Solution for 5f34ff07-8f22-4a9d-a0e9-100e34610021: Keep keepAliveMs at the default 15000 ms or set it lower than the tightest idle

## Cause Without frequent SSE comment bytes, undici client body timeouts and HTTP intermediaries treat the stream as idle and terminate it. ## Steps 1. Confirm client log shows 'SSE stream disconnected: TypeError: terminated' during an idle stretch of an open SSE stream. 2. On the server transport or createMcpHandler, verify keepAliveMs is not 0 and is below proxy/LB idle limits (default 15000). 3. If an intermediary enforces a shorter idle window, reduce keepAliveMs accordingly. 4. Retry the long tool call and monitor whether the SSE stream stays connected through idle periods. ## Expected result Periodic keepalive comments prevent premature termination; the SSE stream remains connected through idle portions of long tool execution. ## Misleading approaches - Disabling keepalive heartbeats to reduce traffic while using long-lived SSE. - Only increasing client timeouts without server-side keepalive when the proxy idle limit is the bottleneck. ## Limitations - Network path idle limits must be measured per deployment; defaults may not suffice behind aggressive proxies. - Other disconnect causes (auth, server crash) produce different errors. ## Unknowns - Exact idle timeout of each proxy or cloud load balancer in a given deployment. ## Evidence claims - (documented_platform_behavior) Default SSE keepalive comments are sent every 15 seconds to prevent idle termination. — https://raw.githubusercontent.com/modelcontextprotocol/typescript-sdk/7f7a94c22017e121a960e071bb50ec75e34450bd/docs/troubleshooting.md - (documented_platform_behavior) keepAliveMs on the transport or createMcpHandler controls the heartbeat interval; 0 disables heartbeats. — https://raw.githubusercontent.com/modelcontextprotocol/typescript-sdk/7f7a94c22017e121a960e071bb50ec75e34450bd/docs/troubleshooting.md