Desktop active-session picker calls already pass a session_id, but the gateway's model switch persistence is controlled by parsed model flags. Add --session so the shared parser keeps live-session selections, including MoA virtual provider presets, out of profile config.yaml.
Constraint: config.set model values are parsed by hermes_cli.model_switch before persistence is decided.
Rejected: backend special-case for desktop session_id | it would duplicate existing --session semantics and widen the gateway surface.
Confidence: high
Scope-risk: narrow
Directive: Keep desktop model picker active-session switches explicit with --session; do not rely on session_id alone for persistence.
Tested: npm run test:ui -- src/app/session/hooks/use-model-controls.test.tsx src/app/shell/model-menu-panel.test.tsx
Tested: npm run typecheck
Tested: git diff --check
Not-tested: full pytest suite; change is desktop TypeScript/UI routing only.
ce5c1f9f79