fix(session): bound html retry messages

[fengjikui]

Issue for this PR

Closes#35640

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

When a retryable provider error includes an HTML response body, keep the retry status message short instead of surfacing the raw HTML. The existing retry decision is unchanged; only the displayed message is bounded for HTML provider failures.

How did you verify your code works?

• bun test --timeout 30000 test/session/retry.test.ts
• bun run typecheck from packages/opencode
• bun run lint from the repo root
• git diff --check

Screenshots / recordings

N/A, retry status text only.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

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