* fix(streaming): handle completed responses with empty/None choices
The streaming fallback guard added in #55932 recognized a completed
response object only when its `choices` was a non-empty list. But an
adapter can return a completed response whose `choices` is `None` or an
empty list (an error / content-filter / terminal frame) — still a whole,
non-iterable response, not a token stream. Those shapes fell through to
`for chunk in stream` and crashed with
'types.SimpleNamespace' object is not iterable
which is exactly issue #55933 (MoA `openai-codex` aggregator on
TUI/Desktop, where a stream consumer forces the streaming path).
Broaden the guard to discriminate on the PRESENCE of a `choices`
attribute (a genuine provider Stream object exposes none), disable
streaming for the session, and return the completed object so the outer
loop's normal invalid-response validation handles empty/None choices via
its retry path instead of iterating.
Based on the diagnosis in #56525 by @spiky02plateau (that PR normalized
the MoA aggregator return with a one-shot chunk iterator; the common
text/tool-call crash was already fixed at this seam by #55932, so this
extends the existing guard to cover only the remaining empty/None-choices
gap).
Fixes#55933
* refactor(streaming): simplify empty-choices guard body and parametrize tests
Post-review cleanup (no behavior change):
- Inline the single-use `response_choices` local and drop the redundant
`if first_choice is not None else None` guard (getattr(None, ...) already
returns the default safely).
- Collapse the two near-identical empty/None-choices regression tests into
one `@pytest.mark.parametrize` case.
Mutation-verified: reverting the guard to the old non-empty-list condition
still makes both parametrized cases fail with the historical
'types.SimpleNamespace' object is not iterable.
---------
Co-authored-by: spiky02plateau <155588579+spiky02plateau@users.noreply.github.com>
