docs: move cookie-domain guidance to troubleshooting faq

[RiskeyL]

Summary

• Moves the cross-subdomain cookie-domain guidance from the Docker Compose quick-start callout to a new "Reverse Proxy Setup" entry in the FAQ. The original placement targets readers at the wrong moment: the issue surfaces at login-failure time after a reverse-proxy deployment, not at the .env-edit step during install. The FAQ entry is symptom-anchored ("Login Session Drops with Split Frontend and Backend Subdomains") so operators searching for the bug find it.
• Mirrored across en, zh, and ja.
• Cleans up pre-existing formatting issues in the same six files: heading title case, trailing whitespace, code-block spacing, missing bash language tags, and CJK-Latin spacing throughout the Japanese page.

COOKIE_DOMAIN and NEXT_PUBLIC_COOKIE_DOMAIN remain fully documented in the env vars reference, which the new FAQ entry links to.

[mintlify]

Preview deployment for your docs. Learn more about Mintlify Previews.

Project	Status	Preview	Updated (UTC)
dify-core-product	🟢 Ready	View Preview	Apr 30, 2026, 3:13 AM

💡 Tip: Enable Workflows to automatically generate PRs for you.

[Copilot]

Pull request overview

Moves cross-subdomain cookie-domain guidance to a symptom-driven FAQ entry so operators can find it when diagnosing reverse-proxy login/session issues, and aligns formatting across EN/JA/ZH quick-start docs.

Changes:

• Adds a new “Reverse Proxy Setup” FAQ entry covering session drops when frontend/backend are on different subdomains, with COOKIE_DOMAIN + NEXT_PUBLIC_COOKIE_DOMAIN guidance.
• Removes the same guidance from the Docker Compose quick-start callout to avoid surfacing it too early in the install flow.
• Fixes minor formatting issues (heading capitalization, whitespace, code block language tags, and spacing) across the touched docs.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
en/self-host/quick-start/faqs.mdx	Adds reverse-proxy FAQ entry; normalizes heading title case.
en/self-host/quick-start/docker-compose.mdx	Removes cookie guidance callout; adds bash language tag to restart snippet.
zh/self-host/quick-start/faqs.mdx	Adds reverse-proxy FAQ entry in Chinese; removes stray whitespace line.
zh/self-host/quick-start/docker-compose.mdx	Removes cookie guidance callout; fixes spacing around links; adds bash language tag.
ja/self-host/quick-start/faqs.mdx	Adds reverse-proxy FAQ entry in Japanese; fixes CJK-Latin spacing.
ja/self-host/quick-start/docker-compose.mdx	Removes cookie guidance callout; applies consistent spacing/formatting and adds bash language tag.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.