[Windows Desktop] Session error notification + sound replays on every launch (event backlog has no replay guard)

Summary

Every time I open OpenCode Desktop on Windows, a system notification pops up with an error sound:

会话错误
发生错误
(Session error / An error occurred)

This happens even when the current session is perfectly healthy, and it happens on every single launch.

Root cause (successor to #15302 and #28894)

This is the same bug reported in #15302 ("Desktop notification sound plays repeatedly upon opening") and #28894 ("[Windows Desktop] Open code notifying lots of session error when opened"). Both were auto-closed after 60 days of inactivity with the note "If the issue is still relevant please open a new one" — it is still relevant, so here it is.

The desktop client replays the event backlog on connect, and historical session.error events run through the same handler as live events — there is no replay guard — so every previously-errored session re-fires an OS notification + sound on each launch.

Evidence from my machine (~/.local/share/opencode/log/opencode.log)

Historical errors accumulate in the journal from ordinary usage:

• AbortError from streams interrupted at app close
• Provider API errors (AI_APICallError from an openai-compatible provider, "No payment method" from a misconfigured model, etc.)

Correlation sample from today:

timestamp=2026-08-21T14:50:11.278Z level=ERROR ... error=Aborted
timestamp=2026-08-21T14:50:11.281Z ... message=init count=...   <- new instance boots 3 ms later -> toast fires

Environment

• OS: Windows 11 (zh-CN locale)
• OpenCode Desktop: 1.18.20
• Setup: multiple providers (openai-compatible + openrouter), several plugins, local MCP servers

Current workaround

Settings → General → Sounds → Errors → Off. This stops the toast/sound but the underlying backlog replay is unfixed, and it also silences genuinely useful live error alerts.

Suggested fix

Same as proposed in #15302: tag backlog/replayed events and gate playSoundById(...) / OS notification calls on !isReplay in handleSessionError (and the idle/permission handlers). Replayed events should still appear in the notification list, just without re-alerting.