ci: adopt Worker Previews for playground

[ascorbic]

What does this PR do?

Switches playground PR deployments from the prerelease Worker Preview workaround to the current Worker Previews flow.

• Uses Wrangler 4.123.0 for the playground and refreshes its generated Worker types.
• Gives Preview deployments a dedicated SESSION KV namespace while keeping Durable Object state automatically isolated per Preview.
• Removes the legacy preview_urls setting and the GitHub Action that reconstructed Preview URLs from Cloudflare bot comments.
• Relies on Workers Builds to post the stable Preview URL and immutable Deployment URL directly on the PR.

Created Cloudflare resource: emdash-playground-preview-session (efd741f1e4d1443e841a187b3a4cb023).

Before merge, update the playground Worker in Dash:

1. Under Settings → Build, set NODE_OPTIONS=--max-old-space-size=6144 as a build variable.
2. Ensure Preview Builds is enabled with npx wrangler preview as the Preview command.

Related issue: none.

Type of change

• Bug fix
• Feature (requires maintainer-approved Discussion)
• Refactor (no behavior change)
• Translation
• Documentation
• Performance improvement
• Tests
• Chore (dependencies, CI, tooling)

Checklist

• I have read CONTRIBUTING.md
• pnpm typecheck passes
• pnpm lint passes
• pnpm test passes (or targeted tests for my change)
• pnpm format has been run
• I have added/updated tests for my changes (if applicable)
• User-visible strings in the admin UI are wrapped for translation (if applicable). Do not include messages.po changes except in translation PRs — a workflow extracts catalogs on merge to main.
• I have added a changeset (if this PR changes a published package)
• New features link to an approved Discussion: https://github.com/emdash-cms/emdash/discussions/...

The unchecked items are not applicable: this changes CI/demo configuration without application behavior, user-visible strings, or a published package.

AI-generated code disclosure

• This PR includes AI-generated code — model/tool: GPT-5 Codex

Screenshots / test output

No visual change.

Validated with:

• pnpm install --frozen-lockfile --lockfile-only
• pnpm build
• pnpm typecheck
• pnpm typecheck:demos
• pnpm lint
• pnpm format
• pnpm --filter @emdash-cms/playground build
• wrangler types --check
• wrangler deploy --dry-run

---

Try this PR

Open a fresh playground →

A full working EmDash site, deployed from this branch. Each visit gets its own session-scoped sandbox: no login needed and no shared state. Try the admin, edit content, hit the public site.

_{Tracks codex/worker-previews-cutover. Updated automatically when the playground redeploys.}

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[github-actions]

Scope check

This PR changes 1,338 lines across 6 files. Large PRs are harder to review and more likely to be closed without review.

If this scope is intentional, no action needed. A maintainer will review it. If not, please consider splitting this into smaller PRs.

See CONTRIBUTING.md for contribution guidelines.

[cloudflare-workers-and-pages]

Deploying with    Cloudflare Workers

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Status	Name	Latest Commit	Updated (UTC)
✅ Deployment successful! View logs	emdash-demo-cache	87010bb	Aug 17 2026, 04:29 PM

[cloudflare-workers-and-pages]

Deploying with    Cloudflare Workers

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Status	Name	Latest Commit	Updated (UTC)
✅ Deployment successful! View logs	emdash-playground	87010bb	Aug 17 2026, 04:28 PM

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commit: 87010bb

[changeset-bot]

⚠️ No Changeset found

Latest commit: 87010bb

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[cloudflare-workers-and-pages]

Deploying with    Cloudflare Workers

The latest updates on your project. Learn more about integrating Git with Workers.

Status	Name	Latest Commit	Updated (UTC)
✅ Deployment successful! View logs	emdash-demo-do	87010bb	Aug 17 2026, 04:29 PM