[BUG] "sonnet" model alias resolves to claude-sonnet-4-5 instead of claude-sonnet-4-6 (v2.1.97)

Description

In Claude Code v2.1.97, the "sonnet" model alias in settings.json resolves to claude-sonnet-4-5 when spawning subagents, even though claude-sonnet-4-6 is the latest available Sonnet model. The main session itself runs on claude-sonnet-4-6, but every subagent process is spawned with --model claude-sonnet-4-5 explicitly.

Steps to Reproduce

1. Set settings.json to "model": "sonnet"
2. Start a Claude Code session and run any task that spawns subagents
3. Run ps aux | grep "\.local/bin/claude" and inspect the --model flag on spawned subprocesses

Expected Behavior

The "sonnet" alias should resolve to the latest Sonnet model (claude-sonnet-4-6), consistent with how the main session is started.

Actual Behavior

Subagents are spawned with --model claude-sonnet-4-5:

/Users/harshils/.local/bin/claude --output-format stream-json --verbose --input-format stream-json --model claude-sonnet-4-5 --resume ... --disallowedTools ...

Impact

• Users unknowingly run subagents on an older, more expensive model
• The main session and subagents run on different model versions, which can cause inconsistent behavior
• Workaround: explicitly pin "model": "claude-sonnet-4-6" in settings.json

Environment

• Claude Code version: 2.1.97
• OS: macOS (Darwin 25.4.0)
• Shell: fish