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web_search fails with HTTP 504 Gateway Timeout at ~120s (remote GitHub MCP server gateway timeout) #5301
Description
Describe the bug
The built-in web_search tool fails intermittently (more than half of calls over the last ~9 days) with:
MCP server 'github-mcp-server': MCP request failed: Transport send error: Transport [...StreamableHttpClientWorker<...RawCapturingReqwestClient>...] error: unexpected server response: HTTP 504 Gateway Timeout: [HTML error page omitted]
Every failure happens at ~121s. Successful calls take between 32s and 115s. This points to a fixed 120s gateway timeout in front of the remote MCP endpoint (https://api.business.githubcopilot.com/mcp/readonly). The web search backend (Bing searches plus answer synthesis) often runs longer than that limit.
Evidence (from local ~/.copilot/session-state/*/events.jsonl, tool.execution_start → tool.execution_complete)
| Start (UTC) | Duration (s) | Result |
|---|---|---|
| 2026-10-22T00:53:58Z | 42.7 | OK |
| 2026-10-22T00:58:11Z | 42.4 | OK |
| 2026-10-22T12:39:50Z | 121.2 | 504 |
| 2026-10-22T12:42:42Z | 121.0 | 504 |
| 2026-10-23T18:04:13Z | 109.2 | OK |
| 2026-10-26T17:13:55Z | 87.1 | OK |
| 2026-10-27T17:06:36Z | 120.9 | 504 |
| 2026-10-28T19:36:13Z | 120.9 | 504 |
| 2026-10-28T19:38:52Z | 114.8 | OK |
| 2026-10-28T19:38:52Z | 120.8 | 504 |
| 2026-10-28T19:40:56Z | 120.9 | 504 |
| 2026-10-28T19:49:43Z | 121.1 | 504 |
| 2026-10-28T19:57:28Z | 42.3 | OK |
| 2026-10-28T19:59:53Z | 32.1 | OK |
| 2026-10-29T17:59:24Z | 120.9 | 504 |
| 2026-10-30T13:58:26Z | 121.0 | 504 |
That is 9 failures out of 16 calls, all at 120.8–121.2s.
Client-side causes ruled out
- No HTTP(S) proxy configured (env vars and
scutil --proxyare empty). - No TLS interception: the endpoint certificate is
CN=*.business.githubcopilot.com, issued by Sectigo. - Traffic is routed directly via the local network, not through the corporate VPN.
- The endpoint responds normally from the GitHub edge (
x-github-edge-region: iad,x-github-backend: Kubernetes). - Copilot CLI is on the latest version (1.0.105). It has no configurable timeout for this tool.
Expected behavior
web_search should complete reliably. Possible fixes:
- Raise the gateway/proxy timeout for the
web_searchtool on the remote MCP server above 120s. - Bound the backend search/synthesis time so it finishes and returns a (possibly partial) answer before the gateway limit.
- Stream progress or keep-alives over the streamable HTTP transport so the gateway does not close idle long-running requests.
Environment
- Copilot CLI 1.0.105, macOS (Apple Silicon), installed via Homebrew cask
- Plan: Copilot Business (
api.business.githubcopilot.com) - Remote MCP endpoint:
https://api.business.githubcopilot.com/mcp/readonly - Frequency: started roughly 2026-10-22 and occurs every day since
Activity