Describe the bug
When a session-level model override is set (e.g. via session_status(model="opus")), starting a new session with /new or /reset does not clear the override. The next session starts on the overridden model instead of the configured default_model.

To reproduce

1. Set a model override in a session: e.g. type opus or call session_status(model="opus")
2. Start a new session with /new
3. Observe: session runtime shows the overridden model (e.g. anthropic/claude-opus-4-6) instead of the configured default

Expected behavior
/new and /reset should clear any session-level model overrides and start fresh with the configured default_model.

Workaround
Manually call session_status(model="default") at the start of the new session to reset the override.

Environment

• OpenClaw version: 2026.2.24 (df9a474)
• OS: macOS (Darwin 25.3.0, arm64)
• Default model configured: anthropic/claude-sonnet-4-6

Possible fix
When /new or /reset is processed, the session handler should explicitly clear any persisted model overrides (e.g. reset session.modelOverride to null / default before spawning the new session). Alternatively, session-level overrides could be stored ephemerally in-memory only and never persisted across session boundaries.