bug: treat transient certificate verification errors as retryable

Description

When OpenCode encounters an "unknown certificate verification error", it aborts immediately and causes the current task to lose progress. This typically happens during network transitions, such as switching VPNs or connecting to public Wi-Fi networks where a captive portal (like captive.apple.com) intercepts traffic with an untrusted or invalid TLS certificate.

Instead of crashing or aborting the entire session, this should be treated as a retryable network error, keeping the session alive so the user can retry once the connection stabilizes.

Plugins

None

OpenCode version

latest

Steps to reproduce

1. Start an OpenCode session and begin a task
2. Switch VPNs or connect to a public Wi-Fi with a captive portal
3. Let OpenCode trigger a network request during the transition
4. Observe the "unknown certificate verification error" and instant abort

Expected behavior

OpenCode should pause, preserve the current session and unsaved work, and retry the request once a valid connection is restored.

Actual behavior

It aborts immediately, wiping the current progress.

Screenshot and/or share link

Not available

Operating System

macOS

Terminal

Not specified