diff --git a/.github/workflows/healthchat-release-playstore.yml b/.github/workflows/healthchat-release-playstore.yml
index 734ff52ba9..561313cc55 100644
--- a/.github/workflows/healthchat-release-playstore.yml
+++ b/.github/workflows/healthchat-release-playstore.yml
@@ -65,7 +65,7 @@ jobs:
     # "The operation was canceled" and no other diagnostic.
     runs-on: [self-hosted, Linux, X64]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4.4.0
         with:
           fetch-depth: 0
           persist-credentials: false
@@ -85,10 +85,13 @@ jobs:
 
       - name: Resolve marketing version
         id: version
+        env:
+          # Passed through the environment, never expanded into the script (zizmor: template-injection).
+          INPUT_VERSION: ${{ github.event.inputs.version }}
         run: |
           set -euo pipefail
-          if [[ "${{ github.event_name }}" == "workflow_dispatch" ]]; then
-            VERSION="${{ github.event.inputs.version }}"
+          if [[ "$GITHUB_EVENT_NAME" == "workflow_dispatch" ]]; then
+            VERSION="$INPUT_VERSION"
           else
             VERSION="${GITHUB_REF_NAME#healthchat-v}"
           fi
@@ -178,7 +181,7 @@ jobs:
           done
 
       - name: Use JDK 21
-        uses: actions/setup-java@v4
+        uses: actions/setup-java@cf277c60eb25467037889841efdb72551f06f6c3 # v4.9.1
         with:
           distribution: 'temurin'
           java-version: '21'
@@ -192,7 +195,10 @@ jobs:
       # (SdkConstants.CURRENT_BUILD_TOOLS_VERSION), since nothing sets buildToolsVersion
       # here. Both need refreshing in the image when AGP or COMPILE_SDK moves.
       - name: Configure gradle
-        uses: gradle/actions/setup-gradle@v4
+        uses: gradle/actions/setup-gradle@748248ddd2a24f49513d8f472f81c3a07d4d50e1 # v4.4.4
+        with:
+          # Release builds must not consume a cache another workflow could have poisoned.
+          cache-disabled: true
 
       - name: Decode keystore
         run: |
@@ -222,7 +228,7 @@ jobs:
 
       - name: Upload workflow artifacts
         if: always()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: healthchat-${{ steps.version.outputs.version }}
           path: |
@@ -232,7 +238,7 @@ jobs:
           if-no-files-found: warn
 
       - name: Upload to Play Store
-        uses: r0adkll/upload-google-play@v1
+        uses: r0adkll/upload-google-play@e738b9dd8f2476ea806d921b64aacd24f34515a5 # v1.1.5
         with:
           serviceAccountJsonPlainText: ${{ secrets.GOOGLE_PLAY_SERVICE_ACCOUNT_JSON }}
           packageName: ch.healthchat.element