ACP session/load response omits sessionId — breaks resume for Agent of Empires and any spec-compliant ACP client

Bug

The ACP session/load handler in packages/opencode/src/acp/service.ts (line ~211, loadSession) returns { configOptions } but omits sessionId from the response. The ACP spec requires sessionId in the session/load result (the newSession handler correctly returns { sessionId, configOptions }).

Impact

Agent of Empires (aoe) v1.13.1+ sends a spec-compliant session/load { sessionId, cwd, mcpServers } request, receives a response with no sessionId, and rejects it: session/load response missing sessionId. It then silently falls back to session/new, so every worker restart forks a fresh session and loses the transcript context — the dashboard shows "Agent finished but didn't notify the daemon; restarting worker" and the old conversation never resumes.

Repro (raw ACP probe)

// opencode acp --cwd <dir>; send initialize, then:
session/load { sessionId: "ses_...", cwd: "/path", mcpServers: [] }
// → 200 result: { "configOptions": [...] }   ← sessionId missing

Verified against opencode 1.18.18 and current dev.

Fix

In loadSession, return sessionId alongside configOptions:

return {
  sessionId: state.id,
  configOptions: configOptions(...),
}

(state.id === params.sessionId — the response just needs to echo it back per spec.)