diff --git a/.github/workflows/benchmark.yml b/.github/workflows/benchmark.yml
index 0c4ab71..fa5dd5c 100644
--- a/.github/workflows/benchmark.yml
+++ b/.github/workflows/benchmark.yml
@@ -6,11 +6,11 @@ on:
     branches:
       - main
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+
 permissions:
-  # deployments permission to deploy GitHub pages website
-  deployments: write
-  # contents permission to update benchmark contents in gh-pages branch
-  contents: write
+  contents: read # checkout
 
 env:
   CARGO_TERM_COLOR: always
@@ -20,6 +20,9 @@ jobs:
   benchmark:
     name: Performance regression check
     runs-on: ubuntu-latest
+    permissions:
+      deployments: write # deploy GitHub Pages website
+      contents: write # update benchmark results in gh-pages branch
 
     services:
       postgres:
@@ -37,16 +40,20 @@ jobs:
           --health-retries 5
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@3c5f7ea28cd621ae0bf5283f0e981fb97b8a7af9 # master
+        with:
+          toolchain: stable
 
       - name: Run benchmarks
         run: cargo bench -- --output-format bencher | tee output.txt
 
       - name: Store benchmark result
-        uses: benchmark-action/github-action-benchmark@v1
+        uses: benchmark-action/github-action-benchmark@a60cea5bc7b49e15c1f58f411161f99e0df48372 # v1.22.0
         with:
           name: Criterion Benchmark
           tool: 'cargo'
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b80da00..3455d3e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -6,29 +6,40 @@ on:
   merge_group:
     branches: [main]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read # checkout
+
 env:
   CARGO_TERM_COLOR: always
   DATABASE_URL: postgres://postgres:postgres@localhost:5436/test
 
 jobs:
   ci:
+    name: ci
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
 
       - name: Start Postgres
         run: docker compose up -d --wait
 
       - name: Install uv
-        uses: astral-sh/setup-uv@v4
+        uses: astral-sh/setup-uv@38f3f104447c67c051c4a08e39b64a148898af3a # v4.2.0
 
       - name: Validate schema matches migrations
         run: ./scripts/validate-schema
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@3c5f7ea28cd621ae0bf5283f0e981fb97b8a7af9 # master
         with:
+          toolchain: stable
           components: rustfmt, clippy
 
       - name: Check formatting
@@ -38,7 +49,7 @@ jobs:
         run: cargo clippy --all-targets --all-features -- -D warnings
 
       - name: Install nextest
-        uses: taiki-e/install-action@v2
+        uses: taiki-e/install-action@1329c298aa20c3257846c9b2e0e55967df3e3c37 # v2.75.25
         with:
           tool: cargo-nextest
 
diff --git a/.github/workflows/security.yml b/.github/workflows/security.yml
new file mode 100644
index 0000000..ba14316
--- /dev/null
+++ b/.github/workflows/security.yml
@@ -0,0 +1,65 @@
+name: security
+
+on:
+  pull_request:
+  merge_group:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  pinact:
+    name: pinact
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+
+      - uses: suzuki-shunsuke/pinact-action@cf51507d80d4d6522a07348e3d58790290eaf0b6 # v2.0.0
+        with:
+          skip_push: "true" # validate only; fail CI on unpinned actions
+
+  zizmor:
+    name: zizmor
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      security-events: write # upload SARIF findings to Code Scanning
+      actions: read # required by zizmor-action for private/internal repos
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+
+      - uses: zizmorcore/zizmor-action@b1d7e1fb5de872772f31590499237e7cce841e8e # v0.5.3
+        with:
+          persona: pedantic
+
+  security:
+    name: security
+    permissions: {}
+    if: always()
+    needs:
+      - pinact
+      - zizmor
+    runs-on: ubuntu-latest
+    steps:
+      - name: Print all job results
+        env:
+          NEEDS_JSON: ${{ toJson(needs) }}
+          GITHUB_EVENT_NAME: ${{ github.event_name }}
+        run: |
+          echo "'needs': ${NEEDS_JSON}"
+          echo "github.event_name: ${GITHUB_EVENT_NAME}"
+
+      # In the merge queue, any skipped job is a failure (everything must run).
+      # In PR CI, skips are allowed (e.g. fork PRs without OIDC).
+      - if: ${{ contains(needs.*.result, 'failure') || contains(needs.*.result, 'cancelled') || (github.event_name == 'merge_group' && contains(needs.*.result, 'skipped')) }}
+        run: exit 1
diff --git a/.github/zizmor.yml b/.github/zizmor.yml
new file mode 100644
index 0000000..5626e3a
--- /dev/null
+++ b/.github/zizmor.yml
@@ -0,0 +1,30 @@
+rules:
+  dependabot-cooldown:
+    config:
+      days: 3
+
+  # pinact owns SHA-pinning enforcement; suppress here to avoid duplicate failures.
+  unpinned-uses:
+    ignore:
+      - ci.yml
+      - benchmark.yml
+
+  # dtolnay/rust-toolchain is preferred over plain rustup for its caching and
+  # parallel component install behaviour — keeping it is an explicit choice.
+  superfluous-actions:
+    ignore:
+      - ci.yml
+      - benchmark.yml
+
+  # dtolnay/rust-toolchain publishes only via `master`; no tags exist to pin to,
+  # so a SHA pointing at master is the best available reference.
+  stale-action-refs:
+    ignore:
+      - ci.yml
+      - benchmark.yml
+
+  # The Postgres service container is for ephemeral test/bench use only; pinning
+  # to a SHA256 digest would add maintenance churn with no security benefit.
+  unpinned-images:
+    ignore:
+      - benchmark.yml