Bug: SSE event streams omit standard event IDs

[TheLoroXD]

Description

The /event and /global/event SSE responses include event IDs inside the JSON payload, but do not emit the standard SSE id: field. Clients using browser/EventSource-style reconnects therefore cannot send a meaningful Last-Event-ID after reconnecting.

This is a narrower bug than full replay support: even before adding a replay buffer, the stream should expose the event ID through the SSE framing.

Plugins

None

OpenCode version

dev

Steps to reproduce

1. Start OpenCode server.
2. Connect to /event or /global/event.
3. Inspect the raw SSE frames.
4. Observe data: frames containing payload IDs, but no SSE id: line.

Screenshot and/or share link

N/A, server-side SSE framing issue.

Operating System

macOS / Linux

Terminal

N/A

Related to #25657 and #19584, but scoped only to emitting standard SSE event IDs.

[github-actions]

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