [--timings] [-p|--python]
+#                 [--build-only] [extra args...]
 #
 #   --ffmpeg        Enable the "ffmpeg" cargo feature for build and test commands.
+#   --build-only    Run the build a Rust test run starts with, then exit, leaving test data alone.
+#                   Not with -p.
 #   --keep          Do not remove test data (in data/ox and data/test/runs) on cleanup — useful for
 #                   debugging failed tests.
 #   --install-deps  Check and install prerequisites (install-prereqs) before running tests.
@@ -92,9 +95,11 @@ INSTALL_DEPS=false
 RUN_PYTHON=false
 USE_RAMDISK=true
 TIMINGS=false
+BUILD_ONLY=false
 while true; do
     case "${1:-}" in
         --ffmpeg)        FEATURE_ARGS="-F ffmpeg"; shift ;;
+        --build-only)    BUILD_ONLY=true; shift ;;
         --keep)          KEEP_DATA=true; shift ;;
         --install-deps)  INSTALL_DEPS=true; shift ;;
         --no-ramdisk)    USE_RAMDISK=false; shift ;;
@@ -106,6 +111,11 @@ done
 
 set -euo pipefail
 
+if [ "$BUILD_ONLY" = true ] && [ "$RUN_PYTHON" = true ]; then
+    echo "ERROR: --build-only runs the Rust build and cannot be combined with -p."
+    exit 2
+fi
+
 # On Linux the `ffmpeg` feature links FFmpeg 9 from /opt/ffmpeg (installed by bin/install-prereqs);
 # point pkg-config at it. macOS gets FFmpeg 9 from Homebrew, already on the default pkg-config path.
 if [ -n "$FEATURE_ARGS" ] && [ "$(uname)" = "Linux" ]; then
@@ -201,7 +211,9 @@ cleanup() {
     if [ -n "$PYTHON_CONFIG_DIR" ]; then
         rm -rf "$PYTHON_CONFIG_DIR"
     fi
-    if [ "$KEEP_DATA" = false ]; then
+    if [ "$BUILD_ONLY" = true ]; then
+        :
+    elif [ "$KEEP_DATA" = false ]; then
         echo "==> Removing test data..."
         rm -rf ./data/ox
         rm -rf ./data/test/runs
@@ -216,7 +228,9 @@ cleanup() {
 trap cleanup EXIT INT TERM
 
 # Set up ramdisk for test data
-if [ "$USE_RAMDISK" = true ]; then
+if [ "$BUILD_ONLY" = true ]; then
+    :
+elif [ "$USE_RAMDISK" = true ]; then
     if ! setup_ramdisk; then
         echo "==> Ramdisk setup failed, using regular filesystem."
     fi
@@ -236,6 +250,10 @@ echo "==> Building oxen (cargo build --workspace --bins --tests $FEATURE_ARGS)..
 # shellcheck disable=SC2086
 cargo build --workspace --bins --tests $FEATURE_ARGS
 
+if [ "$BUILD_ONLY" = true ]; then
+    exit 0
+fi
+
 phase "Server start"
 
 # Verify ulimit