Replace the spinner-only UX with live log output during agent SDK
operations, matching the existing OpenCode plugin install experience.
Backend: emit structured events (started/log/completed/failed) via
EventEmitter during npm install and binary download. npm commands now
run with piped stdio for line-by-line streaming; binary downloads
report chunked progress every 1 MB.
Frontend: subscribe to `app://agent-install` events through a new
`useAgentInstallStream` hook and render a theme-aware log terminal
below the preflight checks panel.
Also fixes the install log container in both agent settings and the
OpenCode plugins modal: auto-scroll no longer shifts the outer page,
and colours now follow the active light/dark theme.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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