diff --git a/action.yaml b/action.yaml
index 16eaa59..791e24a 100644
--- a/action.yaml
+++ b/action.yaml
@@ -65,480 +65,33 @@ runs:
 
   - name: Install and Verify Trivy
     shell: bash
-    run: |
-      set -euo pipefail
-
-      mkdir -p "$HOME/.local/bin" "$HOME/.cache/trivy-bin"
-      echo "$HOME/.local/bin" >> "$GITHUB_PATH"
-      ARCH="$(uname -m)"
-      case "${ARCH}" in
-        x86_64) T_ARCH="64bit" ;;
-        aarch64|arm64) T_ARCH="ARM64" ;;
-        *) echo "::error::Unsupported architecture: ${ARCH}"; exit 1 ;;
-      esac
-
-      checksums_file="${{ github.action_path }}/checksums.txt"
-      tarball="trivy_${{ steps.vars.outputs.version }}_Linux-${T_ARCH}.tar.gz"
-
-      if [ -f "$HOME/.cache/trivy-bin/${tarball}" ] && (cd "$HOME/.cache/trivy-bin" && grep "  ${tarball}$" "$checksums_file" | sha256sum -c -); then
-        echo "Cached Trivy archive verified against lockfile."
-      else
-        echo "Archive missing or checksum mismatch; downloading..."
-        curl -sfLO "https://github.com/aquasecurity/trivy/releases/download/v${{ steps.vars.outputs.version }}/${tarball}" --output-dir "$HOME/.cache/trivy-bin"
-        (cd "$HOME/.cache/trivy-bin" && grep "  ${tarball}$" "$checksums_file" | sha256sum -c -)
-      fi
-
-      tar -xzf "$HOME/.cache/trivy-bin/${tarball}" -C "$HOME/.local/bin" trivy
-      chmod +x "$HOME/.local/bin/trivy"
+    env:
+      TRIVY_VERSION: ${{ steps.vars.outputs.version }}
+    run: node "${{ github.action_path }}/lib/install-trivy.js"
 
   - name: Extract Multi-Platform SBOMs
     shell: bash
-    run: |
-      export PATH="$HOME/.local/bin:$PATH"
-      export TRIVY_SKIP_VERSION_CHECK="true"
-      mkdir -p sboms/head sboms/target
-
-      cleanup_file() {
-        local f="$1"
-        if [ -f "$f" ]; then
-          if [ ! -s "$f" ] || [ "$(cat "$f" 2>/dev/null)" = "null" ]; then
-            rm -f "$f"
-          fi
-        fi
-      }
-
-      head_sbom_err=""
-      target_sbom_err=""
-      use_inbuild="${{ inputs.use-inbuild-sbom }}"
-
-      # Determine target platforms / architectures
-      PLATFORMS=()
-      if [ -n "${{ inputs.architectures }}" ]; then
-        IFS=',' read -ra RAW_ARCHS <<< "${{ inputs.architectures }}"
-        for a in "${RAW_ARCHS[@]}"; do
-          clean_a=$(echo "$a" | xargs)
-          [ -z "$clean_a" ] && continue
-          if [[ "$clean_a" != *"/"* ]]; then
-            PLATFORMS+=("linux/${clean_a}")
-          else
-            PLATFORMS+=("$clean_a")
-          fi
-        done
-      else
-        echo "Auto-discovering architectures from images..."
-        raw_head=$(docker buildx imagetools inspect --raw "${{ inputs.head-image }}" 2>/dev/null || true)
-        raw_target=$(docker buildx imagetools inspect --raw "${{ inputs.target-image }}" 2>/dev/null || true)
-
-        discovered=$(node -e '
-          const raw1 = process.argv[1];
-          const raw2 = process.argv[2];
-          const set = new Set();
-          for (const raw of [raw1, raw2]) {
-            if (!raw) continue;
-            try {
-              const data = JSON.parse(raw);
-              const manifests = data.manifests || [];
-              for (const m of manifests) {
-                if (m.platform && m.platform.architecture && m.platform.architecture !== "unknown") {
-                  const os = m.platform.os || "linux";
-                  const variant = m.platform.variant ? "/" + m.platform.variant : "";
-                  set.add(`${os}/${m.platform.architecture}${variant}`);
-                }
-              }
-            } catch (e) {}
-          }
-          console.log(Array.from(set).sort().join("\n"));
-        ' "$raw_head" "$raw_target")
-
-        if [ -n "$discovered" ]; then
-          while IFS= read -r line; do
-            [ -n "$line" ] && PLATFORMS+=("$line")
-          done <<< "$discovered"
-        fi
-      fi
-
-      echo "Configured platforms: ${PLATFORMS[*]:-(single platform fallback)}"
-      if [ "$use_inbuild" = "true" ]; then
-        echo "ℹ️  Strategy: Built-in SBOM attestation extraction enabled (Docker Scout / Syft). Skips container layer downloads for maximum speed."
-        echo "ℹ️  Note: Built-in SBOM vulnerability counts may differ from direct filesystem scans ('trivy image') due to binary vs. source package tracking."
-      else
-        echo "ℹ️  Strategy: Direct Trivy image scanning enabled (default). Inspects full container rootfs and package databases for maximum fidelity."
-      fi
-
-      for platform in "${PLATFORMS[@]}"; do
-        arch_tag=$(echo "$platform" | sed -e 's#^[a-zA-Z0-9_-]*/##' -e 's#/#-#g')
-
-        # Head image extraction & fallback
-        if [ "$use_inbuild" = "true" ]; then
-          echo "Attempting extraction of built-in SBOM for head image ($platform)..."
-          docker buildx imagetools inspect "${{ inputs.head-image }}" \
-            --format "{{ json (index .SBOM \"${platform}\").SPDX }}" > "sboms/head/sbom-${arch_tag}.spdx.json" 2>/dev/null || true
-          cleanup_file "sboms/head/sbom-${arch_tag}.spdx.json"
-          [ -f "sboms/head/sbom-${arch_tag}.spdx.json" ] && cp "sboms/head/sbom-${arch_tag}.spdx.json" "sboms/head/inbuild-sbom-${arch_tag}.spdx.json" 2>/dev/null || true
-        fi
-
-        if [ ! -f "sboms/head/sbom-${arch_tag}.spdx.json" ]; then
-          echo "Generating SBOM for head image ($platform) with Trivy..."
-          if ! trivy image --skip-version-check --platform "$platform" --format spdx-json --output "sboms/head/sbom-${arch_tag}.spdx.json" "${{ inputs.head-image }}"; then
-            echo "::warning::Trivy image scan failed for head image ($platform)"
-          fi
-          cleanup_file "sboms/head/sbom-${arch_tag}.spdx.json"
-        fi
-
-        # Target image extraction & fallback
-        if [ "$use_inbuild" = "true" ]; then
-          echo "Attempting extraction of built-in SBOM for target image ($platform)..."
-          docker buildx imagetools inspect "${{ inputs.target-image }}" \
-            --format "{{ json (index .SBOM \"${platform}\").SPDX }}" > "sboms/target/sbom-${arch_tag}.spdx.json" 2>/dev/null || true
-          cleanup_file "sboms/target/sbom-${arch_tag}.spdx.json"
-          [ -f "sboms/target/sbom-${arch_tag}.spdx.json" ] && cp "sboms/target/sbom-${arch_tag}.spdx.json" "sboms/target/inbuild-sbom-${arch_tag}.spdx.json" 2>/dev/null || true
-        fi
-
-        if [ ! -f "sboms/target/sbom-${arch_tag}.spdx.json" ]; then
-          echo "Generating SBOM for target image ($platform) with Trivy..."
-          if ! trivy image --skip-version-check --platform "$platform" --format spdx-json --output "sboms/target/sbom-${arch_tag}.spdx.json" "${{ inputs.target-image }}"; then
-            echo "::warning::Trivy image scan failed for target image ($platform)"
-          fi
-          cleanup_file "sboms/target/sbom-${arch_tag}.spdx.json"
-        fi
-      done
-
-      # Fallbacks if no platform-specific SBOMs were extracted (e.g. single-arch image without index)
-      if [ -z "$(find sboms/head -type f -name 'sbom-*.spdx.json' 2>/dev/null)" ]; then
-        if [ "$use_inbuild" = "true" ]; then
-          docker buildx imagetools inspect "${{ inputs.head-image }}" \
-            --format '{{ json .SBOM.SPDX }}' > sboms/head/sbom-default.spdx.json 2>/dev/null || true
-          cleanup_file sboms/head/sbom-default.spdx.json
-          [ -f sboms/head/sbom-default.spdx.json ] && cp sboms/head/sbom-default.spdx.json sboms/head/inbuild-sbom-default.spdx.json 2>/dev/null || true
-        fi
-
-        if [ ! -f sboms/head/sbom-default.spdx.json ]; then
-          echo "Generating default head SBOM directly with Trivy..."
-          if ! trivy image --skip-version-check --format spdx-json --output sboms/head/sbom-default.spdx.json "${{ inputs.head-image }}"; then
-            head_sbom_err="Failed to generate SBOM with Trivy for head image"
-          fi
-          cleanup_file sboms/head/sbom-default.spdx.json
-        fi
-      fi
-
-      if [ -z "$(find sboms/target -type f -name 'sbom-*.spdx.json' 2>/dev/null)" ]; then
-        if [ "$use_inbuild" = "true" ]; then
-          docker buildx imagetools inspect "${{ inputs.target-image }}" \
-            --format '{{ json .SBOM.SPDX }}' > sboms/target/sbom-default.spdx.json 2>/dev/null || true
-          cleanup_file sboms/target/sbom-default.spdx.json
-          [ -f sboms/target/sbom-default.spdx.json ] && cp sboms/target/sbom-default.spdx.json sboms/target/inbuild-sbom-default.spdx.json 2>/dev/null || true
-        fi
-
-        if [ ! -f sboms/target/sbom-default.spdx.json ]; then
-          echo "Generating default target SBOM directly with Trivy..."
-          if ! trivy image --skip-version-check --format spdx-json --output sboms/target/sbom-default.spdx.json "${{ inputs.target-image }}"; then
-            target_sbom_err="Failed to generate SBOM with Trivy for target image"
-          fi
-          cleanup_file sboms/target/sbom-default.spdx.json
-        fi
-      fi
-
-      shopt -s nullglob
-      head_files=(sboms/head/sbom-*.spdx.json)
-      target_files=(sboms/target/sbom-*.spdx.json)
-
-      if [ ${#head_files[@]} -eq 0 ] && [ -z "$head_sbom_err" ]; then
-        head_sbom_err="No SBOM generated and head image could not be inspected"
-      fi
-
-      if [ ${#target_files[@]} -eq 0 ] && [ -z "$target_sbom_err" ]; then
-        target_sbom_err="No SBOM generated and target baseline image could not be inspected"
-      fi
-
-      # Diagnostic overview
-      echo ""
-      echo "================================================================================"
-      echo "                      SBOM EXTRACTION DIAGNOSTIC OVERVIEW                       "
-      echo "================================================================================"
-      if [ -n "$head_sbom_err" ]; then
-        echo "HEAD Image (${{ inputs.head-image }}): ❌ FAILED - $head_sbom_err"
-      else
-        echo "HEAD Image (${{ inputs.head-image }}): ✅ SUCCESS"
-        for f in "${head_files[@]}"; do
-          echo "  - $(basename "$f") ($(wc -c < "$f") bytes)"
-        done
-      fi
-
-      if [ -n "$target_sbom_err" ]; then
-        echo "TARGET Baseline Image (${{ inputs.target-image }}): ❌ FAILED - $target_sbom_err"
-      else
-        echo "TARGET Baseline Image (${{ inputs.target-image }}): ✅ SUCCESS"
-        for f in "${target_files[@]}"; do
-          echo "  - $(basename "$f") ($(wc -c < "$f") bytes)"
-        done
-      fi
-      echo "================================================================================"
-      echo ""
-
-      has_sbom_err=false
-      if [ -n "$head_sbom_err" ]; then
-        echo "::error::Head SBOM extraction failed: $head_sbom_err"
-        has_sbom_err=true
-      fi
-      if [ -n "$target_sbom_err" ]; then
-        echo "::error::Target baseline SBOM extraction failed: $target_sbom_err"
-        has_sbom_err=true
-      fi
-
-      if [ "$has_sbom_err" = "true" ]; then
-        echo "::error::Both head and target images must have valid SBOMs to proceed with differential scanning."
-        exit 1
-      fi
-
-      # Expose extracted head SBOMs to workspace root for workflow artifact uploads
-      for f in sboms/head/sbom-*.spdx.json; do
-        [ -f "$f" ] || continue
-        cp "$f" "$(basename "$f")" || true
-      done
+    env:
+      PATH: ${{ env.HOME }}/.local/bin:${{ env.PATH }}
+      TRIVY_SKIP_VERSION_CHECK: 'true'
+      INPUT_HEAD_IMAGE: ${{ inputs.head-image }}
+      INPUT_TARGET_IMAGE: ${{ inputs.target-image }}
+      INPUT_ARCHITECTURES: ${{ inputs.architectures }}
+      INPUT_USE_INBUILD_SBOM: ${{ inputs.use-inbuild-sbom }}
+    run: node "${{ github.action_path }}/lib/extract-sboms.js"
 
   - name: Scan Multi-Platform SBOMs and Generate Delta
     shell: bash
-    run: |
-      export PATH="$HOME/.local/bin:$PATH"
-      export TRIVY_SKIP_VERSION_CHECK="true"
-      mkdir -p cve-reports/head cve-reports/target
-
-      shopt -s nullglob
-      head_sboms=(sboms/head/sbom-*.spdx.json)
-      target_sboms=(sboms/target/sbom-*.spdx.json)
-
-      head_ok=true
-      target_ok=true
-      head_report_count=0
-      target_report_count=0
-
-      head_summary=()
-      target_summary=()
-      use_inbuild="${{ inputs.use-inbuild-sbom }}"
-
-      detect_distro() {
-        node -e '
-          const fs = require("fs");
-          try {
-            const data = JSON.parse(fs.readFileSync(process.argv[1], "utf8"));
-            let name, ver;
-            for (const pkg of (data.packages || [])) {
-              for (const ref of (pkg.externalRefs || [])) {
-                if (ref.referenceType === "purl" && ref.referenceLocator) {
-                  const mName = ref.referenceLocator.match(/[?&]os_name=([^&]+)/);
-                  const mVer = ref.referenceLocator.match(/[?&]os_version=([^&]+)/);
-                  if (mName && mVer) {
-                    name = mName[1];
-                    ver = mVer[1];
-                    break;
-                  }
-                }
-              }
-              if (name && ver) break;
-            }
-            if (name && ver) console.log(name + "/" + ver);
-          } catch (e) {}
-        ' "$1" 2>/dev/null || true
-      }
-
-      # 1. Scan Head SBOMs
-      if [ ${#head_sboms[@]} -eq 0 ]; then
-        head_ok=false
-        head_summary+=("  - ❌ No SBOM files found in sboms/head/")
-      else
-        for f in "${head_sboms[@]}"; do
-          arch=$(basename "$f" .spdx.json | sed 's/sbom-//')
-          out_json="cve-reports/head/cve-${arch}.json"
-          err_log="cve-reports/head/cve-${arch}.err"
-
-          echo "Scanning head SBOM for architecture: $arch"
-          distro_arg=""
-          if [ "$use_inbuild" = "true" ]; then
-            detected_distro=$(detect_distro "$f")
-            if [ -n "$detected_distro" ]; then
-              echo "Detected distribution '${detected_distro}' from in-build SBOM PURLs. Scanning with --distro."
-              distro_arg="--distro ${detected_distro}"
-            fi
-          fi
-
-          scan_success=false
-          if trivy sbom $distro_arg --skip-version-check --format json --output "$out_json" "$f" 2>"$err_log"; then
-            scan_success=true
-          fi
-
-          vuln_cnt=0
-          if [ -s "$out_json" ]; then
-            cnt=$(grep -c '"VulnerabilityID"' "$out_json" 2>/dev/null || true)
-            cnt=$(echo "$cnt" | tr -d '[:space:]')
-            [ -n "$cnt" ] && vuln_cnt="$cnt"
-          fi
-
-          # Fallback if in-build SBOM scan produced 0 CVEs (e.g. incompatible third-party format) or scan failed
-          if [ "$use_inbuild" = "true" ] && { [ "$scan_success" != "true" ] || [ "$vuln_cnt" -eq 0 ]; }; then
-            echo "::warning::In-build SBOM for head image (${arch}) yielded ${vuln_cnt} CVE findings. Falling back to direct Trivy image scan..."
-            t_plat="linux/${arch}"
-            [ "$arch" = "default" ] && t_plat=""
-            plat_arg=""
-            [ -n "$t_plat" ] && plat_arg="--platform $t_plat"
-            if trivy image --skip-version-check $plat_arg --format spdx-json --output "$f" "${{ inputs.head-image }}"; then
-              echo "Re-scanning head SBOM generated directly by Trivy..."
-              if trivy sbom --skip-version-check --format json --output "$out_json" "$f" 2>"$err_log"; then
-                scan_success=true
-                if [ -s "$out_json" ]; then
-                  cnt=$(grep -c '"VulnerabilityID"' "$out_json" 2>/dev/null || true)
-                  cnt=$(echo "$cnt" | tr -d '[:space:]')
-                  [ -n "$cnt" ] && vuln_cnt="$cnt"
-                fi
-              fi
-            fi
-          fi
-
-          if [ "$scan_success" = "true" ]; then
-            if [ -s "$out_json" ]; then
-              if [ "$vuln_cnt" -eq 0 ]; then
-                echo "::warning::Head image architecture '${arch}' has 0 CVE findings. Verify that OS/packages were recognized."
-                head_summary+=("  - ${arch}: ⚠️ WARNING (0 vulnerability findings detected)")
-              else
-                head_summary+=("  - ${arch}: ✅ OK (${vuln_cnt} vulnerability findings)")
-              fi
-              head_report_count=$((head_report_count + 1))
-            else
-              head_ok=false
-              head_summary+=("  - ${arch}: ❌ FAILED (Output report was empty / 0 bytes)")
-            fi
-          else
-            head_ok=false
-            err_msg=$(tail -n 2 "$err_log" | tr '\n' ' ' | sed 's/  */ /g')
-            [ -z "$err_msg" ] && err_msg="Trivy scan exited with non-zero status"
-            head_summary+=("  - ${arch}: ❌ FAILED (${err_msg})")
-          fi
-        done
-      fi
-
-      # 2. Scan Target SBOMs
-      if [ ${#target_sboms[@]} -eq 0 ]; then
-        target_ok=false
-        target_summary+=("  - ❌ No SBOM files found in sboms/target/")
-      else
-        for f in "${target_sboms[@]}"; do
-          arch=$(basename "$f" .spdx.json | sed 's/sbom-//')
-          out_json="cve-reports/target/cve-${arch}.json"
-          err_log="cve-reports/target/cve-${arch}.err"
-
-          echo "Scanning target SBOM for architecture: $arch"
-          distro_arg=""
-          if [ "$use_inbuild" = "true" ]; then
-            detected_distro=$(detect_distro "$f")
-            if [ -n "$detected_distro" ]; then
-              echo "Detected distribution '${detected_distro}' from in-build SBOM PURLs. Scanning with --distro."
-              distro_arg="--distro ${detected_distro}"
-            fi
-          fi
-
-          scan_success=false
-          if trivy sbom $distro_arg --skip-version-check --format json --output "$out_json" "$f" 2>"$err_log"; then
-            scan_success=true
-          fi
-
-          vuln_cnt=0
-          if [ -s "$out_json" ]; then
-            cnt=$(grep -c '"VulnerabilityID"' "$out_json" 2>/dev/null || true)
-            cnt=$(echo "$cnt" | tr -d '[:space:]')
-            [ -n "$cnt" ] && vuln_cnt="$cnt"
-          fi
-
-          # Fallback if in-build SBOM scan produced 0 CVEs (e.g. incompatible third-party format) or scan failed
-          if [ "$use_inbuild" = "true" ] && { [ "$scan_success" != "true" ] || [ "$vuln_cnt" -eq 0 ]; }; then
-            echo "::warning::In-build SBOM for target image (${arch}) yielded ${vuln_cnt} CVE findings. Falling back to direct Trivy image scan..."
-            t_plat="linux/${arch}"
-            [ "$arch" = "default" ] && t_plat=""
-            plat_arg=""
-            [ -n "$t_plat" ] && plat_arg="--platform $t_plat"
-            if trivy image --skip-version-check $plat_arg --format spdx-json --output "$f" "${{ inputs.target-image }}"; then
-              echo "Re-scanning target SBOM generated directly by Trivy..."
-              if trivy sbom --skip-version-check --format json --output "$out_json" "$f" 2>"$err_log"; then
-                scan_success=true
-                if [ -s "$out_json" ]; then
-                  cnt=$(grep -c '"VulnerabilityID"' "$out_json" 2>/dev/null || true)
-                  cnt=$(echo "$cnt" | tr -d '[:space:]')
-                  [ -n "$cnt" ] && vuln_cnt="$cnt"
-                fi
-              fi
-            fi
-          fi
-
-          if [ "$scan_success" = "true" ]; then
-            if [ -s "$out_json" ]; then
-              if [ "$vuln_cnt" -eq 0 ]; then
-                echo "::warning::Target baseline image architecture '${arch}' has 0 CVE findings. Verify that OS/packages were recognized."
-                target_summary+=("  - ${arch}: ⚠️ WARNING (0 vulnerability findings detected)")
-              else
-                target_summary+=("  - ${arch}: ✅ OK (${vuln_cnt} vulnerability findings)")
-              fi
-              target_report_count=$((target_report_count + 1))
-            else
-              target_ok=false
-              target_summary+=("  - ${arch}: ❌ FAILED (Output report was empty / 0 bytes)")
-            fi
-          else
-            target_ok=false
-            err_msg=$(tail -n 2 "$err_log" | tr '\n' ' ' | sed 's/  */ /g')
-            [ -z "$err_msg" ] && err_msg="Trivy scan exited with non-zero status"
-            target_summary+=("  - ${arch}: ❌ FAILED (${err_msg})")
-          fi
-        done
-      fi
-
-      # 3. Print Comprehensive Diagnostic Overview
-      echo ""
-      echo "================================================================================"
-      echo "                   CVE VULNERABILITY SCAN DIAGNOSTIC OVERVIEW                  "
-      echo "================================================================================"
-      if [ "$use_inbuild" = "true" ]; then
-        echo "Scan Strategy: Built-in OCI Attestation (Syft/Docker Scout) with distro detection"
-      else
-        echo "Scan Strategy: Direct Trivy Image Scan (Full rootfs & source package mapping)"
-      fi
-      echo "--------------------------------------------------------------------------------"
-      echo "HEAD Image: ${{ inputs.head-image }}"
-      for line in "${head_summary[@]}"; do
-        echo "$line"
-      done
-      echo ""
-      echo "TARGET Baseline Image: ${{ inputs.target-image }} (branch: '${{ inputs.target-branch }}')"
-      for line in "${target_summary[@]}"; do
-        echo "$line"
-      done
-      echo "================================================================================"
-      echo ""
-
-      # 4. Enforce Gating: Both must have succeeded with valid reports
-      has_error=false
-      if [ "$head_ok" != "true" ] || [ "$head_report_count" -eq 0 ]; then
-        echo "::error::Head image CVE analysis failed or produced no reports."
-        has_error=true
-      fi
-
-      if [ "$target_ok" != "true" ] || [ "$target_report_count" -eq 0 ]; then
-        echo "::error::Target baseline CVE analysis failed or produced no reports."
-        has_error=true
-      fi
-
-      if [ "$has_error" = "true" ]; then
-        echo "::error::Aborting differential analysis: both head and target scans must succeed before diffing."
-        exit 1
-      fi
-
-      # 5. Run multi-arch set-based diff and generate consolidated full summary report
-      echo "Both head and target scans succeeded. Computing set-based vulnerability delta..."
-      if ! node "${{ github.action_path }}/cve-diff.js" \
-        "cve-reports/target" \
-        "cve-reports/head" \
-        "${{ inputs.target-branch }}" \
-        "${{ inputs.output-summary }}" > "${{ inputs.output-delta }}"; then
-        echo "::error::Failed to generate CVE differential report"
-        exit 1
-      fi
+    env:
+      PATH: ${{ env.HOME }}/.local/bin:${{ env.PATH }}
+      TRIVY_SKIP_VERSION_CHECK: 'true'
+      INPUT_HEAD_IMAGE: ${{ inputs.head-image }}
+      INPUT_TARGET_IMAGE: ${{ inputs.target-image }}
+      INPUT_TARGET_BRANCH: ${{ inputs.target-branch }}
+      INPUT_USE_INBUILD_SBOM: ${{ inputs.use-inbuild-sbom }}
+      INPUT_OUTPUT_DELTA: ${{ inputs.output-delta }}
+      INPUT_OUTPUT_SUMMARY: ${{ inputs.output-summary }}
+    run: node "${{ github.action_path }}/lib/scan-sboms.js"
 
   - name: Publish Reports to Step Summary
     shell: bash
diff --git a/lib/diagnostics.js b/lib/diagnostics.js
new file mode 100644
index 0000000..75b4de3
--- /dev/null
+++ b/lib/diagnostics.js
@@ -0,0 +1,106 @@
+/**
+ * Diagnostic formatting and reporting utilities.
+ */
+
+function formatSbomOverview({
+  headImage,
+  targetImage,
+  headFiles = [],
+  targetFiles = [],
+  headError = null,
+  targetError = null,
+}) {
+  const lines = [
+    '',
+    '================================================================================',
+    '                      SBOM EXTRACTION DIAGNOSTIC OVERVIEW                       ',
+    '================================================================================',
+  ];
+
+  if (headError) {
+    lines.push(`HEAD Image (${headImage}): ❌ FAILED - ${headError}`);
+  } else {
+    lines.push(`HEAD Image (${headImage}): ✅ SUCCESS`);
+    for (const f of headFiles) {
+      lines.push(`  - ${f.name} (${f.size} bytes)`);
+    }
+  }
+
+  if (targetError) {
+    lines.push(`TARGET Baseline Image (${targetImage}): ❌ FAILED - ${targetError}`);
+  } else {
+    lines.push(`TARGET Baseline Image (${targetImage}): ✅ SUCCESS`);
+    for (const f of targetFiles) {
+      lines.push(`  - ${f.name} (${f.size} bytes)`);
+    }
+  }
+
+  lines.push('================================================================================');
+  lines.push('');
+  return lines.join('\n');
+}
+
+function formatScanOverview({
+  headImage,
+  targetImage,
+  targetBranch = 'main',
+  strategy = null,
+  headSummary = [],
+  targetSummary = [],
+}) {
+  const lines = [
+    '',
+    '================================================================================',
+    '                   CVE VULNERABILITY SCAN DIAGNOSTIC OVERVIEW                  ',
+    '================================================================================',
+  ];
+
+  if (strategy) {
+    lines.push(`Scan Strategy: ${strategy}`);
+    lines.push('--------------------------------------------------------------------------------');
+  }
+
+  lines.push(`HEAD Image: ${headImage}`);
+  for (const line of headSummary) {
+    lines.push(line);
+  }
+
+  lines.push('');
+  lines.push(`TARGET Baseline Image: ${targetImage} (branch: '${targetBranch}')`);
+  for (const line of targetSummary) {
+    lines.push(line);
+  }
+
+  lines.push('================================================================================');
+  lines.push('');
+  return lines.join('\n');
+}
+
+function countVulnerabilities(report) {
+  if (!report) return 0;
+  let data = report;
+  if (typeof report === 'string' || Buffer.isBuffer(report)) {
+    try {
+      data = JSON.parse(report.toString('utf8'));
+    } catch {
+      return 0;
+    }
+  }
+  if (!data || typeof data !== 'object') return 0;
+
+  let count = 0;
+  if (Array.isArray(data.Results)) {
+    for (const res of data.Results) {
+      if (res && Array.isArray(res.Vulnerabilities)) {
+        count += res.Vulnerabilities.length;
+      }
+    }
+  }
+  return count;
+}
+
+module.exports = {
+  formatSbomOverview,
+  formatScanOverview,
+  countVulnerabilities,
+};
diff --git a/lib/distro.js b/lib/distro.js
new file mode 100644
index 0000000..6b902a1
--- /dev/null
+++ b/lib/distro.js
@@ -0,0 +1,42 @@
+/**
+ * Distribution detection from SPDX SBOM package PURLs.
+ */
+
+function detectDistro(spdxInput) {
+  if (!spdxInput) return null;
+
+  let data = spdxInput;
+  if (typeof spdxInput === 'string' || Buffer.isBuffer(spdxInput)) {
+    try {
+      data = JSON.parse(spdxInput.toString('utf8'));
+    } catch {
+      return null;
+    }
+  }
+
+  if (!data || typeof data !== 'object' || !Array.isArray(data.packages)) {
+    return null;
+  }
+
+  for (const pkg of data.packages) {
+    if (!pkg || !Array.isArray(pkg.externalRefs)) continue;
+    for (const ref of pkg.externalRefs) {
+      if (ref && ref.referenceType === 'purl' && typeof ref.referenceLocator === 'string') {
+        const purl = ref.referenceLocator;
+        const nameMatch = purl.match(/[?&]os_name=([^&]+)/);
+        const verMatch = purl.match(/[?&]os_version=([^&]+)/);
+        if (nameMatch && verMatch) {
+          const osName = decodeURIComponent(nameMatch[1]);
+          const osVer = decodeURIComponent(verMatch[1]);
+          return `${osName}/${osVer}`;
+        }
+      }
+    }
+  }
+
+  return null;
+}
+
+module.exports = {
+  detectDistro,
+};
diff --git a/lib/extract-sboms.js b/lib/extract-sboms.js
new file mode 100644
index 0000000..7d0d5d1
--- /dev/null
+++ b/lib/extract-sboms.js
@@ -0,0 +1,202 @@
+#!/usr/bin/env node
+
+/**
+ * Extracts or generates multi-platform SBOMs for head and target images.
+ */
+
+const fs = require('node:fs');
+const path = require('node:path');
+const cp = require('node:child_process');
+const { parsePlatforms, discoverPlatforms, toArchTag } = require('./platforms.js');
+const { formatSbomOverview } = require('./diagnostics.js');
+
+function parseArgs(argv) {
+  const args = {
+    headImage: process.env.INPUT_HEAD_IMAGE || '',
+    targetImage: process.env.INPUT_TARGET_IMAGE || '',
+    architectures: process.env.INPUT_ARCHITECTURES || '',
+    useInbuildSbom: process.env.INPUT_USE_INBUILD_SBOM || 'false',
+  };
+
+  for (let i = 2; i < argv.length; i++) {
+    const arg = argv[i];
+    if (arg === '--head-image' && i + 1 < argv.length) args.headImage = argv[++i];
+    else if (arg === '--target-image' && i + 1 < argv.length) args.targetImage = argv[++i];
+    else if (arg === '--architectures' && i + 1 < argv.length) args.architectures = argv[++i];
+    else if (arg === '--use-inbuild-sbom' && i + 1 < argv.length) args.useInbuildSbom = argv[++i];
+  }
+
+  return args;
+}
+
+function cleanupInvalidFile(filePath) {
+  if (!fs.existsSync(filePath)) return;
+  try {
+    const stat = fs.statSync(filePath);
+    if (stat.size === 0) {
+      fs.unlinkSync(filePath);
+      return;
+    }
+    const content = fs.readFileSync(filePath, 'utf8').trim();
+    if (content === 'null' || content === '') {
+      fs.unlinkSync(filePath);
+    }
+  } catch {
+    // Ignore cleanup errors
+  }
+}
+
+function runCommandSafe(cmd, args) {
+  try {
+    return cp.execFileSync(cmd, args, { stdio: ['ignore', 'pipe', 'pipe'] }).toString('utf8');
+  } catch {
+    return null;
+  }
+}
+
+function extractOrGenerateSbom({ image, platform, archTag, outputDir, useInbuild }) {
+  const outputFile = path.join(outputDir, `sbom-${archTag}.spdx.json`);
+  const inbuildFile = path.join(outputDir, `inbuild-sbom-${archTag}.spdx.json`);
+
+  // 1. Attempt in-build SBOM extraction if requested
+  if (useInbuild) {
+    console.log(`Attempting extraction of built-in SBOM for image (${platform})...`);
+    const formatStr = `{{ json (index .SBOM "${platform}").SPDX }}`;
+    const rawSbom = runCommandSafe('docker', ['buildx', 'imagetools', 'inspect', image, '--format', formatStr]);
+    if (rawSbom) {
+      fs.writeFileSync(outputFile, rawSbom);
+      cleanupInvalidFile(outputFile);
+      if (fs.existsSync(outputFile)) {
+        fs.copyFileSync(outputFile, inbuildFile);
+      }
+    }
+  }
+
+  // 2. Fallback to direct Trivy image generation if SBOM not present
+  if (!fs.existsSync(outputFile)) {
+    console.log(`Generating SBOM for image (${platform}) with Trivy...`);
+    const platArgs = platform ? ['--platform', platform] : [];
+    try {
+      cp.execFileSync('trivy', [
+        'image',
+        '--skip-version-check',
+        ...platArgs,
+        '--format', 'spdx-json',
+        '--output', outputFile,
+        image,
+      ], { stdio: 'inherit' });
+    } catch (e) {
+      console.warn(`::warning::Trivy image scan failed for image (${platform}): ${e.message}`);
+    }
+    cleanupInvalidFile(outputFile);
+  }
+}
+
+function main() {
+  const args = parseArgs(process.argv);
+  const { headImage, targetImage, architectures, useInbuildSbom } = args;
+  const useInbuild = useInbuildSbom === 'true';
+
+  if (!headImage || !targetImage) {
+    console.error('::error::Both --head-image and --target-image must be provided.');
+    process.exit(1);
+  }
+
+  const headDir = path.join('sboms', 'head');
+  const targetDir = path.join('sboms', 'target');
+  fs.mkdirSync(headDir, { recursive: true });
+  fs.mkdirSync(targetDir, { recursive: true });
+
+  // Determine platforms
+  let platforms = parsePlatforms(architectures);
+  if (platforms.length === 0) {
+    console.log('Auto-discovering architectures from images...');
+    const rawHead = runCommandSafe('docker', ['buildx', 'imagetools', 'inspect', '--raw', headImage]);
+    const rawTarget = runCommandSafe('docker', ['buildx', 'imagetools', 'inspect', '--raw', targetImage]);
+    platforms = discoverPlatforms(rawHead, rawTarget);
+  }
+
+  console.log(`Configured platforms: ${platforms.length > 0 ? platforms.join(', ') : '(single platform fallback)'}`);
+  if (useInbuild) {
+    console.log('ℹ️  Strategy: Built-in SBOM attestation extraction enabled (Docker Scout / Syft). Skips container layer downloads for maximum speed.');
+    console.log('ℹ️  Note: Built-in SBOM vulnerability counts may differ from direct filesystem scans (\'trivy image\') due to binary vs. source package tracking.');
+  } else {
+    console.log('ℹ️  Strategy: Direct Trivy image scanning enabled (default). Inspects full container rootfs and package databases for maximum fidelity.');
+  }
+
+  const targetPlatforms = platforms.length > 0 ? platforms : [''];
+
+  for (const platform of targetPlatforms) {
+    const archTag = toArchTag(platform);
+    // Head extraction
+    extractOrGenerateSbom({
+      image: headImage,
+      platform,
+      archTag,
+      outputDir: headDir,
+      useInbuild,
+    });
+    // Target extraction
+    extractOrGenerateSbom({
+      image: targetImage,
+      platform,
+      archTag,
+      outputDir: targetDir,
+      useInbuild,
+    });
+  }
+
+  // Collect generated files
+  const getSbomFiles = (dir) => {
+    if (!fs.existsSync(dir)) return [];
+    return fs.readdirSync(dir)
+      .filter((f) => f.startsWith('sbom-') && f.endsWith('.spdx.json'))
+      .map((f) => {
+        const fullPath = path.join(dir, f);
+        return { name: f, size: fs.statSync(fullPath).size };
+      });
+  };
+
+  const headFiles = getSbomFiles(headDir);
+  const targetFiles = getSbomFiles(targetDir);
+
+  let headError = null;
+  let targetError = null;
+  if (headFiles.length === 0) headError = 'No SBOM generated and head image could not be inspected';
+  if (targetFiles.length === 0) targetError = 'No SBOM generated and target baseline image could not be inspected';
+
+  const overview = formatSbomOverview({
+    headImage,
+    targetImage,
+    headFiles,
+    targetFiles,
+    headError,
+    targetError,
+  });
+  console.log(overview);
+
+  if (headError || targetError) {
+    console.error('::error::Both head and target images must have valid SBOMs to proceed with differential scanning.');
+    process.exit(1);
+  }
+
+  // Expose extracted head SBOMs to workspace root for workflow artifact uploads
+  for (const file of headFiles) {
+    try {
+      fs.copyFileSync(path.join(headDir, file.name), file.name);
+    } catch {
+      // Ignore copy error
+    }
+  }
+}
+
+if (require.main === module) {
+  main();
+}
+
+module.exports = {
+  parseArgs,
+  cleanupInvalidFile,
+  extractOrGenerateSbom,
+  main,
+};
diff --git a/lib/install-trivy.js b/lib/install-trivy.js
new file mode 100644
index 0000000..e3b06aa
--- /dev/null
+++ b/lib/install-trivy.js
@@ -0,0 +1,75 @@
+#!/usr/bin/env node
+
+/**
+ * Installs and verifies Trivy binary against checksums lockfile.
+ */
+
+const fs = require('node:fs');
+const path = require('node:path');
+const os = require('node:os');
+const cp = require('node:child_process');
+const { mapArch, parseChecksums, verifyFileSha256 } = require('./verifier.js');
+
+function main() {
+  const version = process.env.TRIVY_VERSION || '0.74.0';
+  const homeDir = os.homedir();
+  const binDir = path.join(homeDir, '.local', 'bin');
+  const cacheDir = path.join(homeDir, '.cache', 'trivy-bin');
+
+  fs.mkdirSync(binDir, { recursive: true });
+  fs.mkdirSync(cacheDir, { recursive: true });
+
+  // Expose bin directory to GITHUB_PATH if running in Actions runner
+  if (process.env.GITHUB_PATH) {
+    fs.appendFileSync(process.env.GITHUB_PATH, `${binDir}\n`);
+  }
+
+  const unameArch = os.arch() === 'x64' ? 'x86_64' : (os.arch() === 'arm64' ? 'ARM64' : os.arch());
+  const tArch = mapArch(unameArch);
+  const tarball = `trivy_${version}_Linux-${tArch}.tar.gz`;
+  const tarballPath = path.join(cacheDir, tarball);
+
+  const checksumsFile = path.resolve(__dirname, '..', 'checksums.txt');
+  if (!fs.existsSync(checksumsFile)) {
+    console.error(`::error::Checksums lockfile not found at ${checksumsFile}`);
+    process.exit(1);
+  }
+
+  const checksums = parseChecksums(fs.readFileSync(checksumsFile, 'utf8'));
+  const expectedHash = checksums.get(tarball);
+  if (!expectedHash) {
+    console.error(`::error::Tarball ${tarball} not found in checksums.txt`);
+    process.exit(1);
+  }
+
+  if (fs.existsSync(tarballPath) && verifyFileSha256(tarballPath, expectedHash)) {
+    console.log('Cached Trivy archive verified against lockfile.');
+  } else {
+    console.log('Archive missing or checksum mismatch; downloading...');
+    const downloadUrl = `https://github.com/aquasecurity/trivy/releases/download/v${version}/${tarball}`;
+    cp.execFileSync('curl', ['-sfLO', downloadUrl, '--output-dir', cacheDir], { stdio: 'inherit' });
+
+    if (!verifyFileSha256(tarballPath, expectedHash)) {
+      console.error(`::error::Downloaded archive ${tarball} failed SHA256 checksum verification!`);
+      process.exit(1);
+    }
+    console.log('Downloaded Trivy archive verified successfully.');
+  }
+
+  // Extract binary
+  cp.execFileSync('tar', ['-xzf', tarballPath, '-C', binDir, 'trivy'], { stdio: 'inherit' });
+  const trivyBin = path.join(binDir, 'trivy');
+  if (fs.existsSync(trivyBin)) {
+    fs.chmodSync(trivyBin, 0o755);
+    console.log(`Trivy ${version} installed and verified successfully at ${trivyBin}`);
+  } else {
+    console.error('::error::Failed to extract trivy binary from tarball.');
+    process.exit(1);
+  }
+}
+
+if (require.main === module) {
+  main();
+}
+
+module.exports = { main };
diff --git a/lib/platforms.js b/lib/platforms.js
new file mode 100644
index 0000000..2465df9
--- /dev/null
+++ b/lib/platforms.js
@@ -0,0 +1,54 @@
+/**
+ * Platform and architecture resolution utilities.
+ */
+
+function parsePlatforms(input) {
+  if (!input || typeof input !== 'string') return [];
+  const parts = input.split(',');
+  const platforms = [];
+  for (const part of parts) {
+    const clean = part.trim();
+    if (!clean) continue;
+    if (!clean.includes('/')) {
+      platforms.push(`linux/${clean}`);
+    } else {
+      platforms.push(clean);
+    }
+  }
+  return platforms;
+}
+
+function discoverPlatforms(headRawJson, targetRawJson) {
+  const set = new Set();
+  for (const raw of [headRawJson, targetRawJson]) {
+    if (!raw) continue;
+    try {
+      const data = JSON.parse(raw);
+      const manifests = data.manifests || [];
+      for (const m of manifests) {
+        if (m.platform && m.platform.architecture && m.platform.architecture !== 'unknown') {
+          const os = m.platform.os || 'linux';
+          const variant = m.platform.variant ? `/${m.platform.variant}` : '';
+          set.add(`${os}/${m.platform.architecture}${variant}`);
+        }
+      }
+    } catch {
+      // Ignore JSON parse errors from invalid manifests
+    }
+  }
+  return Array.from(set).sort();
+}
+
+function toArchTag(platform) {
+  if (!platform) return 'default';
+  // Strip optional leading os/ (e.g. linux/)
+  const withoutOs = platform.replace(/^[a-zA-Z0-9_-]+\//, '');
+  // Replace slashes with dashes (e.g. arm/v7 -> arm-v7)
+  return withoutOs.replace(/\//g, '-');
+}
+
+module.exports = {
+  parsePlatforms,
+  discoverPlatforms,
+  toArchTag,
+};
diff --git a/lib/scan-sboms.js b/lib/scan-sboms.js
new file mode 100644
index 0000000..2e4547c
--- /dev/null
+++ b/lib/scan-sboms.js
@@ -0,0 +1,280 @@
+#!/usr/bin/env node
+
+/**
+ * Scans multi-platform SBOMs with Trivy, handles distro detection and fallbacks,
+ * prints diagnostic overview, and invokes diff engine.
+ */
+
+const fs = require('node:fs');
+const path = require('node:path');
+const cp = require('node:child_process');
+const { detectDistro } = require('./distro.js');
+const { formatScanOverview, countVulnerabilities } = require('./diagnostics.js');
+
+function parseArgs(argv) {
+  const args = {
+    headImage: process.env.INPUT_HEAD_IMAGE || '',
+    targetImage: process.env.INPUT_TARGET_IMAGE || '',
+    targetBranch: process.env.INPUT_TARGET_BRANCH || 'main',
+    useInbuildSbom: process.env.INPUT_USE_INBUILD_SBOM || 'false',
+    outputDelta: process.env.INPUT_OUTPUT_DELTA || 'cve-delta.md',
+    outputSummary: process.env.INPUT_OUTPUT_SUMMARY || 'cve-summary.md',
+  };
+
+  for (let i = 2; i < argv.length; i++) {
+    const arg = argv[i];
+    if (arg === '--head-image' && i + 1 < argv.length) args.headImage = argv[++i];
+    else if (arg === '--target-image' && i + 1 < argv.length) args.targetImage = argv[++i];
+    else if (arg === '--target-branch' && i + 1 < argv.length) args.targetBranch = argv[++i];
+    else if (arg === '--use-inbuild-sbom' && i + 1 < argv.length) args.useInbuildSbom = argv[++i];
+    else if (arg === '--output-delta' && i + 1 < argv.length) args.outputDelta = argv[++i];
+    else if (arg === '--output-summary' && i + 1 < argv.length) args.outputSummary = argv[++i];
+  }
+
+  return args;
+}
+
+function scanSbomFile({ sbomPath, image, outJson, errLog, useInbuild }) {
+  const archMatch = path.basename(sbomPath, '.spdx.json').match(/^sbom-(.+)$/);
+  const arch = archMatch ? archMatch[1] : 'default';
+
+  console.log(`Scanning SBOM for architecture: ${arch}`);
+  let distroArg = [];
+  if (useInbuild) {
+    try {
+      const content = fs.readFileSync(sbomPath, 'utf8');
+      const detected = detectDistro(content);
+      if (detected) {
+        console.log(`Detected distribution '${detected}' from in-build SBOM PURLs. Scanning with --distro.`);
+        distroArg = ['--distro', detected];
+      }
+    } catch {
+      // Ignore read error
+    }
+  }
+
+  const runTrivySbom = () => {
+    try {
+      const errFd = fs.openSync(errLog, 'w');
+      try {
+        cp.execFileSync('trivy', [
+          'sbom',
+          ...distroArg,
+          '--skip-version-check',
+          '--format', 'json',
+          '--output', outJson,
+          sbomPath,
+        ], { stdio: ['ignore', 'ignore', errFd] });
+        return true;
+      } finally {
+        fs.closeSync(errFd);
+      }
+    } catch {
+      return false;
+    }
+  };
+
+  let scanSuccess = runTrivySbom();
+  let vulnCount = 0;
+  if (fs.existsSync(outJson) && fs.statSync(outJson).size > 0) {
+    vulnCount = countVulnerabilities(fs.readFileSync(outJson, 'utf8'));
+  }
+
+  // Fallback if in-build scan produced 0 findings or failed
+  if (useInbuild && (!scanSuccess || vulnCount === 0)) {
+    console.warn(`::warning::In-build SBOM for image (${arch}) yielded ${vulnCount} CVE findings. Falling back to direct Trivy image scan...`);
+    const platArgs = arch !== 'default' ? ['--platform', `linux/${arch}`] : [];
+    try {
+      cp.execFileSync('trivy', [
+        'image',
+        '--skip-version-check',
+        ...platArgs,
+        '--format', 'spdx-json',
+        '--output', sbomPath,
+        image,
+      ], { stdio: 'inherit' });
+
+      console.log('Re-scanning SBOM generated directly by Trivy...');
+      // Re-scan without external distroArg (Trivy's generated SBOM has OS declarations)
+      distroArg = [];
+      scanSuccess = runTrivySbom();
+      if (fs.existsSync(outJson) && fs.statSync(outJson).size > 0) {
+        vulnCount = countVulnerabilities(fs.readFileSync(outJson, 'utf8'));
+      }
+    } catch (e) {
+      console.warn(`::warning::Direct Trivy scan fallback failed for ${arch}: ${e.message}`);
+    }
+  }
+
+  return { arch, scanSuccess, vulnCount, outJson, errLog };
+}
+
+function main() {
+  const args = parseArgs(process.argv);
+  const {
+    headImage,
+    targetImage,
+    targetBranch,
+    useInbuildSbom,
+    outputDelta,
+    outputSummary,
+  } = args;
+  const useInbuild = useInbuildSbom === 'true';
+
+  fs.mkdirSync(path.join('cve-reports', 'head'), { recursive: true });
+  fs.mkdirSync(path.join('cve-reports', 'target'), { recursive: true });
+
+  const getSboms = (dir) => {
+    if (!fs.existsSync(dir)) return [];
+    return fs.readdirSync(dir)
+      .filter((f) => f.startsWith('sbom-') && f.endsWith('.spdx.json'))
+      .sort()
+      .map((f) => path.join(dir, f));
+  };
+
+  const headSboms = getSboms(path.join('sboms', 'head'));
+  const targetSboms = getSboms(path.join('sboms', 'target'));
+
+  let headOk = true;
+  let targetOk = true;
+  let headReportCount = 0;
+  let targetReportCount = 0;
+  const headSummary = [];
+  const targetSummary = [];
+
+  // 1. Scan Head SBOMs
+  if (headSboms.length === 0) {
+    headOk = false;
+    headSummary.push('  - ❌ No SBOM files found in sboms/head/');
+  } else {
+    for (const f of headSboms) {
+      const arch = path.basename(f, '.spdx.json').replace(/^sbom-/, '');
+      const outJson = path.join('cve-reports', 'head', `cve-${arch}.json`);
+      const errLog = path.join('cve-reports', 'head', `cve-${arch}.err`);
+
+      const res = scanSbomFile({
+        sbomPath: f,
+        image: headImage,
+        outJson,
+        errLog,
+        useInbuild,
+      });
+
+      if (res.scanSuccess && fs.existsSync(outJson) && fs.statSync(outJson).size > 0) {
+        if (res.vulnCount === 0) {
+          console.warn(`::warning::Head image architecture '${arch}' has 0 CVE findings. Verify that OS/packages were recognized.`);
+          headSummary.push(`  - ${arch}: ⚠️ WARNING (0 vulnerability findings detected)`);
+        } else {
+          headSummary.push(`  - ${arch}: ✅ OK (${res.vulnCount} vulnerability findings)`);
+        }
+        headReportCount++;
+      } else {
+        headOk = false;
+        let errMsg = 'Trivy scan exited with non-zero status';
+        if (fs.existsSync(errLog)) {
+          const errLines = fs.readFileSync(errLog, 'utf8').trim().split('\n');
+          errMsg = errLines.slice(-2).join(' ').replace(/\s+/g, ' ') || errMsg;
+        }
+        headSummary.push(`  - ${arch}: ❌ FAILED (${errMsg})`);
+      }
+    }
+  }
+
+  // 2. Scan Target SBOMs
+  if (targetSboms.length === 0) {
+    targetOk = false;
+    targetSummary.push('  - ❌ No SBOM files found in sboms/target/');
+  } else {
+    for (const f of targetSboms) {
+      const arch = path.basename(f, '.spdx.json').replace(/^sbom-/, '');
+      const outJson = path.join('cve-reports', 'target', `cve-${arch}.json`);
+      const errLog = path.join('cve-reports', 'target', `cve-${arch}.err`);
+
+      const res = scanSbomFile({
+        sbomPath: f,
+        image: targetImage,
+        outJson,
+        errLog,
+        useInbuild,
+      });
+
+      if (res.scanSuccess && fs.existsSync(outJson) && fs.statSync(outJson).size > 0) {
+        if (res.vulnCount === 0) {
+          console.warn(`::warning::Target baseline image architecture '${arch}' has 0 CVE findings. Verify that OS/packages were recognized.`);
+          targetSummary.push(`  - ${arch}: ⚠️ WARNING (0 vulnerability findings detected)`);
+        } else {
+          targetSummary.push(`  - ${arch}: ✅ OK (${res.vulnCount} vulnerability findings)`);
+        }
+        targetReportCount++;
+      } else {
+        targetOk = false;
+        let errMsg = 'Trivy scan exited with non-zero status';
+        if (fs.existsSync(errLog)) {
+          const errLines = fs.readFileSync(errLog, 'utf8').trim().split('\n');
+          errMsg = errLines.slice(-2).join(' ').replace(/\s+/g, ' ') || errMsg;
+        }
+        targetSummary.push(`  - ${arch}: ❌ FAILED (${errMsg})`);
+      }
+    }
+  }
+
+  // 3. Print Comprehensive Diagnostic Overview
+  const strategy = useInbuild
+    ? 'Built-in OCI Attestation (Syft/Docker Scout) with distro detection'
+    : 'Direct Trivy Image Scan (Full rootfs & source package mapping)';
+
+  const overview = formatScanOverview({
+    headImage,
+    targetImage,
+    targetBranch,
+    strategy,
+    headSummary,
+    targetSummary,
+  });
+  console.log(overview);
+
+  // 4. Enforce Gating
+  let hasError = false;
+  if (!headOk || headReportCount === 0) {
+    console.error('::error::Head image CVE analysis failed or produced no reports.');
+    hasError = true;
+  }
+  if (!targetOk || targetReportCount === 0) {
+    console.error('::error::Target baseline CVE analysis failed or produced no reports.');
+    hasError = true;
+  }
+
+  if (hasError) {
+    console.error('::error::Aborting differential analysis: both head and target scans must succeed before diffing.');
+    process.exit(1);
+  }
+
+  // 5. Run multi-arch set-based diff and generate reports
+  console.log('Both head and target scans succeeded. Computing set-based vulnerability delta...');
+  const cveDiffScript = path.resolve(__dirname, '..', 'cve-diff.js');
+  try {
+    const deltaOutput = cp.execFileSync(process.execPath, [
+      cveDiffScript,
+      path.join('cve-reports', 'target'),
+      path.join('cve-reports', 'head'),
+      targetBranch,
+      outputSummary,
+    ], { encoding: 'utf8' });
+
+    fs.writeFileSync(outputDelta, deltaOutput, 'utf8');
+    console.log(`CVE delta written to ${outputDelta} and full summary written to ${outputSummary}`);
+  } catch (e) {
+    console.error(`::error::Failed to generate CVE differential report: ${e.message}`);
+    process.exit(1);
+  }
+}
+
+if (require.main === module) {
+  main();
+}
+
+module.exports = {
+  parseArgs,
+  scanSbomFile,
+  main,
+};
diff --git a/lib/verifier.js b/lib/verifier.js
new file mode 100644
index 0000000..d3182d4
--- /dev/null
+++ b/lib/verifier.js
@@ -0,0 +1,56 @@
+/**
+ * Architecture mapping and cryptographic checksum verification.
+ */
+
+const fs = require('node:fs');
+const crypto = require('node:crypto');
+
+function mapArch(unameArch) {
+  const normalized = (unameArch || '').trim().toLowerCase();
+  switch (normalized) {
+    case 'x86_64':
+    case 'amd64':
+      return '64bit';
+    case 'aarch64':
+    case 'arm64':
+      return 'ARM64';
+    default:
+      throw new Error(`Unsupported architecture: ${unameArch}`);
+  }
+}
+
+function parseChecksums(checksumsContent) {
+  const map = new Map();
+  if (!checksumsContent) return map;
+
+  const lines = checksumsContent.split(/\r?\n/);
+  for (const line of lines) {
+    const trimmed = line.trim();
+    if (!trimmed || trimmed.startsWith('#')) continue;
+    // Format: <hash>  <filename>
+    const match = trimmed.match(/^([a-fA-F0-9]{64})\s+(.+)$/);
+    if (match) {
+      const hash = match[1].toLowerCase();
+      const filename = match[2].trim();
+      map.set(filename, hash);
+    }
+  }
+  return map;
+}
+
+function verifyFileSha256(filePath, expectedHash) {
+  if (!fs.existsSync(filePath) || !expectedHash) return false;
+  try {
+    const fileBuffer = fs.readFileSync(filePath);
+    const actualHash = crypto.createHash('sha256').update(fileBuffer).digest('hex');
+    return actualHash.toLowerCase() === expectedHash.toLowerCase();
+  } catch {
+    return false;
+  }
+}
+
+module.exports = {
+  mapArch,
+  parseChecksums,
+  verifyFileSha256,
+};
diff --git a/test/diagnostics.test.js b/test/diagnostics.test.js
new file mode 100644
index 0000000..b8a97e4
--- /dev/null
+++ b/test/diagnostics.test.js
@@ -0,0 +1,76 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const {
+  formatSbomOverview,
+  formatScanOverview,
+  countVulnerabilities,
+} = require('../lib/diagnostics.js');
+
+test('formatSbomOverview formats successful extraction banner', () => {
+  const overview = formatSbomOverview({
+    headImage: 'my-head:latest',
+    targetImage: 'my-target:latest',
+    headFiles: [{ name: 'sbom-amd64.spdx.json', size: 1024 }],
+    targetFiles: [{ name: 'sbom-amd64.spdx.json', size: 2048 }],
+    headError: null,
+    targetError: null,
+  });
+
+  assert.ok(overview.includes('SBOM EXTRACTION DIAGNOSTIC OVERVIEW'));
+  assert.ok(overview.includes('HEAD Image (my-head:latest): ✅ SUCCESS'));
+  assert.ok(overview.includes('TARGET Baseline Image (my-target:latest): ✅ SUCCESS'));
+  assert.ok(overview.includes('sbom-amd64.spdx.json (1024 bytes)'));
+});
+
+test('formatSbomOverview formats failure banner when error present', () => {
+  const overview = formatSbomOverview({
+    headImage: 'my-head:latest',
+    targetImage: 'my-target:latest',
+    headFiles: [],
+    targetFiles: [],
+    headError: 'Image not found',
+    targetError: null,
+  });
+
+  assert.ok(overview.includes('HEAD Image (my-head:latest): ❌ FAILED - Image not found'));
+});
+
+test('formatScanOverview formats scan summary with strategy', () => {
+  const overview = formatScanOverview({
+    headImage: 'debian:bookworm-slim',
+    targetImage: 'debian:bullseye-slim',
+    targetBranch: 'main',
+    strategy: 'Direct Trivy Image Scan',
+    headSummary: ['  - amd64: ✅ OK (104 vulnerability findings)'],
+    targetSummary: ['  - amd64: ✅ OK (130 vulnerability findings)'],
+  });
+
+  assert.ok(overview.includes('CVE VULNERABILITY SCAN DIAGNOSTIC OVERVIEW'));
+  assert.ok(overview.includes('Scan Strategy: Direct Trivy Image Scan'));
+  assert.ok(overview.includes('HEAD Image: debian:bookworm-slim'));
+  assert.ok(overview.includes('TARGET Baseline Image: debian:bullseye-slim (branch: \'main\')'));
+  assert.ok(overview.includes('104 vulnerability findings'));
+});
+
+test('countVulnerabilities counts all vulnerabilities in a Trivy JSON report', () => {
+  const report = {
+    Results: [
+      {
+        Vulnerabilities: [
+          { VulnerabilityID: 'CVE-2023-0001' },
+          { VulnerabilityID: 'CVE-2023-0002' },
+        ],
+      },
+      {
+        Vulnerabilities: [
+          { VulnerabilityID: 'CVE-2023-0003' },
+        ],
+      },
+    ],
+  };
+
+  assert.equal(countVulnerabilities(report), 3);
+  assert.equal(countVulnerabilities(JSON.stringify(report)), 3);
+  assert.equal(countVulnerabilities({}), 0);
+  assert.equal(countVulnerabilities(null), 0);
+});
diff --git a/test/distro.test.js b/test/distro.test.js
new file mode 100644
index 0000000..bd7952b
--- /dev/null
+++ b/test/distro.test.js
@@ -0,0 +1,81 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const { detectDistro } = require('../lib/distro.js');
+
+test('detectDistro returns null for null, undefined, or empty input', () => {
+  assert.equal(detectDistro(null), null);
+  assert.equal(detectDistro(undefined), null);
+  assert.equal(detectDistro(''), null);
+  assert.equal(detectDistro('{}'), null);
+});
+
+test('detectDistro extracts distro from parsed SPDX object with package PURLs', () => {
+  const spdx = {
+    packages: [
+      {
+        name: 'acl',
+        externalRefs: [
+          {
+            referenceType: 'purl',
+            referenceLocator: 'pkg:deb/debian/acl@2.3.1-3?os_distro=bookworm&os_name=debian&os_version=12',
+          },
+        ],
+      },
+    ],
+  };
+
+  assert.equal(detectDistro(spdx), 'debian/12');
+});
+
+test('detectDistro extracts distro from JSON string containing escaped unicode \\u0026', () => {
+  const jsonStr = JSON.stringify({
+    packages: [
+      {
+        name: 'adduser',
+        externalRefs: [
+          {
+            referenceType: 'purl',
+            referenceLocator: 'pkg:deb/debian/adduser@3.134?os_distro=bullseye&os_name=debian&os_version=11',
+          },
+        ],
+      },
+    ],
+  }).replace(/&/g, '\\u0026');
+
+  assert.ok(jsonStr.includes('\\u0026'));
+  assert.equal(detectDistro(jsonStr), 'debian/11');
+});
+
+test('detectDistro handles non-debian distributions (e.g. ubuntu, alpine)', () => {
+  const spdx = {
+    packages: [
+      {
+        externalRefs: [
+          {
+            referenceType: 'purl',
+            referenceLocator: 'pkg:apk/alpine/alpine-baselayout@3.4.3-r2?os_name=alpine&os_version=3.20',
+          },
+        ],
+      },
+    ],
+  };
+
+  assert.equal(detectDistro(spdx), 'alpine/3.20');
+});
+
+test('detectDistro returns null when PURLs lack os_name or os_version', () => {
+  const spdx = {
+    packages: [
+      {
+        externalRefs: [
+          {
+            referenceType: 'purl',
+            referenceLocator: 'pkg:generic/foo@1.0.0',
+          },
+        ],
+      },
+    ],
+  };
+
+  assert.equal(detectDistro(spdx), null);
+});
diff --git a/test/orchestration.test.js b/test/orchestration.test.js
new file mode 100644
index 0000000..10668b0
--- /dev/null
+++ b/test/orchestration.test.js
@@ -0,0 +1,65 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const os = require('node:os');
+const { parseArgs: parseExtractArgs, cleanupInvalidFile } = require('../lib/extract-sboms.js');
+const { parseArgs: parseScanArgs } = require('../lib/scan-sboms.js');
+
+test('extract-sboms parseArgs parses command line arguments and defaults', () => {
+  const argv = [
+    'node',
+    'extract-sboms.js',
+    '--head-image', 'my-repo/head:1.0',
+    '--target-image', 'my-repo/target:1.0',
+    '--architectures', 'amd64,arm64',
+    '--use-inbuild-sbom', 'true',
+  ];
+
+  const args = parseExtractArgs(argv);
+  assert.equal(args.headImage, 'my-repo/head:1.0');
+  assert.equal(args.targetImage, 'my-repo/target:1.0');
+  assert.equal(args.architectures, 'amd64,arm64');
+  assert.equal(args.useInbuildSbom, 'true');
+});
+
+test('extract-sboms cleanupInvalidFile removes empty files and files containing null', () => {
+  const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'sbom-clean-'));
+  const emptyFile = path.join(tmpDir, 'empty.json');
+  const nullFile = path.join(tmpDir, 'null.json');
+  const validFile = path.join(tmpDir, 'valid.json');
+
+  fs.writeFileSync(emptyFile, '');
+  fs.writeFileSync(nullFile, 'null\n');
+  fs.writeFileSync(validFile, '{"spdxVersion": "SPDX-2.3"}');
+
+  cleanupInvalidFile(emptyFile);
+  cleanupInvalidFile(nullFile);
+  cleanupInvalidFile(validFile);
+
+  assert.equal(fs.existsSync(emptyFile), false);
+  assert.equal(fs.existsSync(nullFile), false);
+  assert.equal(fs.existsSync(validFile), true);
+
+  fs.rmSync(tmpDir, { recursive: true, force: true });
+});
+
+test('scan-sboms parseArgs parses scan arguments and defaults', () => {
+  const argv = [
+    'node',
+    'scan-sboms.js',
+    '--head-image', 'my-head:latest',
+    '--target-image', 'my-target:latest',
+    '--target-branch', 'feature',
+    '--output-delta', 'custom-delta.md',
+    '--output-summary', 'custom-summary.md',
+  ];
+
+  const args = parseScanArgs(argv);
+  assert.equal(args.headImage, 'my-head:latest');
+  assert.equal(args.targetImage, 'my-target:latest');
+  assert.equal(args.targetBranch, 'feature');
+  assert.equal(args.outputDelta, 'custom-delta.md');
+  assert.equal(args.outputSummary, 'custom-summary.md');
+  assert.equal(args.useInbuildSbom, 'false');
+});
diff --git a/test/platforms.test.js b/test/platforms.test.js
new file mode 100644
index 0000000..ead5bce
--- /dev/null
+++ b/test/platforms.test.js
@@ -0,0 +1,47 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const { parsePlatforms, discoverPlatforms, toArchTag } = require('../lib/platforms.js');
+
+test('parsePlatforms handles empty and undefined input', () => {
+  assert.deepEqual(parsePlatforms(''), []);
+  assert.deepEqual(parsePlatforms(null), []);
+  assert.deepEqual(parsePlatforms(undefined), []);
+  assert.deepEqual(parsePlatforms('   '), []);
+});
+
+test('parsePlatforms parses comma-separated architectures and adds linux/ prefix if omitted', () => {
+  const result = parsePlatforms('amd64, arm64, linux/arm/v7');
+  assert.deepEqual(result, ['linux/amd64', 'linux/arm64', 'linux/arm/v7']);
+});
+
+test('discoverPlatforms extracts unique architectures from OCI image manifests', () => {
+  const headManifest = JSON.stringify({
+    manifests: [
+      { platform: { architecture: 'amd64', os: 'linux' } },
+      { platform: { architecture: 'arm64', os: 'linux' } },
+      { platform: { architecture: 'unknown', os: 'unknown' } },
+    ],
+  });
+
+  const targetManifest = JSON.stringify({
+    manifests: [
+      { platform: { architecture: 'amd64', os: 'linux' } },
+      { platform: { architecture: 'arm', os: 'linux', variant: 'v7' } },
+    ],
+  });
+
+  const result = discoverPlatforms(headManifest, targetManifest);
+  assert.deepEqual(result, ['linux/amd64', 'linux/arm/v7', 'linux/arm64']);
+});
+
+test('discoverPlatforms safely handles invalid or missing manifest JSON', () => {
+  assert.deepEqual(discoverPlatforms('invalid json', null), []);
+  assert.deepEqual(discoverPlatforms('', '{}'), []);
+});
+
+test('toArchTag converts platform strings to filesystem-safe arch tags', () => {
+  assert.equal(toArchTag('linux/amd64'), 'amd64');
+  assert.equal(toArchTag('linux/arm64'), 'arm64');
+  assert.equal(toArchTag('linux/arm/v7'), 'arm-v7');
+  assert.equal(toArchTag('amd64'), 'amd64');
+});
diff --git a/test/verifier.test.js b/test/verifier.test.js
new file mode 100644
index 0000000..1bccc1e
--- /dev/null
+++ b/test/verifier.test.js
@@ -0,0 +1,39 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const os = require('node:os');
+const crypto = require('node:crypto');
+const { mapArch, parseChecksums, verifyFileSha256 } = require('../lib/verifier.js');
+
+test('mapArch maps uname architecture to Trivy release arch', () => {
+  assert.equal(mapArch('x86_64'), '64bit');
+  assert.equal(mapArch('aarch64'), 'ARM64');
+  assert.equal(mapArch('arm64'), 'ARM64');
+  assert.throws(() => mapArch('mips'), /Unsupported architecture/);
+});
+
+test('parseChecksums parses sha256 checksum lockfile into filename map', () => {
+  const content = `
+    e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855  trivy_0.74.0_Linux-64bit.tar.gz
+    a1b2c3d4e5f60000000000000000000000000000000000000000000000000000  trivy_0.74.0_Linux-ARM64.tar.gz
+  `;
+
+  const map = parseChecksums(content);
+  assert.equal(map.get('trivy_0.74.0_Linux-64bit.tar.gz'), 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855');
+  assert.equal(map.get('trivy_0.74.0_Linux-ARM64.tar.gz'), 'a1b2c3d4e5f60000000000000000000000000000000000000000000000000000');
+  assert.equal(map.has('nonexistent'), false);
+});
+
+test('verifyFileSha256 verifies actual sha256 hash of a file', () => {
+  const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'cve-test-'));
+  const testFile = path.join(tmpDir, 'test.txt');
+  const fileContent = 'hello world\n';
+  fs.writeFileSync(testFile, fileContent);
+
+  const expectedHash = crypto.createHash('sha256').update(fileContent).digest('hex');
+  assert.equal(verifyFileSha256(testFile, expectedHash), true);
+  assert.equal(verifyFileSha256(testFile, 'wronghash'), false);
+
+  fs.rmSync(tmpDir, { recursive: true, force: true });
+});