fix(product-assistant): correctly establish a connection for streaming

[skoob13]

Problem

The assistant doesn't stream the response back to a client. There are two potential problems:

• I didn't use the standard of server-sent events, e.g. the data: prefix.
• The delay to a first chunk is longer now, so gunicorn kills the connections and buffers the input. Frontend receives the concatenated chunks.

Changes

• Implement the standard prefix for SSE and use the 900 bytes library for response parsing (https://github.com/rexxars/eventsource-parser). 500k downloads and no deps.
• Send an empty chunk right after the connection is received.

Does this work well for both Cloud and self-hosted?

No

How did you test this code?

Manual testing.

[github-actions]

Size Change: 0 B

Total Size: 1.15 MB

ℹ️ View Unchanged

Filename	Size
frontend/dist/toolbar.js	1.15 MB

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[Twixes]

Sounds good to me, though the Thread story is kaput

[Twixes]

Broken again 😅

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• webkit: 0 added, 0 modified, 0 deleted

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