Description

After upgrading Query Service from 0.14.1 to 0.14.3, the WebSocket connection to Core fails with:

Mint.WebSocketError{reason: :extended_connect_disabled}

The QS health endpoint returns 503 because it can't establish the WebSocket stream to Core.

Environment

• Hosting: Fly.io (both Core and Query Service)
• Core: 0.14.3 — healthy, WebSocket endpoint works fine over HTTP/1.1
• Query Service: 0.14.3 — starts but health check returns 503
• Connection URL: wss://alphasigmapro-allsource-core.fly.dev/api/v1/events/stream

Root cause

The Mint HTTP client in QS 0.14.3 attempts an HTTP/2 extended CONNECT for the WebSocket upgrade. Fly.io's reverse proxy (and likely other proxies like Cloudflare, ALBs) does not support HTTP/2 extended CONNECT — only standard HTTP/1.1 Upgrade: websocket.

Verified that Core's WebSocket endpoint works correctly over HTTP/1.1:

curl -sv --http1.1 \
  -H "Connection: Upgrade" \
  -H "Upgrade: websocket" \
  -H "Sec-WebSocket-Version: 13" \
  -H "Sec-WebSocket-Key: dGVzdA==" \
  "https://alphasigmapro-allsource-core.fly.dev/api/v1/events/stream"

# Returns: HTTP/1.1 101 Switching Protocols ✓

Expected behavior

QS should connect to Core's WebSocket endpoint using HTTP/1.1 upgrade, as it did in 0.14.1.

Suggested fix

Either:

1. Configure the Mint WebSocket client to use :http1 protocol mode (not :http2)
2. Add a CORE_WS_PROTOCOL env var to let operators choose
3. Fall back to HTTP/1.1 when HTTP/2 extended CONNECT fails

Logs

[CoreWebSocketClient] Connection failed: %Mint.WebSocketError{reason: :extended_connect_disabled}, retry 16 in 28531ms
WebSocket reconnection attempt url="wss://..." attempt=16
GET /api/health → Sent 503

This repeats every ~30s indefinitely.

Workaround

Rolled back Query Service to 0.14.1 which connects successfully.