diff --git a/.github/workflows/agda.yml b/.github/workflows/agda.yml
index e1e55ee..be93f69 100644
--- a/.github/workflows/agda.yml
+++ b/.github/workflows/agda.yml
@@ -35,7 +35,7 @@ jobs:
     timeout-minutes: 30
     steps:
       - name: Checkout
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
 
       # Fast static gate (no Agda): enforce the EchoKernel funext-free
       # certificate and that every Echo*.agda is classified in
@@ -121,7 +121,7 @@ jobs:
       # source change or absolute-zero bump; restore-keys give a warm
       # partial cache even when it does.
       - name: Cache Agda interface files
-        uses: actions/cache@v6.1.0
+        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9  # v6.1.0
         with:
           path: |
             ~/agda-stdlib/**/*.agdai
@@ -167,7 +167,7 @@ jobs:
     timeout-minutes: 30
     steps:
       - name: Checkout
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
 
       - name: Install Agda
         run: |
diff --git a/.github/workflows/codeql.yml b/.github/workflows/codeql.yml
index e0b966c..ab7e6a7 100644
--- a/.github/workflows/codeql.yml
+++ b/.github/workflows/codeql.yml
@@ -43,15 +43,15 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
 
       - name: Initialize CodeQL
-        uses: github/codeql-action/init@v4.38.0
+        uses: github/codeql-action/init@b96794f015dfd88f77b49b1c93e0fa7110f94c63  # v4.38.0
         with:
           languages: ${{ matrix.language }}
           build-mode: ${{ matrix.build-mode }}
 
       - name: Perform CodeQL Analysis
-        uses: github/codeql-action/analyze@v4.38.0
+        uses: github/codeql-action/analyze@b96794f015dfd88f77b49b1c93e0fa7110f94c63  # v4.38.0
         with:
           category: "/language:${{ matrix.language }}"
diff --git a/.github/workflows/hypatia-scan.yml b/.github/workflows/hypatia-scan.yml
index 61bccb9..3fe4d49 100644
--- a/.github/workflows/hypatia-scan.yml
+++ b/.github/workflows/hypatia-scan.yml
@@ -51,12 +51,12 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
         with:
           fetch-depth: 0  # Full history for better pattern analysis
 
       - name: Setup Elixir for Hypatia scanner
-        uses: erlef/setup-beam@v1.24.1
+        uses: erlef/setup-beam@54075bcc5e249e4758d363f27d099f55d843f124  # v1.24.1
         with:
           elixir-version: '1.18'
           otp-version: '27'
@@ -110,7 +110,7 @@ jobs:
           echo "- Medium: $MEDIUM" >> $GITHUB_STEP_SUMMARY
 
       - name: Upload findings artifact
-        uses: actions/upload-artifact@v7.0.1
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a  # v7.0.1
         with:
           name: hypatia-findings
           path: hypatia-findings.json
@@ -246,7 +246,7 @@ jobs:
           always() &&
           (github.event_name != 'pull_request' ||
            github.event.pull_request.head.repo.fork != true)
-        uses: github/codeql-action/upload-sarif@v4.38.0
+        uses: github/codeql-action/upload-sarif@b96794f015dfd88f77b49b1c93e0fa7110f94c63  # v4.38.0
         with:
           sarif_file: hypatia.sarif
           # Distinct category so Hypatia results coexist with CodeQL's
@@ -386,7 +386,7 @@ jobs:
         # the pull-requests: write permission above: a token/API hiccup or
         # a fork PR (read-only token) skips the comment, not the check.
         continue-on-error: true
-        uses: actions/github-script@v9.0.0
+        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3  # v9.0.0
         with:
           script: |
             const fs = require('fs');
diff --git a/.github/workflows/pages.yml b/.github/workflows/pages.yml
index 4124e83..5962921 100644
--- a/.github/workflows/pages.yml
+++ b/.github/workflows/pages.yml
@@ -21,9 +21,9 @@ jobs:
       image: ghcr.io/stefan-hoeck/idris2-pack@sha256:f0758996a931fb35d9ecb1de273c4d59dabe2a09b433afc7e357f65a08b7e1ff
     steps:
       - name: Checkout Site
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
       - name: Checkout Ddraig SSG
-        uses: actions/checkout@v7.0.1
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
         with:
           repository: hyperpolymath/ddraig-ssg
           path: .ddraig-ssg
@@ -40,7 +40,7 @@ jobs:
           fi
           ./.ddraig-ssg/build/exec/ddraig build src _site https://hyperpolymath.github.io/${GITHUB_REPOSITORY#*/}
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v5.0.0
+        uses: actions/upload-pages-artifact@fc324d3547104276b827a68afc52ff2a11cc49c9  # v5.0.0
         with:
           path: '_site'
   deploy:
@@ -53,4 +53,4 @@ jobs:
     steps:
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v5.0.1
+        uses: actions/deploy-pages@368f82528645a54fb793d4d04e342629a3f51346  # v5.0.1
diff --git a/.github/workflows/push-email-notify.yml b/.github/workflows/push-email-notify.yml
index 8d1f093..521f1e5 100644
--- a/.github/workflows/push-email-notify.yml
+++ b/.github/workflows/push-email-notify.yml
@@ -40,7 +40,7 @@ jobs:
     timeout-minutes: 5
     steps:
       - name: Send push notification email
-        uses: hyperpolymath/smtp-notify-action@v0.3.0 # NOSONAR — pin authority is actions.lock (sha1-ede1191ef6ff3ac02c4f4d9efdf837ee517e11d7)
+        uses: hyperpolymath/smtp-notify-action@22e7bdb322c430c1d0dac6b3bb307f4bb139d0be  # NOSONAR — pin authority is actions.lock (sha1-ede1191ef6ff3ac02c4f4d9efdf837ee517e11d7)
         with:
           server_address: ${{ secrets.SMTP_HOST }}
           server_port: ${{ secrets.SMTP_PORT }}