tui: client polls http://localhost:8000/health every 30s from any project

Summary

While any OpenCode TUI client is running, something inside the client sends
GET http://localhost:8000/health every 30 seconds to whatever service happens
to be listening on port 8000 on localhost — regardless of working directory or
project. The polling continues indefinitely even though the endpoint returns 404,
is not visible in opencode logs, and cannot be traced to any config, plugin, or
MCP server.

Environment

• opencode version: 0.0.0-beta-18269
• OS: Darwin 27.0.0 (macOS, arm64)
• Terminal: tmux (TERM=xterm-256color, COLORTERM=truecolor)
• Shell: /bin/zsh
• Install/channel: beta (~/.local/lib/node_modules/@opencode-ai/cli)
• Active plugins: none configured; only MCP server is chrome-devtools (local npx)

Reproduction

1. Start any local HTTP server on port 8000 that logs requests (in my case a
   FastAPI/uvicorn app) with a middleware that logs path + User-Agent.
2. Start the background service only (opencode2 serve --service equivalent):
   no polling occurs.
3. Kill all opencode processes: polling stops immediately.
4. Start opencode2 (TUI/client): polling begins within seconds.

Observed server-side log:

11:55:19 /health from 127.0.0.1:58849 UA='opencode2/0.0.0-beta-18269'
INFO:     127.0.0.1:58849 - "GET /health HTTP/1.1" 404 Not Found
11:55:49 /health from 127.0.0.1:58885 UA='opencode2/0.0.0-beta-18269'
INFO:     127.0.0.1:58885 - "GET /health HTTP/1.1" 404 Not Found

Requests arrive exactly ~30s apart, indefinitely, from any directory (tested in
the project dir and in an unrelated neutral directory).

Additional observations:

• lsof -i :8000 shows the socket owned by the serve --service process
  (i.e., an in-process HTTP client of the server, not a spawned shell/curl).
• Nothing appears in ~/.local/share/opencode/log/opencode.log when the
  requests fire.
• No config file, plugin, MCP config, skill, agent definition, or env var on
  the machine references port 8000 or /health.
• On one occasion uvicorn reported request.client is None for this request,
  which normally doesn't happen for plain TCP connections.
• The polled endpoint returns 404 and polling does not back off or stop.

Expected Behavior

If this is intentional dev-server detection/probing, it should be:

• documented and logged,
• stopped or backed off after repeated non-2xx responses,
• restricted to relevant ports/projects, and ideally configurable/disable-able.

If it's not intentional, the client should not send unsolicited requests to
arbitrary local services.

Actual Behavior

Undocumented, unlogged, unstoppable 30s polling of localhost:8000/health
whenever a TUI client is connected, hitting unrelated local services.

Additional Context

Isolation experiments performed:

Happy to run further diagnostics on request.