Simplify pass on the picker-persist coverage:
- Stub list_picker_providers + resolve_display_context_length so the
tests no longer make real outbound HTTP calls (OpenRouter catalog +
Ollama /api/show) during picker setup and confirmation rendering.
Runtime drops from ~11s to ~0.4s and the tests are now deterministic.
- Collapse the two positive persist cases into one parametrize over the
config seed (nested-dict vs flat-string), asserting the nested-dict
invariant in both.
- Assert the in-memory session override is applied in the --session
case, closing a 'passes for the wrong reason' gap (config untouched
AND the switch still took effect).
- _FakePickerResult -> types.SimpleNamespace.
Mutation re-checked on the final test: both persist cases fail on
pre-fix slash_commands.py; the --session case passes on both.
Add regression coverage for the picker persist fix: drive the real
_handle_model_command with a fake picker-capable adapter that captures
the on_model_selected callback, fire a 'tap', and assert config.yaml is
written (bare /model), left untouched (--session), and that a flat-string
model: is coerced to a nested dict on a tap.
Mutation-checked: the persist and coercion assertions fail on pre-fix
slash_commands.py and pass on the fix.
