[BUG] Unable to connect to API : TCP shows ESTAB but app reports ConnectionRefused on prompt input

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?

Fedora 42, kernel 6.18
Was working, last use was several weeks ago
64GB RAM, no proxy, no VPN
curl connects fine, ss shows ESTAB connections to 160.79.104.10:443
Auth token valid, login succeeds
SELinux permissive makes no difference
Both npm and standalone installer fail identically
Error: Unable to connect to API (ConnectionRefused) despite established TCP connections

What Should Happen?

Claude should respond to prompt

Error Messages/Logs

Steps to Reproduce

launch claude
enter Hello Claude --or any text

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.150

Platform

Anthropic API

Operating System

Other Linux

Terminal/Shell

Other

Additional Information

TCP is fully established — ss -tp shows 7 ESTAB connections to 160.79.104.10:443 while Claude Code reports ConnectionRefused. This rules out network/firewall as the cause and points to something in Bun's application layer above the socket.
Direct API curl works — token is valid, API responds, TLS handshake succeeds.
Environment:

Fedora 42, kernel 6.18.13-100.fc42
64GB RAM, no swap pressure
No proxy, no VPN, no custom SSL certs
SELinux set to Permissive — no change
IPv6 disabled in /etc/hosts — no change
Both npm install and standalone installer fail identically
NODE_OPTIONS=--dns-result-order=ipv4first — no change
CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC=1 — no change
SSL_CERT_FILE=/etc/pki/ca-trust/extracted/pem/tls-ca-bundle.pem — no change

Was working previously — stopped working on or around May 2026. No system changes on that date except earlyoom and Intel compute runtime/media driver installs (confirmed unrelated).
Debug log shows:

CA certs: Config fallback - globalEnv keys: , settingsEnv keys:
CLAUDE_CODE_ENABLE_TELEMETRY, CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC,
CLAUDE_CODE_ATTRIBUTION_HEADER
The CA cert fallback line may be significant — Bun may not be finding Fedora's CA bundle at /etc/pki/ca-trust/extracted/pem/tls-ca-bundle.pem even when explicitly set via SSL_CERT_FILE.

Version: 2.1.150 standalone installer. Also tested 2.1.120 via npm — same failure.

The CA cert fallback is the most actionable lead for Anthropic — it's the one thing in the debug log that's anomalous and hasn't been fully explained.