[BUG] Persistent ECONNRESET on Claude Code (desktop + CLI) on office network — resolved only by VPN or mobile hotspot, no local config changes made

### Preflight Checklist

- [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) 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?

Claude Code (both desktop app and CLI) fails consistently with API Error: Connection dropped (ECONNRESET) on our office Wi-Fi network, retrying up to 10 times before failing outright — this happens even on simple tasks like reading a single file. claude.ai chat works flawlessly on the same machine, network, and account throughout.

The issue started September 8, 2026 with no changes made on our side — I'm Head of IT/Technology for the organization and can confirm no firewall, proxy, or security policy changes were made in the relevant timeframe.

Critically: the same ISP (e&, Dubai, UAE) works fine via personal VPN, mobile hotspot, and home Wi-Fi — only this specific office circuit reproduces the failure. Basic curl tests to api.anthropic.com (including a streaming POST to /v1/messages) succeed cleanly with the connection staying intact, while actual Claude Code session traffic resets. This suggests the issue is specific to how Claude Code handles its connections (long-lived/streaming, possibly IP-based rather than hostname-based) rather than basic network connectivity or DNS.

This closely matches previously reported issues #2935 (Claude Code connecting to raw IPs instead of hostnames, breaking on networks with stricter policies — closed as not planned), #85979 (persistent ECONNRESET across multiple networks with all local causes eliminated), and #87424 (intermittent ECONNRESET with no VPN/proxy).

### What Should Happen?

Claude Code should maintain a stable connection to api.anthropic.com on this network, consistent with claude.ai's behavior on the same network and machine, and consistent with Claude Code's own behavior on VPN/hotspot/home Wi-Fi using the same ISP.

### Error Messages/Logs

```shell
API Error: Connection dropped (ECONNRESET)
✻ Cooked for 2m 52s

Reading device-storage.ts
file_path: /Users/[USER]/Sites/meeting-scheduler-monorepo/apps/kiosk/src/lib/device-storage.ts
🔴 Request failed · Retrying (5/10) · 35s

Diagnostic curl output (connection succeeds, for contrast):
* SSL certificate verify ok.
* using HTTP/2
* [HTTP/2] [1] OPENED stream for https://api.anthropic.com/
< HTTP/2 404
* Connection #0 to host api.anthropic.com left intact

* upload completely sent off: 121 bytes
< HTTP/2 401
{"type":"error","error":{"type":"authentication_error","message":"x-api-key header is required"}}
* Connection #0 to host api.anthropic.com left intact

DNS already set to 8.8.8.8 — not a resolution issue.
```

### Steps to Reproduce

Connect to office Wi-Fi (e&, Dubai, UAE)
Run any Claude Code task, including simple file reads (e.g., reading a single source file)
Observe API Error: Connection dropped (ECONNRESET), with retry counter climbing (e.g. "Retrying (5/10)")
Task eventually fails after exhausting retries
Compare: enable personal VPN, or switch to mobile hotspot (same ISP, e&) — task completes successfully with no errors
Compare: curl -v https://api.anthropic.com/ and curl -v -N https://api.anthropic.com/v1/messages on the same failing network — both complete cleanly with connection intact, no reset

### Claude Model

Sonnet (default)

### Is this a regression?

Yes, this worked in a previous version

### Last Working Version

_No response_

### Claude Code Version

2.1.236 (Claude Code)

### Platform

Anthropic API

### Operating System

macOS

### Terminal/Shell

iTerm2

### Additional Information

This was working until 7th September.

No source file or test is named. First reproduce on the office Wi-Fi, then compare Claude Code with VPN, hotspot, and home Wi-Fi while reviewing the connection behavior for session traffic; use the successful curl and streaming POST results as the baseline. Done means Claude Code completes the same task reliably on the office network without ECONNRESET retries.

索引モデルが issue の本文から書いたものです。