diff --git a/.github/actions/bootstrap/action.yaml b/.github/actions/bootstrap/action.yaml
index 67717b789..eb2b126b5 100644
--- a/.github/actions/bootstrap/action.yaml
+++ b/.github/actions/bootstrap/action.yaml
@@ -49,8 +49,17 @@ runs:
         IFS=' ' read -ra packages <<< "$APT_PACKAGES"
         DEBIAN_FRONTEND=noninteractive sudo apt update && sudo -E apt install -y "${packages[@]}"
 
+    # ORAS cache: restore-only on non-default branches / forks
     - name: Restore ORAS cache from github actions
-      if: inputs.download-test-fixture-cache == 'true'
+      if: ${{ inputs.download-test-fixture-cache == 'true' && (github.ref != format('refs/heads/{0}', github.event.repository.default_branch) || github.event.repository.fork == true) }}
+      uses: actions/cache/restore@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5.0.5
+      with:
+        path: ${{ github.workspace }}/.tmp/oras-cache
+        key: ${{ inputs.cache-key-prefix }}-oras-cache
+
+    # ORAS cache: restore + save on the default branch of the canonical repo only.
+    - name: Restore and save ORAS cache from github actions
+      if: ${{ inputs.download-test-fixture-cache == 'true' && github.ref == format('refs/heads/{0}', github.event.repository.default_branch) && github.event.repository.fork == false }}
       uses: actions/cache@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5.0.5
       with:
         path: ${{ github.workspace }}/.tmp/oras-cache
diff --git a/.github/workflows/release.yaml b/.github/workflows/release.yaml
index 9792debc7..2d40b1250 100644
--- a/.github/workflows/release.yaml
+++ b/.github/workflows/release.yaml
@@ -101,26 +101,6 @@ jobs:
           file: go.mod
           artifact-name: sbom.spdx.json
 
-      - name: Notify Slack of new release
-        uses: slackapi/slack-github-action@45a88b9581bfab2566dc881e2cd66d334e621e2c #v3.0.3
-        continue-on-error: true
-        with:
-          webhook: ${{ secrets.SLACK_TOOLBOX_WEBHOOK_URL }}
-          webhook-type: incoming-webhook
-          payload: |
-            text: "A new Syft release has been published: https://github.com/anchore/syft/releases/tag/${{ github.event.inputs.version }}"
-            blocks:
-              - type: section
-                text:
-                  type: mrkdwn
-                  text: |
-                    *A new Syft release has been published* :rocket:
-                    • Release: <https://github.com/anchore/syft/releases/tag/${{ github.event.inputs.version }}|${{ github.event.inputs.version }}>
-                    • Repo: `${{ github.repository }}`
-                    • Workflow: `${{ github.workflow }}`
-                    • Event: `${{ github.event_name }}`
-        if: ${{ success() }}
-
   release-install-script:
     needs: [release]
     if: ${{ always() && (needs.release.result == 'success' || github.event.inputs.phase == 'install-script-only') }}
diff --git a/.github/workflows/validations.yaml b/.github/workflows/validations.yaml
index 9eac05f69..f44181164 100644
--- a/.github/workflows/validations.yaml
+++ b/.github/workflows/validations.yaml
@@ -21,9 +21,10 @@ jobs:
     name: "Static analysis"
     # runs-on.com: memory & general purpose instances for testing
     #   spot enabled: ok to interrupt non-production workloads
-    #   s3-cache: faster actions cache
     #   tmpfs: faster io-intensive workflows
-    runs-on: &test-runner "runs-on=${{ github.run_id }}/cpu=4+8/ram=32+128/family=r5+r6+r7+r8+m4+m5+m6+m7+m8/spot=price-capacity-optimized/extras=s3-cache+tmpfs"
+    #   note: s3-cache intentionally omitted -- PR runs are untrusted and must not write to the
+    #   shared cache backend that the trusted release workflow reads from (cache poisoning).
+    runs-on: &test-runner "runs-on=${{ github.run_id }}/cpu=4+8/ram=32+128/family=r5+r6+r7+r8+m4+m5+m6+m7+m8/spot=price-capacity-optimized/extras=tmpfs"
     permissions:
       contents: read
     steps:
@@ -91,15 +92,13 @@ jobs:
     # runs-on.com: compute instances for parallel builds
     #   spot disabled: reliability for build workflows (used for releases too)
     #   goreleaser uses parallelism of 12, so we need more CPUs
-    #   s3-cache: faster actions cache
     #   tmpfs: faster io-intensive workflows
-    runs-on: "runs-on=${{ github.run_id }}/cpu=16+32/ram=32+128/family=c5+c6+c7+c8/spot=false/extras=s3-cache+tmpfs"
+    #   note: s3-cache intentionally omitted -- PR runs are untrusted and must not write to the
+    #   shared cache backend that the trusted release workflow reads from (cache poisoning).
+    runs-on: "runs-on=${{ github.run_id }}/cpu=16+32/ram=32+128/family=c5+c6+c7+c8/spot=false/extras=tmpfs"
     permissions:
       contents: read
     steps:
-      # required for magic-cache from runs-on to function with artifact upload/download (see https://runs-on.com/caching/magic-cache/#actionsupload-artifact-compatibility)
-      - uses: runs-on/action@d141ef83eb66d096ce8afc767e09115a65c63b60  # v2.1.2
-
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd #v6.0.2
         with:
           persist-credentials: false
@@ -130,9 +129,6 @@ jobs:
     permissions:
       contents: read
     steps:
-      # required for magic-cache from runs-on to function with artifact upload/download (see https://runs-on.com/caching/magic-cache/#actionsupload-artifact-compatibility)
-      - uses: runs-on/action@d141ef83eb66d096ce8afc767e09115a65c63b60  # v2.1.2
-
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd #v6.0.2
         with:
           persist-credentials: false
@@ -211,9 +207,6 @@ jobs:
     permissions:
       contents: read
     steps:
-      # required for magic-cache from runs-on to function with artifact upload/download (see https://runs-on.com/caching/magic-cache/#actionsupload-artifact-compatibility)
-      - uses: runs-on/action@d141ef83eb66d096ce8afc767e09115a65c63b60  # v2.1.2
-
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd #v6.0.2
         with:
           persist-credentials: false