Surface terminal provider failure diagnostics

[TheGreatAxios]

Summary

• Surfaces sanitized provider diagnostics when terminal inference failures reach TUI, headless, and subagent presentation paths.
• Normalizes OpenCode Go response deltas and terminal error categories with provider-aware retry classification.
• Keeps terminal diagnostics attached to the correct send attempt without duplicate or stale notices.

Verification

• bun run check passes.
• Critic and Greybeard approve the terminal failure lifecycle and presentation behavior.

Fixes CL-7368

[linear-code]

CL-7368