[Bug] Claude Code Desktop bundled CLI connection failures (ECONNRESET) — npm CLI unaffected

Bug Description

Bug Report: Persistent ECONNRESET in Claude Code Desktop (Windows) — CLI on same machine unaffected

Summary

Since the Claude desktop app updated to 1.25927.0.0 on 2026-08-05, Claude Code sessions
launched from the desktop app fail with repeated ECONNRESET errors, retrying with exponential
backoff until they exhaust and give up. The update to 1.26832.0.0 on 2026-08-07 did not
fix it.

The key signal: the npm-installed Claude Code CLI v2.1.224 runs flawlessly on the same machine,
same network, same account, at the same time. Only the desktop app's bundled Claude Code
(2.1.221, then 2.1.222) fails. This isolates the fault to the desktop app build rather than the
local environment or network.

User-visible symptoms:

• Banner: "Connection problem — Check your internet connection, VPN, or proxy and try again."
• Inline: API Error: Connection to the API was lost (ECONNRESET). This is usually temporary — try again.

Environment

| Item | Value |
|---|---|
| OS | Windows 11 Home Single Language, 10.0.26200 |
| RAM | 13.94 GB (5.5 GB free during failures) |
| Desktop app | Claude 1.26832.0.0 (MSIX, C:\Program Files\WindowsApps) |
| App's bundled Claude Code | 2.1.221, then 2.1.222 — fails |
| npm CLI Claude Code | 2.1.224 (AppData\Roaming\npm), Node v24.11.1 — works |
| Network | Wi-Fi, Realtek 8821CE, 5 GHz 802.11ac, signal 100% |
| Proxy / VPN | None configured |

Version timeline vs. onset

From the Windows AppX deployment log:

| Date/time (local) | App version | Behavior |
|---|---|---|
| 2026-08-03 22:16 | 1.24012.11.0 | Working normally |
| 2026-08-05 21:07 | 1.25927.0.0 | Failures begin |
| 2026-08-06 19:42–19:59 | 1.25927.0.0 | 20 ECONNRESETs in ~6 min |
| 2026-08-07 15:28 | 1.26832.0.0 | Update applied — not fixed |
| 2026-08-07 15:37 | 1.26832.0.0 | ECONNRESET still occurring |

Error detail

Raw record from the session transcript:

{"type":"system","subtype":"api_error","level":"error",
 "error":{"message":"Connection error.",
          "formatted":"Unable to connect to API (ECONNRESET)",
          "connection":{"code":"ECONNRESET",
                        "message":"The socket connection was closed unexpectedly.",
                        "isSSLError":false}}}

Note isSSLError: false — this is not a TLS negotiation failure.

Reproduction pattern

Two consecutive bursts on 2026-08-06, each retrying with exponential backoff until exhausted
(times UTC; local = UTC+3):

Burst 1:  16:52:30, :32, :34, :38, :44, :55, 16:53:15, 16:53:54, 16:54:35, 16:55:15
Burst 2:  16:56:26, :28, :30, :34, :40, :49, 16:57:08, 16:57:41, 16:58:16, 16:58:56

Backoff intervals: 2s, 2s, 4s, 6s, 11s, 20s, 39s, 41s, 40s. Every retry failed. This
retry-to-exhaustion behavior is what makes the app unusable, not the individual resets.

Logging gap worth flagging: %APPDATA%\Claude\logs\main.log recorded only 5 of these
20 errors. Anyone diagnosing from main.log alone will badly underestimate severity. The
complete record is only in the session transcript at
~/.claude/projects/<project>/<session-id>.jsonl.

Local causes systematically ruled out

Each was tested directly, not assumed:

| Hypothesis | Test | Result |
|---|---|---|
| Proxy / VPN | Env vars + WinINET registry | None configured |
| DNS | Resolve-DnsName api.anthropic.com | Resolves correctly |
| TCP reachability | Test-NetConnection :443 | Succeeds |
| Connection stability | 10 consecutive HTTPS requests | 10/10 succeeded |
| Path MTU blackholing | DF-bit ping sweep 1372–1472 | Full 1500 passes, no fragmentation |
| Sustained throughput | 25 MB HTTPS download | Completed, 21.1 s |
| Upload throughput | 8 MB HTTPS POST | Completed, 6.5 s (9.89 Mbps) |
| Latency / packet loss | 20 pings to API IP | 0% loss, avg 48 ms |
| IPv6 misrouting | Interface + route inspection | No global IPv6, no default route — never attempted |
| Wi-Fi driver drops | WLAN event log correlation | 6 drops in 3 days, zero correlate with errors |
| Memory pressure | RAM + page file during failure | 5.5 GB free, page file idle (0.32/11 GB) |
| Electron event-loop stalls | Stall log vs. error timestamps | No correlation (nearest 3 min apart) |
| TLS failure | isSSLError flag | false |
| Context / payload size | Token usage in transcript | ~60K tokens — normal |
| Third-party TLS inspection | AV enumeration | Windows Defender only |

Expected vs. actual

Expected: Claude Code launched …
Note: Content was truncated.