Setting a wildcard access URL is practically a requirement for any Coder deployment that supports web IDEs (e.g. code-server) and needs preview URLs for an app.

Frameworks like Vite, React, Express, etc. do not support path-based apps (coder.example.com/workspace-name/proxy/4200/) by default and some modules (e.g. KasmVNC) do not support path-based apps.

Additionally, when configured, there is a DNS character limit that often fail: #15178

See related ProductBoard for customer insights

Acceptance Criteria

This can be split into sub-issues, or expanded upon

• Users see clear warnings on the workspace page when wildcard is not configured
• Template admins see clear warnings when they use a coder_app that requires a subdomain, but wildcard is not configured
• Our documentation mentions the importance of wildcard domains during the install / set up of Coder
• Users see a clear build or runtime warning when their coder_app exceeds the DNS character limit Coder apps with long hostname fail without explanation #15178