chore(build): pin bun + CI cache hygiene

.github/actions/setup-hugo/action.yml

@@ -23,6 +23,8 @@ runs:
         extended: true
 
     - uses: oven-sh/setup-bun@v2
+      with:
+        bun-version: latest
 
     - name: Cache Bun dependencies
       uses: actions/cache@v5

.github/workflows/_hugo.yml

@@ -5,7 +5,6 @@ on:
 
 env:
   HUGO_ENVIRONMENT: production
-  HUGO_CACHEDIR: /tmp/hugo_cache
 
 
 jobs:
@@ -42,7 +41,9 @@ jobs:
             ${{ runner.os }}-deps-
 
       - uses: oven-sh/setup-bun@v2
-      - run: bun install
+        with:
+          bun-version: latest
+      - run: bun install --frozen-lockfile
 
       # Use Bun as the "node" runtime for Hugo's PostCSS pipeline.
       # Hugo 0.161+ runs Node tools with --permission flags; Bun ignores
@@ -54,30 +55,23 @@ jobs:
           ln -sf "$(which bun)" "$HOME/.bun-as-node/node"
           echo "$HOME/.bun-as-node" >> "$GITHUB_PATH"
 
-      # Tier 2: Hugo build cache (changes with any build-affecting file)
+      # Tier 2a: Hugo image cache (survives CSS/HTML changes)
       - uses: actions/cache@v5
-        name: Cache Hugo build resources
+        name: Cache Hugo processed images
         with:
-          path: |
-            ${{ env.HUGO_CACHEDIR }}
-            resources/_gen
-          key: ${{ runner.os }}-hugo-build-${{ hashFiles('hugo.toml', 'hugo.dev.toml', 'postcss.config.js', 'package.json', 'themes/**', 'layouts/**') }}
+          path: resources/_gen/images
+          key: ${{ runner.os }}-hugo-images-${{ hashFiles('assets/**', 'content/**/*.jpg', 'content/**/*.jpeg', 'content/**/*.png', 'content/**/*.webp', 'content/**/*.gif', 'content/**/*.svg', 'static/**', 'themes/**/static/**', 'themes/**/assets/images/**') }}
           restore-keys: |
-            ${{ runner.os }}-hugo-build-
-            ${{ runner.os }}-hugo-
+            ${{ runner.os }}-hugo-images-
 
-      # Tier 3: Content and template cache (comprehensive file tracking)
+      # Tier 2b: Hugo asset cache (CSS/JS compilation, updates on theme/config changes)
       - uses: actions/cache@v5
-        name: Cache Hugo content and assets
+        name: Cache Hugo asset compilation
         with:
-          path: |
-            public
-            hugo_stats.json
-          key: ${{ runner.os }}-hugo-content-${{ hashFiles('content/**', 'data/**', 'assets/**', 'static/**', 'layouts/**', 'themes/**/*.html', 'themes/**/*.scss', 'themes/**/*.js', 'hugo.toml', 'hugo.dev.toml', 'postcss.config.js') }}
+          path: resources/_gen/assets
+          key: ${{ runner.os }}-hugo-assets-${{ hashFiles('themes/**', 'layouts/**', 'postcss.config.js', 'package.json', 'hugo.toml', 'hugo.dev.toml') }}
           restore-keys: |
-            ${{ runner.os }}-hugo-content-${{ hashFiles('content/**', 'data/**', 'assets/**', 'static/**') }}
-            ${{ runner.os }}-hugo-content-${{ hashFiles('content/**', 'data/**') }}
-            ${{ runner.os }}-hugo-content-
+            ${{ runner.os }}-hugo-assets-
 
       - name: Build with Hugo
         run: |