diff --git a/.github/actions/setup-swift/action.yml b/.github/actions/setup-swift/action.yml
new file mode 100644
index 0000000..8d1c534
--- /dev/null
+++ b/.github/actions/setup-swift/action.yml
@@ -0,0 +1,39 @@
+name: Setup Swift
+description: Install and cache a verified Swift release using Swiftly.
+
+inputs:
+  swift-version:
+    description: Exact Swift release version to install
+    required: true
+
+runs:
+  using: composite
+  steps:
+    - name: Locate tool cache
+      id: tool-cache
+      shell: bash
+      env:
+        SWIFT_VERSION: ${{ inputs.swift-version }}
+      run: |
+        if [[ ! "$SWIFT_VERSION" =~ ^[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
+          echo "::error::swift-version must be an exact release, e.g. 6.4.0."
+          exit 1
+        fi
+        ARCH=$(printf '%s' "$RUNNER_ARCH" | tr '[:upper:]' '[:lower:]')
+        CACHE_PATH="$RUNNER_TOOL_CACHE/swift/$SWIFT_VERSION/$ARCH"
+        echo "path=$CACHE_PATH" >> "$GITHUB_OUTPUT"
+
+    - name: Cache Swift toolchain
+      uses: actions/cache@v6
+      with:
+        path: |
+          ${{ steps.tool-cache.outputs.path }}
+          ${{ steps.tool-cache.outputs.path }}.complete
+        key: swift-${{ runner.os }}-${{ runner.arch }}-${{ env.ImageOS }}-${{ env.ImageVersion }}-${{ inputs.swift-version }}-${{ hashFiles('.github/actions/setup-swift/**') }}
+
+    - name: Install and select Swift
+      shell: bash
+      env:
+        SWIFT_VERSION: ${{ inputs.swift-version }}
+        SWIFT_CACHE_PATH: ${{ steps.tool-cache.outputs.path }}
+      run: bash "$GITHUB_ACTION_PATH/setup.sh"
diff --git a/.github/actions/setup-swift/setup.sh b/.github/actions/setup-swift/setup.sh
new file mode 100644
index 0000000..c900f11
--- /dev/null
+++ b/.github/actions/setup-swift/setup.sh
@@ -0,0 +1,83 @@
+#!/usr/bin/env bash
+set -euo pipefail
+: "${SWIFT_VERSION:?SWIFT_VERSION is required}"
+
+export SWIFTLY_HOME_DIR="$SWIFT_CACHE_PATH/home"
+export SWIFTLY_BIN_DIR="$SWIFT_CACHE_PATH/bin"
+export SWIFTLY_TOOLCHAINS_DIR="$SWIFT_CACHE_PATH/toolchains"
+
+# Keep Swiftly's version selection outside the checked-out repository.
+mkdir -p "$SWIFT_CACHE_PATH"
+cd "$SWIFT_CACHE_PATH"
+
+if [[ ! -f "$SWIFT_CACHE_PATH.complete" ]]; then
+  SWIFTLY_VERSION=1.1.4
+  DOWNLOAD_DIR=$(mktemp -d "$RUNNER_TEMP/setup-swift.XXXXXX")
+
+  case "$RUNNER_OS" in
+    Linux)
+      URL="https://download.swift.org/swiftly/linux"
+      URL="$URL/swiftly-$SWIFTLY_VERSION-$(uname -m).tar.gz"
+      curl --fail --silent --show-error --location "$URL" \
+        --output "$DOWNLOAD_DIR/swiftly.tar.gz"
+      curl --fail --silent --show-error --location "$URL.sig" \
+        --output "$DOWNLOAD_DIR/swiftly.tar.gz.sig"
+      curl --compressed --fail --silent --show-error --location \
+        https://swift.org/keys/all-keys.asc \
+        --output "$DOWNLOAD_DIR/swift-keys.asc"
+      # Swiftly's bootstrap signature must be checked before executing it.
+      gpg --batch --import "$DOWNLOAD_DIR/swift-keys.asc"
+      gpg --batch --verify "$DOWNLOAD_DIR/swiftly.tar.gz.sig" \
+        "$DOWNLOAD_DIR/swiftly.tar.gz"
+      tar -xzf "$DOWNLOAD_DIR/swiftly.tar.gz" -C "$DOWNLOAD_DIR"
+      SWIFTLY="$DOWNLOAD_DIR/swiftly"
+      ;;
+    macOS)
+      URL="https://download.swift.org/swiftly/darwin"
+      curl --fail --silent --show-error --location \
+        "$URL/swiftly-$SWIFTLY_VERSION.pkg" \
+        --output "$DOWNLOAD_DIR/swiftly.pkg"
+      pkgutil --check-signature "$DOWNLOAD_DIR/swiftly.pkg"
+      pkgutil --expand "$DOWNLOAD_DIR/swiftly.pkg" "$DOWNLOAD_DIR/package"
+      mkdir -p "$DOWNLOAD_DIR/extracted"
+      tar -xf "$DOWNLOAD_DIR/package"/swiftly-*/Payload \
+        -C "$DOWNLOAD_DIR/extracted"
+      SWIFTLY="$DOWNLOAD_DIR/extracted/bin/swiftly"
+      ;;
+    *)
+      echo "::error::Unsupported runner OS: $RUNNER_OS"
+      exit 1
+      ;;
+  esac
+
+  "$SWIFTLY" init --skip-install --quiet-shell-followup \
+    --assume-yes --no-modify-profile
+  "$SWIFTLY_BIN_DIR/swiftly" install "$SWIFT_VERSION" --use --assume-yes \
+    --post-install-file "$SWIFT_CACHE_PATH/post-install.sh"
+fi
+
+# A restored toolchain still needs its system dependencies on a fresh runner.
+if [[ -f "$SWIFT_CACHE_PATH/post-install.sh" ]]; then
+  if [[ "$RUNNER_OS" == Linux ]]; then
+    sudo apt-get update
+  fi
+  sudo bash "$SWIFT_CACHE_PATH/post-install.sh"
+fi
+
+TOOLCHAIN=$("$SWIFTLY_BIN_DIR/swiftly" use --print-location)
+SWIFT_BIN="$TOOLCHAIN/usr/bin"
+VERSION_OUTPUT=$("$SWIFT_BIN/swift" --version)
+printf '%s\n' "$VERSION_OUTPUT"
+ACTUAL_VERSION=$(printf '%s\n' "$VERSION_OUTPUT" \
+  | sed -nE 's/.*Swift version ([0-9]+\.[0-9]+(\.[0-9]+)?).*/\1/p')
+if [[ "$ACTUAL_VERSION" =~ ^[0-9]+\.[0-9]+$ ]]; then
+  ACTUAL_VERSION="$ACTUAL_VERSION.0"
+fi
+if [[ "$ACTUAL_VERSION" != "$SWIFT_VERSION" ]]; then
+  echo "::error::Expected Swift $SWIFT_VERSION, got $ACTUAL_VERSION"
+  exit 1
+fi
+
+# Match the runner tool-cache convention: publish only complete installations.
+touch "$SWIFT_CACHE_PATH.complete"
+printf '%s\n' "$SWIFT_BIN" >> "$GITHUB_PATH"
diff --git a/.github/workflows/analyze.yml b/.github/workflows/analyze.yml
index fbebb64..1ac2892 100644
--- a/.github/workflows/analyze.yml
+++ b/.github/workflows/analyze.yml
@@ -23,9 +23,9 @@ jobs:
         uses: actions/checkout@v7
 
       - name: Setup Swift
-        uses: swift-actions/setup-swift@v3
+        uses: ./.github/actions/setup-swift
         with:
-          swift-version: "6.3.3"
+          swift-version: "6.4.0"
 
       - name: Install analysis tools
         run: brew bundle --file Brewfile-ci
diff --git a/.github/workflows/build-binaries.yml b/.github/workflows/build-binaries.yml
index 975d001..976e822 100644
--- a/.github/workflows/build-binaries.yml
+++ b/.github/workflows/build-binaries.yml
@@ -46,9 +46,9 @@ jobs:
         uses: actions/checkout@v7
 
       - name: Setup Swift
-        uses: swift-actions/setup-swift@v3
+        uses: ./.github/actions/setup-swift
         with:
-          swift-version: "6.3.3"
+          swift-version: "6.4.0"
 
       - name: Generate build metadata
         uses: ./.github/actions/generate-build-metadata
@@ -123,15 +123,15 @@ jobs:
         uses: actions/checkout@v7
 
       - name: Setup Swift
-        uses: swift-actions/setup-swift@v3
+        uses: ./.github/actions/setup-swift
         with:
-          swift-version: "6.3.3"
+          swift-version: "6.4.0"
 
       - name: Install Static Linux SDK
         run: |
           swift sdk install \
-            "https://download.swift.org/swift-6.3.3-release/static-sdk/swift-6.3.3-RELEASE/swift-6.3.3-RELEASE_static-linux-0.1.0.artifactbundle.tar.gz" \
-            --checksum "87c3eaf908e67c0e13a84367119e12273cec1d2cd3d81f7d74bb36722d6b607b"
+            "https://download.swift.org/swift-6.4.0-release/static-sdk/swift-6.4.0-RELEASE/swift-6.4.0-RELEASE_static-linux-0.1.0.artifactbundle.tar.gz" \
+            --checksum "47d2fd89eebfdf9eb4d536b6710414297f755c17926cdebc4742c08982b40a9e"
 
       - name: Generate build metadata
         uses: ./.github/actions/generate-build-metadata
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 199ed9a..5f0cb2f 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -23,9 +23,9 @@ jobs:
         uses: actions/checkout@v7
 
       - name: Setup Swift
-        uses: swift-actions/setup-swift@v3
+        uses: ./.github/actions/setup-swift
         with:
-          swift-version: "6.3.3"
+          swift-version: "6.4.0"
 
       - name: Make Build
         run: make build
diff --git a/.github/workflows/format.yml b/.github/workflows/format.yml
index 5c1c430..ae49f3f 100644
--- a/.github/workflows/format.yml
+++ b/.github/workflows/format.yml
@@ -23,9 +23,9 @@ jobs:
         uses: actions/checkout@v7
 
       - name: Setup Swift
-        uses: swift-actions/setup-swift@v3
+        uses: ./.github/actions/setup-swift
         with:
-          swift-version: "6.3.3"
+          swift-version: "6.4.0"
 
       - name: Install formatting tools
         run: brew bundle --file Brewfile-ci
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 9dbc2e2..e475fe0 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -23,9 +23,9 @@ jobs:
         uses: actions/checkout@v7
 
       - name: Setup Swift
-        uses: swift-actions/setup-swift@v3
+        uses: ./.github/actions/setup-swift
         with:
-          swift-version: "6.3.3"
+          swift-version: "6.4.0"
 
       - name: Make Test
         run: make test
@@ -39,9 +39,9 @@ jobs:
         uses: actions/checkout@v7
 
       - name: Setup Swift
-        uses: swift-actions/setup-swift@v3
+        uses: ./.github/actions/setup-swift
         with:
-          swift-version: "6.3.3"
+          swift-version: "6.4.0"
 
       - name: Make Test
         run: make test
diff --git a/.yamllint.yml b/.yamllint.yml
new file mode 100644
index 0000000..bbcd868
--- /dev/null
+++ b/.yamllint.yml
@@ -0,0 +1,5 @@
+extends: default
+
+rules:
+  line-length:
+    max: 200