feat: add OPENCODE_APP_URL for custom web app proxy

[jobrk]

Add environment variable to proxy the web UI to a custom URL instead of app.opencode.ai. This enables enterprises to host the web UI internally and have users run the local server pointing to the internal instance.

The code changes are simple and self explanatory

• OPENCODE_APP_URL overrides the default https://app.opencode.ai base for the web UI proxy
• The full URL pathname is now preserved, so hosting on a subpath (e.g. GitHub Pages at https://user.github.io/opencode) works correctly

Fixes #12445

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on the search results, I found two potentially related PRs:

1. feat(opencode): add HTTP/HTTPS proxy support (feat(opencode): add HTTP/HTTPS proxy support #10856)

   • feat(opencode): add HTTP/HTTPS proxy support #10856
   • Related because it also deals with proxy configuration for the application

2. feat: base path support (feat: base path support #7625)

   • feat: base path support #7625
   • Related because it handles custom URL path configuration, which is similar in intent to allowing custom web app proxying

These are contextually related to URL/proxy customization, though they may address different aspects of the feature. PR #12446 specifically focuses on proxying the web UI to a custom URL via an environment variable, which appears to be a more specific use case than the broader proxy support in #10856.

[jobrk]

@kikuchan hey this has been up for a while, could I help with anything to get this merged ?

[kikuchan]

I'm sorry, I think I can't. I'm just a developper, not a member of OC. besides, I'm not able to press the "approve" button on the screen...

I am a person who also want this PR is merged...

[kikuchan]

The subpath doesn't work for me yet...

Could you change it like this please?:

diff --git a/packages/opencode/src/server/server.ts b/packages/opencode/src/server/server.ts
index ad8b0efa5..9cf0cfeda 100644
--- a/packages/opencode/src/server/server.ts
+++ b/packages/opencode/src/server/server.ts
@@ -559,7 +559,8 @@ export namespace Server {

         // Proxy to configured app URL or default to app.opencode.ai
         const appUrl = Flag.OPENCODE_APP_URL ? new URL(Flag.OPENCODE_APP_URL) : new URL("https://app.opencode.ai")
-        const response = await proxy(`${appUrl.origin}${path}`, {
+        appUrl.pathname = appUrl.pathname.replace(/\/$/, '') + path;
+        const response = await proxy(appUrl, {
           ...c.req,
           headers: {
             ...c.req.raw.headers,

because .origin doesn't contain a subpath.