feat: base path support

[hsteude]

Add support for running OpenCode behind a reverse proxy with a configurable base path prefix (e.g., /myapp/)

Fixes this issue.

Why

When deploying OpenCode with path-based routing, the application needs to serve assets and handle routing under a URL prefix. Without this, OpenCode can only run at the root path.

What it does

• Adds --base-path CLI option, OPENCODE_BASE_PATH env var, and server.basePath config
• Rewrites HTML/JS/CSS responses at runtime to include the base path
• Wraps history.pushState/replaceState to prepend base path to URLs

Design decisions

Runtime rewriting: We rewrite content at runtime because the frontend is proxied from app.opencode.ai and we don't control the build.

Regex-based Vite patching: Vite bakes the base path into a function at build time (function(t){return"/"+t}). Since we don't know the base path until runtime, we patch this via regex. It's not great, but the only alternative would require rebuilding the frontend for each deployment.

Double mounting: The app is mounted at both basePath AND / because some reverse proxies strip the path before forwarding. Without this, requests would 404.

No CSP with basePath: We inject inline scripts for the history wrapper, which is incompatible with strict CSP.

Feedback and Ideas are welcome :)

[github-actions]

Hey! Your PR title Feature/base path support doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

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

No duplicate PRs found

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[PhantomYdn]

Really looking for this PR to be merged! Thank you, @hsteude. Dear maintainers - please check/merge.

[PhantomYdn]

@hsteude I was playing around with your PR. Seems that additional fix is needed. When I run from a custom base path I see the following error:

Error: Could not connect to server. Is there a server running at `http://localhost:8080`?
    at l (http://localhost:8080/my/custom/base/assets/index-DT_hEdoD.js:1728:18349)

[hsteude]

@hsteude I was playing around with your PR. Seems that additional fix is needed. When I run from a custom base path I see the following error:

Error: Could not connect to server. Is there a server running at `http://localhost:8080`?
    at l (http://localhost:8080/my/custom/base/assets/index-DT_hEdoD.js:1728:18349)

@PhantomYdn : Thanks for taking a look into this, good catch! I didn't realize because we tested with our own internal build where the basePath fix is baked in at build time. Added a commit that fixes the regex pattern. Also rebased on dev. Would you mind checking again if it works for you now?

[PhantomYdn]

@hsteude It partially helped, but not yet fully solve the issue. The fonts (may be other resources as well) are loaded through JavaScript and still assume hardcoded paths like /assets/. If it will help - I have patched version of base-path.ts with which everything works for me. But(!) it's solving the problem in a little bit ugly way: patching JS on the fly.
base-path.ts

[PhantomYdn]

@hsteude I have solved this problem here: https://github.com/SkyNetCMS/opencode. There are few complexities, like availablility of frontend beyond reverse proxy with fixated opencode version (apparantly "opencode web" proxy all requests to app.opencode.ai and it's posslb to have case when opencode is older and not compatible with frontend)