[BUG] spawn ENAMETOOLONG on every local session - Windows 11, MS Store build 1.20186.1

Environment

• Claude Desktop 1.20186.1 (Microsoft Store install), Windows 11
• Error: spawn ENAMETOOLONG on every local session (Cowork/Code). Remote/cloud sessions work fine on the same account and machine.

Log evidence (%APPDATA%\Claude\logs\main.log):

[error] [CCD] Failed to warm session local_1155894d-...: spawn ENAMETOOLONG
    at ChildProcess.spawn (node:internal/child_process:441:11)
    at _U.spawnLocalProcess (...app.asar\.vite\build\index.chunk-CvbeGVMj.js:80:2979)

What I ruled out

• Reduced local MCP extensions from 48 enabled to only 4 (filesystem, windows-mcp, chrome-control, desktop commander) + full app restart -> error persists.
• Reduced enabled connectors -> error persists.
• App is up to date.

Assessment
The command line built by spawnLocalProcess exceeds the Windows CreateProcess limit regardless of local extension/connector count, so the oversized payload appears to come from what the app injects server-side (system prompt / account model config). Possibly related: #64551, #72725, #60669.

Impact: local sessions are completely unusable on this account/machine.