Finds the most recent captured body text at or before stepIndex.
Bodies are only captured (as text) when they change; unchanged bodies
are marked unchanged: true with no text, so this walks backwards
through step snapshots while a body stays unchanged with no text,
stopping at the first text found, at trace.initial, or at a step
whose body changed but wasn't captured as text (binary/too large) — in
which case there is nothing valid to backfill from and the result is
null.
Finds the most recent captured body text at or before
stepIndex.Bodies are only captured (as
text) when they change; unchanged bodies are markedunchanged: truewith notext, so this walks backwards through step snapshots while a body staysunchangedwith notext, stopping at the firsttextfound, attrace.initial, or at a step whose body changed but wasn't captured as text (binary/too large) — in which case there is nothing valid to backfill from and the result isnull.