CLI/TUI cannot connect to a server URL with a path prefix (--server drops the base path) #50427

Description

opencode --server <url> fails when the server URL has a path prefix (e.g. behind a reverse proxy that routes /ws/<id>/ to an OpenCode server).

$ OPENCODE_PASSWORD=... opencode --server http://localhost:8888/ws/ca607df5
Error: Server at http://localhost:8888/ws/ca607df5 did not provide a compatible V2 health response
  [cause]: ClientError: UnexpectedStatus
    [cause]: Error: {"status":404}

The server is reachable: curl http://localhost:8888/ws/ca607df5/api/info returns {"version":"2.0.12",...}.

The generated promise client (packages/client/src/promise/generated/client.ts) builds request URLs with new URL(descriptor.path, options.baseUrl). Because every descriptor.path starts with /, the URL spec replaces the base path, so the request goes to http://localhost:8888/api/info instead of http://localhost:8888/ws/ca607df5/api/info. The Effect client uses HttpClientRequest.prependUrl and joins correctly, so only the promise client (CLI, TUI, web) is affected.

Plugins

None

OpenCode version

2.0.12

Steps to reproduce

1. Run opencode serve --port 4096 and put it behind any proxy that forwards /ws/x/* to it (or Bun.serve that strips the /ws/x prefix).
2. Run opencode --server http://localhost:<proxy-port>/ws/x.
3. Observe the 404 health error above, while curl <proxy>/ws/x/api/info succeeds.

Also reproducible without a proxy:

import { OpenCode } from "@opencode/client/promise"
const client = OpenCode.make({ baseUrl: "http://localhost:8888/ws/abc", fetch: async (input) => { console.log(String(input)); return Response.json({}) } })
await client.server.info() // logs http://localhost:8888/api/info

Screenshot and/or share link

No response

Operating System

macOS 26

Terminal

Ghostty