V2 TUI: retry notice renders raw HTML from provider 503 #35640

Summary

The V2 TUI retry notice prints an upstream nginx HTML error page verbatim when Little Frank returns HTTP 503. The raw response consumes several lines and exposes transport-level markup instead of a concise provider-unavailable message.

Environment

• OpenCode version: V2 development build; exact build unavailable from the report
• OS: macOS (from reporter context)
• Terminal: tmux; underlying terminal unavailable
• Shell: Unavailable
• Install/channel: opencode2 development channel
• Active plugins: Unavailable
• Model: Little Frank (anomaly / OpenAI), medium variant

Reproduction

1. Use Little Frank in the V2 TUI.
2. Have the provider return an nginx 503 Service Temporarily Unavailable HTML response.
3. Wait for the session retry UI to render the scheduled retry.

Expected Behavior

Show a bounded, human-readable retry notice, for example: Retry attempt 3 scheduled: provider temporarily unavailable (HTTP 503).

The raw HTML response may remain available in logs or expandable diagnostics, but should not be printed inline by default.

Actual Behavior

The retry notice includes the complete HTML document:

Retry attempt 3 scheduled: Provider request failed with HTTP 503: <html>
<head><title>503 Service Temporarily Unavailable</title></head>
<body>
<center><h1>503 Service Temporarily Unavailable</h1></center>
<hr><center>nginx</center>
</body>
</html>
[provider.internal]

Additional Context

• Screenshot: https://discord.com/channels/1391832426048651334/1447692703549755466/1523867993472503900
• Observed at 2026-07-07 01:47 UTC.
• Related: HTML error pages from gateways/proxies produce unreadable terminal output #15406 fixed raw HTML error rendering for gateway/proxy errors in V1, and TUI should show when it is retrying #4089 tracked retry visibility. V2 should preserve the same sanitization/bounding behavior in its retry surface.
• This issue is presentation-specific; retry policy itself is tracked separately in V2: port V1 LLM retry policy into opencode #35002.