diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0859eca33..02a5a640e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -20,6 +20,9 @@ jobs:
       - name: Scan for security vulnerabilities in Ruby dependencies
         run: bin/brakeman --no-pager
 
+      - name: Validate preview deploy workflow hardening
+        run: ruby bin/preview_deploy_security_check.rb
+
   scan_js:
     runs-on: ubuntu-latest
     timeout-minutes: 10
diff --git a/.github/workflows/preview-deploy.yml b/.github/workflows/preview-deploy.yml
index 06b9c61e0..654c170e0 100644
--- a/.github/workflows/preview-deploy.yml
+++ b/.github/workflows/preview-deploy.yml
@@ -16,18 +16,26 @@ jobs:
     name: Deploy to Cloudflare Containers
     runs-on: ubuntu-latest
     timeout-minutes: 15
+    concurrency:
+      group: preview-deploy-${{ github.event.pull_request.number }}
+      cancel-in-progress: true
+    environment:
+      name: preview
     permissions:
       actions: read
       contents: read
       pull-requests: write
       deployments: write
+    env:
+      PR_NUMBER: ${{ github.event.pull_request.number }}
+      HEAD_SHA: ${{ github.event.pull_request.head.sha }}
 
     steps:
       - name: Wait for PR CI to pass
-        uses: actions/github-script@v7
+        uses: actions/github-script@f28e40c7f34bde8b3046d885e986cb6290c5673b # v7
         with:
           script: |
-            const headSha = context.payload.pull_request.head.sha;
+            const headSha = process.env.HEAD_SHA;
             const timeoutMs = 10 * 60 * 1000;
             const pollMs = 15 * 1000;
             const startedAt = Date.now();
@@ -65,35 +73,62 @@ jobs:
 
             core.setFailed(`Timed out waiting for Pull Request workflow for ${headSha}. Last state: ${lastState}`);
 
-      - name: Checkout code
-        uses: actions/checkout@v5
+      - name: Checkout PR code
+        uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
+        with:
+          path: pr
+          persist-credentials: false
+
+      - name: Checkout trusted preview tooling
+        uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
+        with:
+          ref: ${{ github.event.pull_request.base.sha }}
+          path: trusted
+          persist-credentials: false
+          sparse-checkout: |
+            workers/preview
 
       - name: Setup Node.js
-        uses: actions/setup-node@v6
+        uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6
         with:
           node-version: "24"
 
-      - name: Install Wrangler dependencies
-        working-directory: workers/preview
-        run: npm install
-
-      - name: Configure preview files for this PR
-        working-directory: workers/preview
+      - name: Prepare trusted preview deploy workspace
         run: |
-          sed -i "s/\${PR_NUMBER}/${{ github.event.pull_request.number }}/g" wrangler.toml
-          sed -i "s/\${PR_NUMBER}/${{ github.event.pull_request.number }}/g" src/index.ts
-          cat wrangler.toml
+          set -euo pipefail
+
+          preview_dir="$RUNNER_TEMP/sure-preview-worker"
+          rm -rf "$preview_dir"
+          mkdir -p "$preview_dir"
+
+          cp trusted/workers/preview/package.json "$preview_dir/package.json"
+          cp trusted/workers/preview/package-lock.json "$preview_dir/package-lock.json"
+          cp trusted/workers/preview/tsconfig.json "$preview_dir/tsconfig.json"
+          cp trusted/workers/preview/wrangler.toml "$preview_dir/wrangler.toml"
+          cp -R pr/workers/preview/src "$preview_dir/src"
+
+          sed -i "s/\${PR_NUMBER}/${PR_NUMBER}/g" "$preview_dir/wrangler.toml"
+          sed -i "s/\${PR_NUMBER}/${PR_NUMBER}/g" "$preview_dir/src/index.ts"
+          sed -i \
+            "s#image = \"../../Dockerfile.preview\"#image = \"${GITHUB_WORKSPACE}/pr/Dockerfile.preview\"#" \
+            "$preview_dir/wrangler.toml"
+
+          cat "$preview_dir/wrangler.toml"
+          cd "$preview_dir"
+          npm ci --ignore-scripts --no-audit --no-fund
 
       - name: Create GitHub Deployment
         id: deployment
-        uses: actions/github-script@v7
+        uses: actions/github-script@f28e40c7f34bde8b3046d885e986cb6290c5673b # v7
         with:
           script: |
+            const prNumber = process.env.PR_NUMBER;
+            const headSha = process.env.HEAD_SHA;
             const deployment = await github.rest.repos.createDeployment({
               owner: context.repo.owner,
               repo: context.repo.repo,
-              ref: context.payload.pull_request.head.sha,
-              environment: `preview-pr-${{ github.event.pull_request.number }}`,
+              ref: headSha,
+              environment: `preview-pr-${prNumber}`,
               auto_merge: false,
               required_contexts: [],
               description: 'PR Preview Deployment'
@@ -103,15 +138,18 @@ jobs:
 
       - name: Deploy to Cloudflare Containers
         id: deploy
-        working-directory: workers/preview
         env:
           CLOUDFLARE_API_TOKEN: ${{ secrets.CLOUDFLARE_API_TOKEN }}
           CLOUDFLARE_ACCOUNT_ID: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}
+          CLOUDFLARE_WORKERS_SUBDOMAIN: ${{ secrets.CLOUDFLARE_WORKERS_SUBDOMAIN }}
         run: |
-          npx wrangler deploy --var "PR_NUMBER:${{ github.event.pull_request.number }}"
+          set -euo pipefail
+
+          cd "$RUNNER_TEMP/sure-preview-worker"
+          ./node_modules/.bin/wrangler deploy --config wrangler.toml --var "PR_NUMBER:${PR_NUMBER}"
 
           # Get the deployment URL
-          PREVIEW_URL="https://sure-preview-${{ github.event.pull_request.number }}.${{ secrets.CLOUDFLARE_WORKERS_SUBDOMAIN }}.workers.dev"
+          PREVIEW_URL="https://sure-preview-${PR_NUMBER}.${CLOUDFLARE_WORKERS_SUBDOMAIN}.workers.dev"
           echo "preview_url=${PREVIEW_URL}" >> "$GITHUB_OUTPUT"
 
       - name: Warm preview container
@@ -123,25 +161,33 @@ jobs:
 
       - name: Update Deployment Status
         if: always() && steps.deployment.outputs.result
-        uses: actions/github-script@v7
+        uses: actions/github-script@f28e40c7f34bde8b3046d885e986cb6290c5673b # v7
+        env:
+          DEPLOYMENT_ID: ${{ steps.deployment.outputs.result }}
+          PREVIEW_URL: ${{ steps.deploy.outputs.preview_url }}
         with:
           script: |
             const state = '${{ job.status }}' === 'success' ? 'success' : 'failure';
+            const previewUrl = process.env.PREVIEW_URL || undefined;
             await github.rest.repos.createDeploymentStatus({
               owner: context.repo.owner,
               repo: context.repo.repo,
-              deployment_id: ${{ steps.deployment.outputs.result }},
+              deployment_id: Number(process.env.DEPLOYMENT_ID),
               state: state,
-              environment_url: state === 'success' ? '${{ steps.deploy.outputs.preview_url }}' : undefined,
+              environment_url: state === 'success' ? previewUrl : undefined,
               description: state === 'success' ? 'Preview deployed successfully' : 'Preview deployment failed'
             });
 
       - name: Comment on PR
         if: success()
-        uses: actions/github-script@v7
+        uses: actions/github-script@f28e40c7f34bde8b3046d885e986cb6290c5673b # v7
+        env:
+          PREVIEW_URL: ${{ steps.deploy.outputs.preview_url }}
         with:
           script: |
-            const previewUrl = '${{ steps.deploy.outputs.preview_url }}';
+            const previewUrl = process.env.PREVIEW_URL;
+            const issueNumber = Number(process.env.PR_NUMBER);
+            const headSha = process.env.HEAD_SHA;
             const commentBody = `## 🚀 Preview Deployment Ready
 
             Your preview environment has been deployed to Cloudflare Containers with the PR's Docker image.
@@ -152,13 +198,13 @@ jobs:
             > 💤 The container will sleep after 30 minutes of inactivity and wake on the next request.
 
             ---
-            <sub>Deployed from commit ${{ github.event.pull_request.head.sha }}</sub>`;
+            <sub>Deployed from commit ${headSha}</sub>`;
 
             // Find existing comment
             const { data: comments } = await github.rest.issues.listComments({
               owner: context.repo.owner,
               repo: context.repo.repo,
-              issue_number: ${{ github.event.pull_request.number }}
+              issue_number: issueNumber
             });
 
             const botComment = comments.find(comment =>
@@ -177,15 +223,14 @@ jobs:
               await github.rest.issues.createComment({
                 owner: context.repo.owner,
                 repo: context.repo.repo,
-                issue_number: ${{ github.event.pull_request.number }},
+                issue_number: issueNumber,
                 body: commentBody
               });
             }
       - name: Store cleanup metadata
         if: success()
-        uses: actions/upload-artifact@v6
+        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6
         with:
-          name: preview-cleanup-pr-${{ github.event.pull_request.number }}
-          path: |
-            workers/preview/wrangler.toml
+          name: preview-cleanup-pr-${{ env.PR_NUMBER }}
+          path: ${{ runner.temp }}/sure-preview-worker/wrangler.toml
           retention-days: 2
diff --git a/bin/preview_deploy_security_check.rb b/bin/preview_deploy_security_check.rb
new file mode 100644
index 000000000..fa4eb493d
--- /dev/null
+++ b/bin/preview_deploy_security_check.rb
@@ -0,0 +1,136 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+%w[json pathname yaml].each { |library| require library }
+
+ROOT = File.expand_path("..", __dir__)
+WORKFLOW_PATH = File.join(ROOT, ".github/workflows/preview-deploy.yml")
+LOCKFILE_PATH = File.join(ROOT, "workers/preview/package-lock.json")
+PINNED_ACTION = /\A[^@\s]+@[a-f0-9]{40}\z/
+INLINE_SECRET_EXPRESSION = /\$\{\{\s*secrets\s*(?:\.|\[)/i
+INLINE_PR_EXPRESSION = /
+  \$\{\{\s*
+  github\s*
+  (?:\.\s*event|\[\s*['"]event['"]\s*\])\s*
+  (?:\.\s*pull_request|\[\s*['"]pull_request['"]\s*\])
+/ix
+PR_CONTROLLED_WORKDIR = %r{\A(?:pr|workers/preview)(?:/|\z)}
+GITHUB_WORKSPACE_PREFIX = %r{
+  \A
+  (?:
+    \$GITHUB_WORKSPACE |
+    \$\{\{\s*github\s*(?:\.\s*workspace|\[\s*['"]workspace['"]\s*\])\s*\}\}
+  )
+  (?:/|\z)
+}ix
+EXPECTED_PERMISSIONS = { "actions" => "read", "contents" => "read", "pull-requests" => "write", "deployments" => "write" }.freeze
+EXPECTED_SECRET_ENV = %w[CLOUDFLARE_ACCOUNT_ID CLOUDFLARE_API_TOKEN CLOUDFLARE_WORKERS_SUBDOMAIN].freeze
+REQUIRED_PREPARE_LINES = [
+  'cp trusted/workers/preview/package.json "$preview_dir/package.json"',
+  'cp trusted/workers/preview/package-lock.json "$preview_dir/package-lock.json"',
+  'cp trusted/workers/preview/tsconfig.json "$preview_dir/tsconfig.json"',
+  'cp trusted/workers/preview/wrangler.toml "$preview_dir/wrangler.toml"',
+  'cp -R pr/workers/preview/src "$preview_dir/src"',
+  'image = \"${GITHUB_WORKSPACE}/pr/Dockerfile.preview\"',
+  "npm ci --ignore-scripts --no-audit --no-fund"
+].freeze
+
+def fail_check(message)
+  warn "preview-deploy security check failed: #{message}"
+  exit 1
+end
+
+def assert(value, message)
+  fail_check(message) unless value
+end
+
+def step!(steps, name)
+  steps.find { |step| step["name"] == name } || fail_check("missing #{name.inspect} step")
+end
+
+def run(step)
+  step.fetch("run", "")
+end
+
+def assert_run_includes(step, *needles)
+  script = run(step)
+  needles.each { |needle| assert(script.include?(needle), "#{step["name"]} must include #{needle.inspect}") }
+  script
+end
+
+def normalized_working_directory(value)
+  path = value.to_s.strip.sub(GITHUB_WORKSPACE_PREFIX, "")
+  normalized = Pathname.new(path).cleanpath.to_s
+
+  normalized == "." ? "" : normalized
+end
+
+def environment_name(job)
+  environment = job["environment"]
+  environment.is_a?(Hash) ? environment["name"] : environment
+end
+
+workflow = YAML.safe_load_file(WORKFLOW_PATH, aliases: true)
+lockfile = JSON.parse(File.read(LOCKFILE_PATH))
+job = workflow.fetch("jobs").fetch("deploy-preview")
+steps = job.fetch("steps")
+step_names = steps.map { |step| step["name"] }
+pr_checkout = step!(steps, "Checkout PR code")
+trusted_checkout = step!(steps, "Checkout trusted preview tooling")
+prepare = step!(steps, "Prepare trusted preview deploy workspace")
+deploy = step!(steps, "Deploy to Cloudflare Containers")
+wrangler = lockfile.fetch("packages").fetch("node_modules/wrangler")
+
+[
+  [ "job permissions", job.fetch("permissions"), EXPECTED_PERMISSIONS ],
+  [ "job environment", environment_name(job), "preview" ],
+  [ "concurrency group", job.dig("concurrency", "group"), "preview-deploy-${{ github.event.pull_request.number }}" ],
+  [ "concurrency cancellation", job.dig("concurrency", "cancel-in-progress"), true ],
+  [ "PR_NUMBER env", job.dig("env", "PR_NUMBER"), "${{ github.event.pull_request.number }}" ],
+  [ "HEAD_SHA env", job.dig("env", "HEAD_SHA"), "${{ github.event.pull_request.head.sha }}" ],
+  [ "PR checkout path", pr_checkout.dig("with", "path"), "pr" ],
+  [ "PR checkout credentials", pr_checkout.dig("with", "persist-credentials"), false ],
+  [ "trusted checkout ref", trusted_checkout.dig("with", "ref"), "${{ github.event.pull_request.base.sha }}" ],
+  [ "trusted checkout path", trusted_checkout.dig("with", "path"), "trusted" ],
+  [ "trusted checkout credentials", trusted_checkout.dig("with", "persist-credentials"), false ],
+  [ "deploy secret env", deploy.fetch("env").keys.sort, EXPECTED_SECRET_ENV ],
+  [ "Wrangler binary", wrangler.dig("bin", "wrangler"), "bin/wrangler.js" ]
+].each { |label, actual, expected| assert(actual == expected, "#{label}: expected #{actual.inspect} to equal #{expected.inspect}") }
+
+assert(lockfile.dig("packages", "", "devDependencies", "wrangler"), "Wrangler must stay a root dev dependency")
+assert(lockfile.fetch("lockfileVersion") >= 3, "preview tooling lockfile must preserve npm ci integrity metadata")
+assert(wrangler.fetch("resolved").start_with?("https://registry.npmjs.org/wrangler/-/wrangler-"), "Wrangler must resolve from npm registry")
+assert(wrangler.fetch("integrity").start_with?("sha512-"), "Wrangler lockfile entry must keep npm integrity metadata")
+assert(trusted_checkout.dig("with", "sparse-checkout").to_s.include?("workers/preview"), "trusted checkout must include preview tooling")
+assert(step_names.compact.uniq == step_names.compact, "workflow step names must stay unique for security checks")
+assert([ pr_checkout, trusted_checkout, prepare, deploy ].map { |step| steps.index(step) }.each_cons(2).all? { |left, right| left < right }, "checkout, preparation, and deploy steps must stay ordered")
+assert(job.fetch("env").keys.none? { |name| name.start_with?("CLOUDFLARE_") }, "Cloudflare secrets must not be job-wide")
+assert(EXPECTED_SECRET_ENV.all? { |name| deploy.fetch("env").fetch(name).start_with?("${{ secrets.") }, "deploy secret env must be sourced from GitHub secrets")
+
+steps.each do |step|
+  uses = step["uses"]
+  assert(uses.start_with?("./") || uses.match?(PINNED_ACTION), "#{step["name"] || uses} must pin external actions") if uses
+end
+
+inline_scripts = steps.flat_map { |step| [ run(step), step.dig("with", "script") ] }.compact.join("\n")
+assert(!inline_scripts.match?(INLINE_SECRET_EXPRESSION), "secrets must enter scripts through env")
+assert(!inline_scripts.match?(INLINE_PR_EXPRESSION), "PR fields must enter scripts through env")
+assert(steps.none? { |step| normalized_working_directory(step["working-directory"]).match?(PR_CONTROLLED_WORKDIR) }, "steps must not run from PR-controlled dirs")
+assert(steps.none? { |step| run(step).include?("npx wrangler") }, "workflow must not use npx wrangler")
+
+prepare_run = assert_run_includes(prepare, *REQUIRED_PREPARE_LINES)
+assert(!prepare_run.include?("npm install"), "prepare step must not use npm install")
+assert(!prepare_run.include?("CLOUDFLARE_API_TOKEN"), "prepare step must not receive Cloudflare secrets")
+assert([ prepare, deploy ].all? { |step| run(step).include?("set -euo pipefail") }, "trusted setup and deploy scripts must fail closed")
+assert(prepare_run.include?('preview_dir="$RUNNER_TEMP/sure-preview-worker"'), "trusted workspace must be created under RUNNER_TEMP")
+assert(steps.select { |step| run(step).match?(/npm (ci|install)/) }.map { |step| step["name"] } == [ prepare["name"] ], "only prepare may install deploy tooling")
+
+secret_steps = steps.select { |step| step.fetch("env", {}).then { |env| env.key?("CLOUDFLARE_API_TOKEN") || env.key?("CLOUDFLARE_ACCOUNT_ID") } }
+assert(secret_steps.map { |step| step["name"] } == [ deploy["name"] ], "only deploy may receive Cloudflare secrets")
+secret_steps.each do |step|
+  assert(step["working-directory"].nil?, "#{step["name"]} must not run from a PR-controlled working directory")
+  assert(!run(step).match?(/npx wrangler|npm (ci|install)/), "#{step["name"]} must not execute PR-controlled tooling with secrets")
+end
+
+assert_run_includes(deploy, 'cd "$RUNNER_TEMP/sure-preview-worker"', "./node_modules/.bin/wrangler deploy --config wrangler.toml", '--var "PR_NUMBER:${PR_NUMBER}"')
+puts "preview-deploy security check passed"