[BUG] MCP HTTP connection hangs indefinitely at 'basic HTTP connectivity' pre-check (custom CA-merge agent) — external tools connect instantly

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Every connection attempt to the Meta Ads MCP server (HTTP transport, https://mcp.facebook.com/ads) hangs for the full configured timeout. Debug logs show the internal "basic HTTP connectivity" pre-check never returns — despite the server, DNS, TLS, and OAuth token all independently verified working via direct Graph API calls. Root cause isolated to Claude Code's own compiled binary's custom CA-cert-merging HTTPS agent; not fixable from this machine.

What Should Happen?

The MCP server should connect within normal time — consistent with how other tools (direct Invoke-RestMethod calls to the same Graph API endpoints, other stdio MCP servers) reach it instantly.

Error Messages/Logs

mcp-tool-discovery-bug-log.txt

#86674 report — same evidence applies here

Re-confirmed live today (2026-08-14): claude mcp list still returns meta-ads: https://mcp.facebook.com/ads (HTTP) - × Failed to connect — MCP server "meta-ads" connection timed out after 90000ms

Steps to Reproduce

1. Configure the meta-ads MCP server (HTTP transport) with a valid OAuth token.
2. Run claude mcp list or attempt any meta-ads tool call.
3. Connection hangs at the "basic HTTP connectivity" pre-check for the full 90000ms timeout, then fails.
4. Meanwhile, direct Graph API calls to the same account/token via PowerShell (Invoke-RestMethod) succeed instantly, and other stdio MCP servers (Playwright, Firecrawl) connect without issue — isolating the fault to this server's HTTP-transport handling specifically.

Claude Model

claude-sonnet-5

Is this a regression?

Yes. Unlike #86674, this one did work originally — first connected successfully via .mcp.json, confirmed with "list my Meta ad accounts" returning real data. It broke at some point after that and has been non-functional since, with meta-connect.ps1 (direct Graph API) as the working fallback.

Last Working Version

Not captured at the time — it worked earlier in this same setup process (before 2026-08-13), but the exact Claude Code version at that point wasn't logged. Worth noting as "unknown, but confirmed working prior to this timeframe" rather than a specific build.

Claude Code Version

2.1.231 (current — confirmed still broken on this version as of today)

Platform

VS Code extension

Operating System

Windows 11 Pro, build 10.0.26200

Terminal/Shell

Windows PowerShell 5.1

Additional Information

Distinct from #86674: this server never finishes connecting (hangs at pre-check); #86674's servers connect fine but expose no tools. meta-connect.ps1 / direct Graph API PowerShell scripts remain the confirmed working fallback in the meantime.