Encapsulate job pool behind a single handle (job_pool_*)

Replace the four-parallel-nameref job-pool API (pids/statuses/labels/failed,
each needing its own `shellcheck disable=SC2034` at every call site) with a
single pool handle: a name prefix whose four backing variables
(${pool}_pids/_statuses/_labels/_failed) are derived on demand by the helpers.
Bash can't nest indexed arrays in an associative array, so a prefixed-handle
with declare -g backing vars is the simplest pure-nameref encoding (no eval).

New public API:
  job_pool_init <pool>
  job_pool_submit <pool> <label> <cmd...>
  job_pool_wait <pool>            # returns 1 if any job failed

Migrate all callers (scalephotos, create_all_photo_derivatives,
render_album_pages, render_view_redirects, render_filter_pages) to the handle.
queue_preview_page_render_job / queue_album_view_render_job /
_album_record_view_photo / _stats_enqueue_filter_album now take one pool arg
instead of four names.

Drop the dead wrappers and unused parameterization: wait_for_image_job_slot,
wait_for_template_render_job_slot and their _jobs variants only ever passed
IMAGE_JOBS, so the max_jobs parameter is gone and throttling is fixed at
IMAGE_JOBS inside the pool. Also removes wait_for_album_view_render_jobs (now
just job_pool_wait).

Throttling (max IMAGE_JOBS concurrent), failure detection and failed-job
propagation are unchanged; the parallel-throttling and failure-logging tests
pass unmodified. SC2034 disable-comments across the touched files drop 29->7.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

1 files changed, 8 insertions, 27 deletions

diff --git a/src/lib/image-pipeline.source.sh b/src/lib/image-pipeline.source.sh
index 876501b..934c3b5 100644
--- a/src/lib/image-pipeline.source.sh
+++ b/src/lib/image-pipeline.source.sh
@@ -38,41 +38,22 @@ create_all_photo_derivatives() {
     local -r photos_dir="$1"; shift
     local -r thumbs_dir="$1"; shift
     local -r blurs_dir="$1"; shift
-    local -i failed=0
-    local -a image_job_pids=()
-    # Passed by name to wait_for_image_job_slot and wait_for_image_jobs.
-    # shellcheck disable=SC2034
-    local -A image_job_labels=()
-    # Passed by name to wait_for_image_job_slot and wait_for_image_jobs.
-    # shellcheck disable=SC2034
-    local -A image_job_statuses=()
     local photo
 
+    # Throttled background job pool (max IMAGE_JOBS concurrent), addressed by the
+    # single handle "image_jobs". job_pool_wait returns 1 if any job failed.
+    job_pool_init image_jobs
+
     while IFS= read -r photo; do
-        wait_for_image_job_slot \
-            image_job_pids \
-            image_job_statuses \
-            image_job_labels \
-            failed
-        create_photo_derivatives "$photos_dir" "$thumbs_dir" "$blurs_dir" \
-            "$photo" &
-        image_job_pids+=("$!")
-        # Read through a nameref in the job-pool helpers.
-        # shellcheck disable=SC2034
-        image_job_labels["$!"]="image derivative job for photo $photo"
+        job_pool_submit image_jobs "image derivative job for photo $photo" \
+            create_photo_derivatives "$photos_dir" "$thumbs_dir" "$blurs_dir" \
+            "$photo"
     done < <(
         find "$DIST_DIR/$photos_dir" -maxdepth 1 -type f -printf '%f\n' \
             | sort
     )
 
-    wait_for_image_jobs \
-        image_job_pids \
-        image_job_statuses \
-        image_job_labels \
-        failed
-    if (( failed != 0 )); then
-        return 1
-    fi
+    job_pool_wait image_jobs
 }
 
 prepare_generation_photo_assets() {