Auto-compact errors when model overridden to claude-opus-4-6 on stable channel (2.1.25)

Description

After setting the model override to claude-opus-4-6 in ~/.claude/settings.json, auto-compact fails persistently across all sessions. This is on the stable channel (v2.1.25).

The model override is necessary because the stable channel (2.1.25) still defaults to Opus 4.5, even though Opus 4.6 has been released and appears as the default on other platforms (macOS, WSL) running newer versions from the latest channel.

Steps to reproduce

1. Be on Claude Code stable channel v2.1.25 (Windows)
2. Set "model": "claude-opus-4-6" in ~/.claude/settings.json
3. Use Claude Code normally until the conversation triggers auto-compaction
4. Auto-compact fails with errors

Expected behavior

• Auto-compaction should work correctly regardless of the model override
• Ideally, the stable channel should also default to Opus 4.6 now that it's GA

Environment

• Claude Code version: 2.1.25 (stable channel)
• Platform: Windows (MSYS_NT-10.0-26100 / MINGW64)
• Install method: native
• Model override: claude-opus-4-6

Additional context

• No issues existed on version 2.1.19 without the model override
• The stable npm dist-tag still points to 2.1.25, while latest is 2.1.37
• Opus 4.6 appears to default correctly on macOS and WSL (likely running newer versions from the latest channel)
• Removing the model override and relying on the default still gives Opus 4.5 on stable, so users who want 4.6 are forced into the override which triggers this bug