feat: add --base-path support for reverse proxy sub-path deployment

[superafun]

Problem

Users want to deploy the OpenCode Web UI behind a reverse proxy under a sub-path (e.g. https://example.com/opencode/), but all resource paths, API calls, WebSocket connections, and frontend routes are hardcoded to root /.

Solution

Allow the web UI to be served under a configurable base path at runtime — no rebuild required. This works for the embedded UI in pre-built binaries (the common deployment).

How it works

1. CLI flag: opencode web --base-path /opencode/ sets the base path
2. Server-side HTML injection: When returning index.html, the server injects the base path into a <script id="oc-base-path" type="application/json"> tag
3. Frontend reads it: Before the JS bundle executes, the frontend reads the injected value and uses it for:
   • API base URL (getCurrentUrl() in entry.tsx)
   • @solidjs/router base prop (so routes match correctly under the sub-path)
   • WebSocket URLs (via the existing terminalWebSocketURL which builds on the server URL)
4. Relative asset paths: Static asset references in index.html are changed to relative paths so the browser resolves them against the document URL

nginx config (strips prefix before forwarding)

location /opencode/ {
    proxy_pass http://localhost:4096/;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
    proxy_set_header Host $host;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto $scheme;
    proxy_read_timeout 86400;
}

Usage

opencode web --base-path /opencode/ --hostname 0.0.0.0

The base path defaults to / so existing deployments are unaffected.

Files changed

File	Change
packages/app/index.html	Relative asset paths + oc-base-path script tag
packages/app/src/entry.tsx	getBasePath() reads injected value; getCurrentUrl() uses it
packages/app/src/app.tsx	Pass basePath to @solidjs/router base prop
packages/opencode/src/cli/network.ts	Add --base-path CLI option
packages/opencode/src/cli/cmd/web.ts	Display URLs with base path
packages/opencode/src/server/server.ts	Pass basePath through ListenOptions
packages/opencode/src/server/routes/instance/httpapi/server.ts	Pass basePath to serveUIEffect
packages/opencode/src/server/shared/ui.ts	injectBasePath() rewrites HTML at runtime

Notes

• og:image / twitter:image keep their absolute / paths since social crawlers require absolute URLs and social preview images are not critical for sub-path deployments.
• The oc-base-path script uses type="application/json" so it is not executed by the browser and does not require a CSP hash.

[github-actions]

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[github-actions]

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

I found potential duplicate or related PRs:

1. PR feat(server): runtime base path support for reverse proxy deployments #28326 - feat(server): runtime base path support for reverse proxy deployments

   • feat(server): runtime base path support for reverse proxy deployments #28326
   • Directly addresses the same feature: runtime base path support for reverse proxy deployments

2. PR feat: base path support #7625 - feat: base path support

   • feat: base path support #7625
   • Older PR related to base path functionality

Both PRs appear to be addressing the same core issue of adding base path support for deploying the UI behind a reverse proxy. PR #28326 in particular seems to be tackling the exact same solution (runtime base path support). You should review these PRs to understand any prior work and avoid duplicating effort.

[superafun]

Closing as duplicate of #28326, which already implements runtime base path support with config file integration, server-side prefix stripping, redirects, 404 handling, and 18 unit tests. My PR covers the same core idea (server-side HTML injection + frontend reads it for Router base + API baseUrl) but #28326 is more complete.