Reasoning streaming state now derives only from the live stream phase
(streaming/cooldown), never from missing persisted timing data. A cached
part without time.end is no longer treated as live just because the
timing field is absent, so completed reasoning renders in full on load
instead of replaying a fake stream.
While resolving the merge onto main, also fixed a regression the merge
uncovered: main had added block-level streaming reveal (commitStreamedText)
to ReasoningPart since this fix was authored, which caused the busy
"Thinking…" header to stay hidden for the first moments of a short,
single-paragraph streaming response (no committed line yet). The busy
header now mounts as soon as streaming starts, independent of whether
any text has been committed for display.
Closes#2020
Bohdan Triapitsyn
e64fc710fc