Symptom: picking a model in the Desktop composer for the primary chat
silently rewrote config.yaml (model.default + model.provider) as the
profile default, ignoring model.persist_switch_by_default. A throwaway
pick that resolved to e.g. openai-api (no key) left the profile with an
unusable default on the next launch (#90235).
Root cause: 7d96537bc8 (#86414) made use-model-controls.ts send --global
for every primary-tile pick so a fresh profile would get a persisted
provider instead of falling through to a leftover OPENAI_API_KEY env var.
That put a persistence policy in the client, contradicting the
server-side rule /model uses (resolve_persist_behavior).
Fix:
- resolve_persist_behavior gains one rule, ahead of the --provider
session-only rule: when neither model.default nor model.provider is
configured yet, persist. This preserves #86414's first-pick motivation
for CLI, gateway and Desktop alike. With a default configured, a plain
pick is session-only unless --global / persist_switch_by_default.
- Desktop primary-tile picks send no scope flag and let the gateway decide.
Secondary tiles and MoA presets still send --session.
- /model help text in cli.py said "(persists)"; it now matches reality and
lists --global.
- Docs: desktop.md picker note + slash-commands /model row.
Tests: test_first_pick_persists_then_session_only (fails on main), and the
existing use-model-controls vitest updated to assert the flag-less request.
aaa34b0e08