Safari/WebKit dropped the AI chat answer stream mid-turn ("Load failed",
shown as "Lost connection to the server") while Chrome/Firefox were fine.
Two Safari-specific causes: (1) during model think/tool gaps the UI-message
SSE stream emits no bytes and WebKit aborts a non-progressing fetch far more
aggressively than Chrome; (2) the AI SDK sets a hop-by-hop `Connection:
keep-alive` header which is illegal on HTTP/2 — Chrome/Firefox ignore it,
Safari rejects the whole response. Earlier commits only improved the error
text, never the drop itself.
Add apps/server/src/core/ai-chat/sse-resilience.ts with two helpers wired into
both stream paths (authenticated + public share):
- startSseHeartbeat: writes a `: ping` SSE comment every 15s (ignored by the
client's EventSourceParserStream) so bytes keep flowing; unref'd timer,
guarded writes, auto-clear on finish/close.
- stripStreamingHopByHopHeaders: wraps writeHead once to drop Connection/
Keep-Alive before the head is sent, so they can never leak into an HTTP/2
response.
Add sse-resilience.spec.ts (7 tests). tsc + eslint clean.
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