diff --git a/.github/workflows/demo.yml b/.github/workflows/demo.yml
index 82ab4f88..1e16b344 100644
--- a/.github/workflows/demo.yml
+++ b/.github/workflows/demo.yml
@@ -136,6 +136,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 10
     permissions: {}
+    environment: demo
     outputs:
       url: ${{ steps.version.outputs.url }}
       id: ${{ steps.version.outputs.id }}
@@ -214,7 +215,8 @@ jobs:
           mkdir -p placeholder/site
           printf '<!doctype html><meta charset="utf-8"><title>Stackyard demo</title><p>The demo is being prepared.</p>\n' > placeholder/site/index.html
           printf '/ /index.html 200\n' > placeholder/site/_redirects
-          cp upload/wrangler.jsonc placeholder/
+          # Without the routes, so a placeholder never takes the demo address.
+          node -e 'const c = JSON.parse(require("fs").readFileSync(process.argv[1], "utf8")); delete c.routes; require("fs").writeFileSync(process.argv[2], JSON.stringify(c, null, 2));' upload/wrangler.jsonc placeholder/wrangler.jsonc
 
       - name: Create the Worker
         if: steps.creds.outputs.set == 'true' && steps.worker.outputs.exists == 'false'
@@ -303,11 +305,31 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 10
     permissions: {}
+    environment: demo
     steps:
-      - name: Deploy the version
+      - name: Checkout the Wrangler config
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+          path: repo
+          sparse-checkout: scripts/demo/wrangler.jsonc
+          sparse-checkout-cone-mode: false
+
+      - name: Prepare the config
+        run: |
+          set -euo pipefail
+          mkdir -p promote/site
+          cp repo/scripts/demo/wrangler.jsonc promote/
+          rm -rf repo
+
+      # Version uploads leave routes alone; triggers deploy applies the demo address.
+      - name: Deploy the version and its address
         uses: cloudflare/wrangler-action@953926a2e2182532811c01a25e53647d93bf07c0 # v4.1.3
         with:
           apiToken: ${{ secrets.CLOUDFLARE_API_TOKEN }}
           accountId: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}
           wranglerVersion: ${{ env.WRANGLER_VERSION }}
-          command: versions deploy ${{ needs.upload.outputs.id }}@100 --name stackyard-demo --yes --message "Stackyard ${{ inputs.version }}"
+          workingDirectory: promote
+          command: |
+            versions deploy ${{ needs.upload.outputs.id }}@100 --yes --message "Stackyard ${{ inputs.version }}"
+            triggers deploy
diff --git a/scripts/demo/wrangler.jsonc b/scripts/demo/wrangler.jsonc
index 688219c6..2a8491c6 100644
--- a/scripts/demo/wrangler.jsonc
+++ b/scripts/demo/wrangler.jsonc
@@ -4,6 +4,7 @@
   "compatibility_date": "2026-10-01",
   "workers_dev": true,
   "preview_urls": true,
+  "routes": [{ "pattern": "demo.sandobserver.com", "custom_domain": true }],
   "assets": {
     "directory": "./site",
     "html_handling": "none",
diff --git a/test/repo/demo-workflow.test.js b/test/repo/demo-workflow.test.js
new file mode 100644
index 00000000..b1306c4e
--- /dev/null
+++ b/test/repo/demo-workflow.test.js
@@ -0,0 +1,33 @@
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const yaml = require('js-yaml');
+
+const root = path.join(__dirname, '..', '..');
+const wf = yaml.load(fs.readFileSync(path.join(root, '.github', 'workflows', 'demo.yml'), 'utf8'));
+const config = JSON.parse(fs.readFileSync(path.join(root, 'scripts', 'demo', 'wrangler.jsonc'), 'utf8'));
+const usesSecret = job => JSON.stringify(job).includes('secrets.CLOUDFLARE');
+
+test('only the demo environment hands out the Cloudflare token', () => {
+  for (const [name, job] of Object.entries(wf.jobs)) {
+    if (usesSecret(job))
+      assert.equal(job.environment, 'demo', `${name} reads a Cloudflare secret outside the environment`);
+  }
+  assert.ok(!usesSecret(wf.jobs.build), 'the build job runs dev dependencies');
+  assert.ok(!usesSecret(wf.jobs.verify), 'the verify job runs dev dependencies');
+});
+
+test('the demo address is in the config and applied when a version goes live', () => {
+  assert.deepEqual(config.routes, [{ pattern: 'demo.sandobserver.com', custom_domain: true }]);
+  const deploy = wf.jobs.promote.steps.find(s => String(s.with?.command || '').includes('versions deploy'));
+  assert.ok(deploy, 'the promote job no longer deploys a version');
+  assert.match(deploy.with.command, /^\s*triggers deploy\s*$/m, 'a version upload alone leaves the address unset');
+});
+
+test('the first-run placeholder never takes the demo address', () => {
+  const prep = wf.jobs.upload.steps.find(s => s.name === 'Prepare the placeholder');
+  assert.ok(prep, 'the placeholder step is gone');
+  assert.match(prep.run, /delete c\.routes/);
+  assert.doesNotMatch(prep.run, /cp upload\/wrangler\.jsonc placeholder/);
+});