Persistent User Model Setting Failure in Configuration i want to DEFAULT to SONNET not YOUR FORCED DEFAULT

Bug Description
---
Title: Default model setting not persisting - reverts to system default instead of user-chosen Sonnet
This used to work perfectly and now it doesn't now it goes to your default and not my default and in the settings I've got that I want to go to SONNET however you're update or whatever you've done again has now broken the system so I'm forced to use what you want not what I want

Description:
I have set Sonnet as my default model in the settings, but Claude Code ignores this setting and chooses its own default model when I open it. The setting appears to be saved in the
interface but doesn't actually take effect. This keeps happening after updates and is extremely frustrating.

Steps to Reproduce:

1. Set Sonnet as default model in Claude Code settings
2. Setting shows as saved/configured in the settings interface
3. Close and reopen Claude Code
4. System uses its own default model instead of my chosen Sonnet

Expected Behavior:
Claude Code should use my configured Sonnet model as the default when opening

Actual Behavior:
Claude Code ignores my user setting and uses the system default model instead

Environment:

• OS: macOS (Darwin 24.6.0)
• Claude Code version: [current version]

This is a recurring issue that happens after updates and makes the default model setting completely useless.

Environment Info

• Platform: darwin
• Terminal: iTerm.app
• Version: 1.0.86
• Feedback ID: 9e2c0d0a-9eb4-4edf-a679-3164e6b41fd9

Errors

[{"error":"Error: Invalid settings\n    at sF4 (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:757:30073)\n    at r02 (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:757:30795)\n    at tF4 (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:757:32600)\n    at SL (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:757:32984)\n    at c2 (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:757:32916)\n    at lN2 (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:777:3496)\n    at file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:1981:290\n    at Q (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:677:13339)\n    at bT8 (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:3499:10173)\n    at file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:3542:1373","timestamp":"2025-08-21T04:03:56.745Z"},{"error":"Error: Invalid settings\n    at sF4 (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:757:30073)\n    at r02 (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:757:30795)\n    at wI (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:757:31567)\n    at Ps (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:739:1521)\n    at Uq1 (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:739:1484)\n    at Bj2 (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:848:12199)\n    at UP0.<anonymous> (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:3512:118)\n    at UP0.B [as _actionHandler] (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:667:528)\n    at file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:671:3127\n    at UP0._chainOrCall (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:671:1694)","timestamp":"2025-08-21T04:03:56.834Z"},{"error":"Error: Invalid settings\n    at sF4 (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:757:30073)\n    at r02 (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:757:30795)\n    at wI (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:757:31567)\n    at Ps (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:739:1521)\n    at Uq1 (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:739:1484)\n    at Bj2 (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:848:12199)\n    at UP0.<anonymous> (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:3512:118)\n    at UP0.B [as _actionHandler] (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:667:528)\n    at file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:671:3127\n    at UP0._chainOrCall (file:///Users/greg/.claude/local/node_modules/@anthropic-ai/claude-code/cli.js:671:1694)","timestamp":"2025-08-21T04:03:56.834Z"},{"error":"RangeError [ERR_CHILD_PROCESS_STDIO_MAXBUFFER]: stdout maxBuffer length exceeded\n    at Socket.onChildStdout (node:child_process:482:14)\n    at Socket.emit (node:events:507:28)\n    at Socket.emit (node:domain:489:12)\n    at addChunk (node:internal/streams/readable:559:12)\n    at readableAddChunkPushByteMode (node:internal/streams/readable:510:3)\n    at Readable.push (nod

Note: Error logs were truncated.