diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index 2d6a7bff63e..0e437ab0320 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -22,9 +22,12 @@ updates:
       default-days: 1
 
   # Tracks the digest-pinned `COPY --from` image (ghcr.io/astral-sh/uv) in
-  # docker/Dockerfile.base. Note: the python:3.12-slim base/builder images are
-  # passed via build args from docker/docker-bake.hcl and the `docker run` image
-  # strings in workflows are not parsed by Dependabot; bump those manually.
+  # docker/Dockerfile.base. Note: the python:3.12-slim base/builder digests are
+  # carried both as the build_image/base_image ARG defaults in Dockerfile.base
+  # and in docker/docker-bake.hcl (which overrides them at build time).
+  # Dependabot does NOT parse images that reach FROM via an ARG, nor the
+  # `docker run` image strings in workflows, so bump those by hand and keep the
+  # Dockerfile.base ARG defaults and docker-bake.hcl digests in sync.
   - package-ecosystem: 'docker'
     directory: '/docker'
     schedule:
diff --git a/.github/workflows/codeql.yml b/.github/workflows/codeql.yml
new file mode 100644
index 00000000000..fabd9edb146
--- /dev/null
+++ b/.github/workflows/codeql.yml
@@ -0,0 +1,56 @@
+name: CodeQL
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+# Cancel a superseded run for the same ref (e.g. a force-push to a PR) so we
+# don't burn CI minutes analyzing commits that are already stale.
+concurrency:
+  group: codeql-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  analyze:
+    name: Analyze (${{ matrix.language }})
+    runs-on: ubuntu-latest
+    timeout-minutes: 360
+    permissions:
+      # Required to upload code-scanning results to the Security tab.
+      security-events: write
+      # Required by codeql-action to read the workflow/CI config.
+      actions: read
+      contents: read
+
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          # Haystack is a Python project; Python is interpreted, so no build is
+          # needed. Add `javascript-typescript` here if the docs-website JS code
+          # should also be scanned.
+          - language: python
+            build-mode: none
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@dd903d2e4f5405488e5ef1422510ee31c8b32357 # v3.36.2
+        with:
+          languages: ${{ matrix.language }}
+          build-mode: ${{ matrix.build-mode }}
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@dd903d2e4f5405488e5ef1422510ee31c8b32357 # v3.36.2
+        with:
+          category: "/language:${{ matrix.language }}"
diff --git a/.github/workflows/docs_search_sync.yml b/.github/workflows/docs_search_sync.yml
index d34f32c750a..67511f34d0c 100644
--- a/.github/workflows/docs_search_sync.yml
+++ b/.github/workflows/docs_search_sync.yml
@@ -36,7 +36,7 @@ jobs:
       - name: Install Docusaurus and build docs-website
         working-directory: docs-website
         run: |
-          npm install --ignore-scripts
+          npm ci --ignore-scripts
           npm rebuild sharp
           npm run build
 
diff --git a/.github/workflows/scorecard.yml b/.github/workflows/scorecard.yml
index f15945931d4..fd9761cae1a 100644
--- a/.github/workflows/scorecard.yml
+++ b/.github/workflows/scorecard.yml
@@ -61,6 +61,6 @@ jobs:
           retention-days: 5
 
       - name: Upload to code-scanning
-        uses: github/codeql-action/upload-sarif@662472033e021d55d94146f66f6058822b0b39fd # v3.27.0
+        uses: github/codeql-action/upload-sarif@dd903d2e4f5405488e5ef1422510ee31c8b32357 # v3.36.2
         with:
           sarif_file: results.sarif
diff --git a/.github/workflows/workflows_linting.yml b/.github/workflows/workflows_linting.yml
index 9801257050f..16bb61e0eca 100644
--- a/.github/workflows/workflows_linting.yml
+++ b/.github/workflows/workflows_linting.yml
@@ -22,7 +22,7 @@ jobs:
           go-version: ">=1.24.0"
 
       - name: Install actionlint
-        run: go install github.com/rhysd/actionlint/cmd/actionlint@latest
+        run: go install github.com/rhysd/actionlint/cmd/actionlint@v1.7.12
 
       - name: Run actionlint
         env:
diff --git a/docker/Dockerfile.base b/docker/Dockerfile.base
index e3de37c8a8f..c4cee03a765 100644
--- a/docker/Dockerfile.base
+++ b/docker/Dockerfile.base
@@ -1,7 +1,10 @@
-ARG build_image
-ARG base_image
+# Pinned digest defaults so the base images are resolvable by hash even when
+# the args are not passed (e.g. by supply-chain scanners or a plain `docker build`).
+# docker/docker-bake.hcl overrides these at build time; keep the digests in sync.
+ARG build_image=python:3.12-slim@sha256:090ba77e2958f6af52a5341f788b50b032dd4ca28377d2893dcf1ecbdfdfe203
+ARG base_image=python:3.12-slim@sha256:090ba77e2958f6af52a5341f788b50b032dd4ca28377d2893dcf1ecbdfdfe203
 
-FROM $build_image AS build-image
+FROM ${build_image} AS build-image
 
 ARG DEBIAN_FRONTEND=noninteractive
 ARG haystack_version
@@ -25,7 +28,7 @@ ENV PATH="/opt/venv/bin:$PATH"
 RUN uv pip install --no-cache-dir -U setuptools && \
     uv pip install --no-cache-dir .
 
-FROM $base_image AS final
+FROM ${base_image} AS final
 
 COPY --from=build-image /opt/venv /opt/venv