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MCP Server Fails to Initialize Behind Corporate Proxy (TypeError: fetch failed) #1460

@zareefislam

Description

@zareefislam

Via GitHub support:

Trying to run the Copilot MCP Server inside Visual Studio Code (version 1.105.1)

Output logs show:

2025-10-30 09:11:28.332 [info] Connection state: Running
2025-10-30 09:11:33.339 [info] Waiting for server to respond to initialize request...
2025-10-30 09:11:38.340 [info] Waiting for server to respond to initialize request...
2025-10-30 09:11:39.112 [info] Connection state: Error Error sending message to https://api.githubcopilot.com/mcp/: TypeError: fetch failed

When testing the same endpoint manually with curl, can successfully establish a proxy tunnel

Despite this, when the MCP server starts, no network traffic leaves the machine (confirmed via network trace).

Reachability

github.com: HTTP 200 - OK
api.github.com: HTTP 200 - OK
proxy.enterprise.githubcopilot.com: HTTP 200 - OK
api.enterprise.githubcopilot.com: HTTP 200 - OK
telemetry.enterprise.githubcopilot.com: HTTP 200 - OK
exthost.log

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