Issue

Claude Desktop Cowork tab fails to connect with "API Error: Connection error" while regular chat tab works perfectly.

Environment

• macOS Darwin 25.1.0
• Claude Desktop (latest version)
• Claude Code VM SDK version: 2.1.5

Symptoms

• Regular chat tab works perfectly
• Cowork tab fails with "API Error: Connection error"
• Issue persists after app restart and full computer restart

Error from logs (main.log)

2026-01-13 12:38:07 [error] Session initialization failed for local_c05e8141-a6d2-4106-b6b4-4ece86116fc9: net::ERR_CONNECTION_RESET
2026-01-13 12:38:07 [info] [EventLogging] Sending event: lam_session_initialization_failed | metadata: {
  failed_step: 'auth',
  error_message: 'net::ERR_CONNECTION_RESET',

2026-01-13 12:48:46 [error] Session initialization failed for local_7723f28c-4151-4bdd-a10c-6f551bebf022: net::ERR_CONNECTION_RESET
2026-01-13 12:48:46 [info] [EventLogging] Sending event: lam_session_initialization_failed | metadata: {
  failed_step: 'auth',
  error_message: 'net::ERR_CONNECTION_RESET',

VM logs show successful startup (claude_vm_node.log)

2026-01-13 13:14:56 [info] [VM:start] SDK installed, total startup time: 5500ms
2026-01-13 13:15:09 [info] [Spawn:vm] id=723598a6-71ef-428a-ab48-3c76f24d4a9a Spawn succeeded

Analysis

• VM initializes correctly
• MCP servers connect successfully
• Failure occurs specifically at the auth step during session initialization
• Connection is being reset (ERR_CONNECTION_RESET) when attempting to authenticate cowork sessions
• Regular chat authentication works, suggesting the issue is specific to the cowork/local agent mode auth endpoint

Network verification

• ping api.anthropic.com succeeds
• curl https://api.anthropic.com returns 405 (expected without auth)
• No VPN or network filtering software active

Suspected cause

Server-side issue with cowork session authentication endpoint.