in0 split album.source.sh into cohesive modules

Refactor the ~1442-line album.source.sh ([SRP] violation) into three
cohesive modules, leaving album.source.sh a thin coordinator. Pure code
move, no behavior change -- whole functions and their doc comments moved
verbatim; the assembled bin/shuriken contains the same function set.

- image-pipeline.source.sh: ImageMagick derivative generation
  (create_photo_derivatives, create_all_photo_derivatives) and photo
  asset prep (prepare_generation_photo_assets).
- album-metadata.source.sh: EXIF identify caching, exif tooltip/details
  helpers, file counts, shuriken.json metadata, EXIF cache clearing and
  the dry-run plan.
- album-render.source.sh: preview/view/details/splash/redirect page
  rendering, the parallel render-job orchestration and the
  ALBUM_VIEW_PAGE_BY_PHOTO global.
- album.source.sh: thin coordinator (generate, refresh_splash,
  generate_stats_pages, site-asset/archive/html-clean helpers).

Add the three modules to LIB_SOURCES (Justfile) and to the
SHURIKEN_LIB_SOURCES markers in src/shuriken.sh, ordered after random
and before album.source.sh / stats.source.sh.

just build, just test, just shellcheck, just check-generated and
git diff --check all pass.

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

1 files changed, 84 insertions, 0 deletions

diff --git a/src/lib/image-pipeline.source.sh b/src/lib/image-pipeline.source.sh
new file mode 100644
index 0000000..876501b
--- /dev/null
+++ b/src/lib/image-pipeline.source.sh
@@ -0,0 +1,84 @@
+create_photo_derivatives() {
+    local -r photos_dir="$1"; shift
+    local -r thumbs_dir="$1"; shift
+    local -r blurs_dir="$1"; shift
+    local -r photo="$1"; shift
+    local dirname
+    local height
+
+    if [[ -f "$DIST_DIR/$thumbs_dir/$photo" \
+        && -f "$DIST_DIR/$blurs_dir/$photo" ]]; then
+        log_verbose "Skipped existing thumb and blur" \
+            "$(_display_path "$DIST_DIR/$thumbs_dir/$photo") and" \
+            "$(_display_path "$DIST_DIR/$blurs_dir/$photo")"
+        return
+    fi
+
+    dirname="$DIST_DIR/$thumbs_dir"
+    mkdir -p "$dirname"
+    log_info "Creating thumb $(_display_path "$DIST_DIR/$thumbs_dir/$photo")"
+    # Double the height, as CSS scales images based on boxing too.
+    height=$(( THUMBHEIGHT * 2 ))
+    imagemagick \
+        "$DIST_DIR/$photos_dir/$photo" \
+        -geometry "x$height" \
+        "$DIST_DIR/$thumbs_dir/$photo"
+
+    dirname="$DIST_DIR/$blurs_dir"
+    mkdir -p "$dirname"
+    log_info "Creating blur $(_display_path "$DIST_DIR/$blurs_dir/$photo")"
+    imagemagick \
+        "$DIST_DIR/$thumbs_dir/$photo" \
+        -flip \
+        -blur 0x8 \
+        "$DIST_DIR/$blurs_dir/$photo"
+}
+
+create_all_photo_derivatives() {
+    local -r photos_dir="$1"; shift
+    local -r thumbs_dir="$1"; shift
+    local -r blurs_dir="$1"; shift
+    local -i failed=0
+    local -a image_job_pids=()
+    # Passed by name to wait_for_image_job_slot and wait_for_image_jobs.
+    # shellcheck disable=SC2034
+    local -A image_job_labels=()
+    # Passed by name to wait_for_image_job_slot and wait_for_image_jobs.
+    # shellcheck disable=SC2034
+    local -A image_job_statuses=()
+    local photo
+
+    while IFS= read -r photo; do
+        wait_for_image_job_slot \
+            image_job_pids \
+            image_job_statuses \
+            image_job_labels \
+            failed
+        create_photo_derivatives "$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 $photo"
+    done < <(
+        find "$DIST_DIR/$photos_dir" -maxdepth 1 -type f -printf '%f\n' \
+            | sort
+    )
+
+    wait_for_image_jobs \
+        image_job_pids \
+        image_job_statuses \
+        image_job_labels \
+        failed
+    if (( failed != 0 )); then
+        return 1
+    fi
+}
+
+prepare_generation_photo_assets() {
+    warn_unsupported_incoming_files
+    mkdir -p "$DIST_DIR/photos"
+    cleanphotos
+    scalephotos
+    create_all_photo_derivatives 'photos' 'thumbs' 'blurs'
+}