Windows: context window stuck at 200K instead of 1M for Opus 4.6

Description

Same account, same CLI version (2.1.88), but Windows gets a 200K context window while Mac gets 1M for Claude Opus 4.6.

Details

• CLI version: 2.1.88 (latest) on both machines
• Model: claude-opus-4-6
• Mac: 1M context window, MCP tools ~19K tokens
• Windows: 200K context window, MCP tools ~190K tokens
• OS: Windows 11 Pro 10.0.26200
• Clients tested: Antigravity (desktop app) and CLI in Windows Terminal — both show 200K

Root cause identified

The server-side feature flag tengu_hawthorn_window is set to 200000 on Windows while it's 1000000 on Mac for the same account.

Additionally, tengu_defer_all_bn4 and tengu_defer_caveat_m9k are false on Windows, causing MCP tool definitions to consume ~190K tokens instead of being properly deferred (~19K on Mac).

Manually editing ~/.claude.json to set the correct values has no effect — the server overwrites them on session start.

Expected behavior

Same account should get the same feature flags (1M context window, deferred MCP tools) regardless of OS.

Steps to reproduce

1. Install Claude Code 2.1.88 on Windows
2. Run claude or use Antigravity
3. Run /context — shows 200K
4. Compare with same account on Mac — shows 1M