V2 event streams can stall with Kaspersky without an SSE Accept header

Description

On Windows with Kaspersky 21.26 enabled, the V2 CLI can remain on Restarting service... for minutes even though /api/health responds normally. The generated Promise SSE client does not set Accept: text/event-stream, and the initial /api/event response can be delayed beyond the CLI's two-second connection deadline.

I compared the same authenticated requests against one running 2.0.3 backend, without restarting it or changing its configuration:

The request-header-dependent delay also reproduces with a separate Node HTTP server/client, without OpenCode plugins. This identifies a compatibility problem with the enabled security software, not a particular internal Kaspersky module.

The EventSource specification says user agents may set this header, not that it is mandatory. Setting it by default for Promise SSE requests would improve interoperability; explicit caller headers should remain respected. SvelteKit has a matching Kaspersky report.

OpenCode version

Observed in 2.0.2 and 2.0.3. The default is still missing on v2 at 7a31b5c0f76ce1c06befacc09b47b4fc3c71c408, in packages/httpapi-codegen/src/index.ts and packages/client/src/promise/generated/client.ts.

Steps to reproduce

1. On an affected Windows/Kaspersky setup, start the V2 CLI and observe repeated connection timeouts while the backend remains healthy.
2. Compare authenticated streaming GET requests to the same /api/event endpoint with the default Accept and with Accept: text/event-stream.
3. The explicitly identified SSE request receives server.connected promptly; the default request can stall until later traffic arrives.

Operating System

Windows x64