[BUG] Desktop app "Can't reach your computer" — persists after ruling out every local network/OS cause

### 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?

Summary

The Claude Code Desktop app repeatedly shows "Can't reach your computer — it may be asleep or offline. This session will reconnect when it's back," despite the machine being awake, online, and every locally-checkable network/OS condition confirmed healthy. The trigger has escalated over the course of troubleshooting: it started appearing only when sending /resume, and now appears immediately whenever chat is opened, even right after a fresh sign-in.

Environment

macOS (Darwin 27.0.0)
Claude Code Desktop app: v2.110.0
Bundled claude-code CLI in Desktop app: v2.1.271
Bundled claude-code CLI in VS Code extension (unrelated, separate session, unaffected): v2.1.270
Standalone CLI on PATH: v2.1.183
Timeline of what triggered it

Banner first appeared intermittently in the background while a VS Code-started session was active and working fine.
Confirmed the Desktop app has a "Local" Session Manager tab that mirrors this VS Code session live (marked "Active") — so cross-client session visibility works; this wasn't the underlying problem.
Banner reproduced reliably when sending /resume in the Desktop app's prompt, in this same active session.
Ruled out the "old dead session" theory — banner does not appear when opening a genuinely stale session ("Resume session," 15h old); it's tied to /resume specifically, not session age.
Attempted sign-out/sign-in as a fix. This required signing in twice to continue the session (itself abnormal). Did not resolve the issue.
After re-signing in, the banner regressed further: it now appears immediately on opening chat, not just on /resume.

Diagnostics performed and ruled out (all confirmed healthy)

Check | Method | Result
-- | -- | --
Local session process alive | ps aux | Confirmed running, not crashed/zombied
General internet reachability | curl to google.com, api.anthropic.com (IPv4 + IPv6) | 200 OK, low latency
Exact backend endpoint Claude.app connects to | ping6 to 2607:6bc0::10 (the live ESTABLISHED connection's remote) | 0% packet loss, ~4ms avg latency across 8 packets
macOS Local Network permission | System Settings → Privacy & Security → Local Network | Claude listed and enabled
macOS Application Firewall | socketfilterfw --getglobalstate / --getblockall | Firewall disabled entirely — not a factor
Local listening sockets | lsof -iTCP -sTCP:LISTEN | No listener needed/expected — confirmed Claude.app's only connection is one outbound IPv6 HTTPS session to Anthropic's servers, no local server involved
System clock accuracy | sntp -sS time.apple.com | Accurate to within ~4ms — rules out TLS/auth token timing issues
System sleep/wake events | pmset -g log | No relevant sleep/wake event around incident times
Local Claude logs/telemetry | ~/Library/Logs/Claude/*, ~/.claude/telemetry/* | No matching entries for this incident

### What Should Happen?

The Desktop app should not report "Can't reach your computer" when the local machine, its network, and the underlying connection to Anthropic's own servers are all verifiably healthy. If this check is server-side, it should be re-validated against a fresh, correctly-scoped device/session token after sign-in — not left in a state where two sign-in attempts and a clean network still produce a false negative.

### Error Messages/Logs

```shell

```

### Steps to Reproduce

Have an active Claude Code session in the Desktop app.
Send /resume in the chat.
Observe "Can't reach your computer" banner, despite the session remaining otherwise functional.
Sign out and sign back in (may require two attempts).
Reopen chat — banner now appears immediately, without needing /resume.

### Claude Model

Sonnet (default)

### Is this a regression?

I don't know

### Last Working Version

_No response_

### Claude Code Version

$ claude --version 2.1.183 (Claude Code)

### Platform

Anthropic API

### Operating System

macOS

### Terminal/Shell

Terminal.app (macOS)

### Additional Information

_No response_

No repository file or test is identified. Start by reproducing the active-session /resume flow, then the sign-out/sign-in flow, while checking the mentioned Claude logs and telemetry paths for matching entries. Done means the app no longer shows the false connectivity banner when the machine and Anthropic connection are healthy.

Written by the indexing model from the issue text.