fix(ci): give each xvfb-run its own display (#230)

Every `process-cran-updates-ubuntu-2204-arm64` cron run since pipeline 13744 has failed with `xvfb-run: error: Xvfb failed to start` (e.g. 13829).

## Cause

The newer-R loop added in #216 runs two `xvfb-run` calls back to back: the R-minor-sensitive `process_cran_updates` pass, then `local/build-newer-r.R`.
Without `-a`, `xvfb-run` always uses display `:99`, and on exit it kills its Xvfb without waiting for it.
The second call can therefore start while the old server still holds the `:99` lock, so the new Xvfb refuses to start.
Only ubuntu-2204-arm64 hits this because it is the only image with a second R minor installed, so the loop body only runs there.

## Change

- Default `XVFB_ARGS` to `-a` (`--auto-servernum`) in `process-updates.yaml`, `build-all-versions.yaml` and `weekly-rebuild-missing.yaml`, so each call picks a free display.
- The RHEL 10 `xwfb-run` branch still overrides `XVFB_ARGS` with `-c weston`, so it is unchanged.

## Verification

`crow lint .crow/` passes.
A local repro was not possible (`docker run` hangs on the dev host), so the next ubuntu-2204-arm64 cron run is the real check.

Reviewed-on: #230

.crow/build-all-versions.yaml

@@ -153,7 +153,7 @@ steps:
       # not visible here. Install the packages needed to recompute the snapshot
       # and query build metadata in every build job.
       - UVR_R_BIN=/opt/R/$R_VERSION/bin/R local/uvr-install.sh RPostgres s3fs data.table future jsonlite
-      - XVFB=$(command -v xwfb-run 2>/dev/null || command -v xvfb-run); XVFB_ARGS=""; if command -v xwfb-run >/dev/null 2>&1; then dnf install -y -q weston 2>/dev/null; XVFB_ARGS="-c weston"; fi
+      - XVFB=$(command -v xwfb-run 2>/dev/null || command -v xvfb-run); XVFB_ARGS="-a"; if command -v xwfb-run >/dev/null 2>&1; then dnf install -y -q weston 2>/dev/null; XVFB_ARGS="-c weston"; fi
       - $XVFB $XVFB_ARGS -n $SPLIT_INDEX -- /opt/R/$R_VERSION/bin/Rscript local/build-all.R $SPLIT_INTO $SPLIT_INDEX $NCPUS 2>&1
       - |
         PRIMARY_MINOR=$(echo "$R_VERSION" | cut -d. -f1-2)

.crow/process-updates.yaml

@@ -192,7 +192,7 @@ steps:
       - UVR_R_BIN=/opt/R/$R_VERSION/bin/R local/uvr-install.sh RPostgres
       - /opt/R/$R_VERSION/bin/R -q -e 'packageVersion("bincraft")'
       # rhel-10 ships xwfb-run (Xwayland) instead of xvfb-run; prefer it and start weston, else fall back to xvfb-run
-      - XVFB=$(command -v xwfb-run 2>/dev/null || command -v xvfb-run); XVFB_ARGS=""; if command -v xwfb-run >/dev/null 2>&1; then dnf install -y -q weston 2>/dev/null; XVFB_ARGS="-c weston"; fi
+      - XVFB=$(command -v xwfb-run 2>/dev/null || command -v xvfb-run); XVFB_ARGS="-a"; if command -v xwfb-run >/dev/null 2>&1; then dnf install -y -q weston 2>/dev/null; XVFB_ARGS="-c weston"; fi
       # options(future.globals.onReference = NULL): for some reason s3fs::file_delete() throws 'Error: Detected a non-exportable reference ('externalptr') in one of the globals ('FUN' of class 'function') used in the future expression' otherwise
       - $XVFB $XVFB_ARGS -- /opt/R/$R_VERSION/bin/R -q -e "options(crayon.enabled = TRUE, Ncpus = 4, future.globals.onReference = 'error', repos = structure(c(getOption('repos'),INLA='https://inla.r-inla-download.org/R/stable'))); progressr::handlers('cli'); progressr::handlers(global = TRUE); options(future.globals.onReference = NULL); bincraft::process_cran_updates(interval = $INTERVAL, platform = '${OS}', process_updated = TRUE, process_new = ${PROCESS_NEW}, process_removed = TRUE, patches = 'local/patches', r_minor_detection = 'classifier',s3_endpoint = 'https://s3.eu-central-003.backblazeb2.com', s3_region = 'eu-central-003', s3_bucket = 'devxy-rpkgs-binaries', s3_access_key_id = Sys.getenv('B2_S3_ACCESS_KEY'), s3_secret_access_key = Sys.getenv('B2_S3_SECRET_KEY'), metadata_db_host = 'r-binaries.devxy.io', metadata_db_name = 'build_metadata', metadata_db_table = 'single_builds', metadata_db_user = 'rpkgs', metadata_db_password = Sys.getenv('PGPASS'), metadata_db_sslmode = 'require', metadata_db_port = 15432, archive = TRUE, upload = TRUE, store_build_metadata = TRUE)"
       - |

.crow/weekly-rebuild-missing.yaml

@@ -388,7 +388,7 @@ steps:
       - rm -rf /mnt/cache/R-pkgs/00LOCK-*
       - /opt/R/$R_VERSION/bin/Rscript local/install-bincraft.R
       - /opt/R/$R_VERSION/bin/R -q -e 'packageVersion("bincraft")'
-      - XVFB=$(command -v xwfb-run 2>/dev/null || command -v xvfb-run); XVFB_ARGS=""; if command -v xwfb-run >/dev/null 2>&1; then dnf install -y -q weston 2>/dev/null; XVFB_ARGS="-c weston"; fi
+      - XVFB=$(command -v xwfb-run 2>/dev/null || command -v xvfb-run); XVFB_ARGS="-a"; if command -v xwfb-run >/dev/null 2>&1; then dnf install -y -q weston 2>/dev/null; XVFB_ARGS="-c weston"; fi
       - UVR_R_BIN=/opt/R/$R_VERSION/bin/R local/uvr-install.sh httr2
       - /opt/R/$R_VERSION/bin/R -q -e 'source("local/fetch-rebuild-packages-from-issue.R")'
       - $XVFB $XVFB_ARGS -n $SPLIT_INDEX -- /opt/R/$R_VERSION/bin/Rscript local/rebuild-missing.R $SPLIT_INTO $SPLIT_INDEX $REBUILD_BUDGET_HOURS 2>&1