OpenCode Web Customization & Local Run Notes

Local Web UI (pointing at `/opencode`)

This uses the OpenCode web app from ~/misc/opencode/packages/app and points it at the Sandbox Agent OpenCode-compatible API. The OpenCode JS SDK emits absolute paths ("/global/event", "/session/:id/message", etc.), so any base URL path is discarded. To keep the UI working, sandbox-agent now exposes the OpenCode router at both /opencode/* and the root (/global/*, /session/*, ...).

1) Start sandbox-agent (OpenCode compat)

cd /home/nathan/sandbox-agent.feat-opencode-compat
SANDBOX_AGENT_SKIP_INSPECTOR=1 SANDBOX_AGENT_LOG_STDOUT=1 \
  ./target/debug/sandbox-agent server --no-token --host 127.0.0.1 --port 2468 \
  --cors-allow-origin http://127.0.0.1:5173 \
  > /tmp/sandbox-agent-opencode.log 2>&1 &

Logs:

tail -f /tmp/sandbox-agent-opencode.log

2) Start OpenCode web app (dev)

cd /home/nathan/misc/opencode/packages/app
VITE_OPENCODE_SERVER_HOST=127.0.0.1 VITE_OPENCODE_SERVER_PORT=2468 \
  /home/nathan/.bun/bin/bun run dev -- --host 127.0.0.1 --port 5173 \
  > /tmp/opencode-web.log 2>&1 &

Logs:

tail -f /tmp/opencode-web.log

3) Open the UI

http://127.0.0.1:5173/

The app should connect to http://127.0.0.1:2468 by default in dev (via VITE_OPENCODE_SERVER_HOST/PORT). If you see a “Could not connect to server” error, verify the sandbox-agent process is running and reachable on port 2468.

Notes

The web UI uses VITE_OPENCODE_SERVER_HOST and VITE_OPENCODE_SERVER_PORT to pick the OpenCode server in dev mode (see packages/app/src/app.tsx).
When running in production, the app defaults to window.location.origin for the server URL. If you need a different target, you must configure it via the in-app “Switch server” dialog or change the build config.
If you see a connect error in the web app, check CORS. By default, sandbox-agent allows no origins. You must pass --cors-allow-origin for the dev server URL.
The OpenCode provider list now exposes a sandbox-agent provider with models for each agent (defaulting to mock). Use the provider/model selector in the UI to pick the backing agent instead of environment variables.

Dev Server Learnings (Feb 4, 2026)

The browser cannot reach http://127.0.0.1:2468 unless the web UI is on the same machine. If the UI is loaded from http://100.94.102.49:5173, the server must be reachable at http://100.94.102.49:2468.
The OpenCode JS SDK uses absolute paths, so a base URL path (like http://host:port/opencode) is ignored. This means the server must expose OpenCode routes at the root (/global/*, /session/*, ...), even if it also exposes them under /opencode/*.

CORS must allow the UI origin. Example:

./target/debug/sandbox-agent server --no-token --host 0.0.0.0 --port 2468 \
  --cors-allow-origin http://100.94.102.49:5173

Binding the dev servers to 0.0.0.0 is required for remote access. Verify ss -ltnp | grep ':2468' and ss -ltnp | grep ':5173'.
If the UI throws “No default model found”, it usually means the /provider response lacks a providerID → modelID default mapping for a connected provider.

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