[FEATURE]: Base path / prefix routing support

[hsteude]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Use case

We'd like to integrate OpenCode as a feature into larger platforms, where it runs under a URL prefix (e.g., platform.com/opencode/) rather than at the root path.

Request

Add support for a configurable base path so OpenCode can be embedded into existing platforms and served alongside other applications under the same domain.

[github-actions]

This issue might be a duplicate of or related to existing issues. Please check:

• allow overriding web client deployment path / bundle web client with opencode binary. #6352: allow overriding web client deployment path / bundle web client with opencode binary - discusses deployment configuration and serving from non-root paths
• opencode web - thinks it is in root (/) path #6336: opencode web - thinks it is in root (/) path - addresses path handling in the web UI
• [FEATURE]: Allow for Custom Server URL on hosted web #6311: Allow for Custom Server URL on hosted web - related feature for server configuration

These issues touch on similar aspects of URL configuration and hosting OpenCode in larger platforms. Feel free to ignore if your specific use case isn't covered by these.

[LeonMueller-OneAndOnly]

For the usage with tailscale this would also be a very nice feature, so one can expose multiple services from one machine over tailscale.

I am referring to this feature of tailscale serve:
--set-path= Appends the specified path to the base URL for accessing the underlying service.

https://tailscale.com/docs/reference/tailscale-cli/serve

[Ark-kun]

I was doing similar work and I might have found a simple way (just 7 lines of code) to get most of that via VITE_BASE_URL. Would you mind taking a look? #18209

It does something a bit different - it bakes the prefix during the build. But this also makes it very easy to change at runtime or even via proxy. For example, you can set VITE_BASE_URL="XXX_OPENCODE_BASE_URL_XXX" and then even a transparent proxy can dynamically replace it on the fly as it serves compiled JS files.