The check for whether the block tree db has been wiped before calling
NeedsRedownload() is confusing. The boolean is set in case of a reindex.
It was originally introduced to guard NeedsRedownload in case of a
reindex in #21009. However NeedsRedownload already returns early if the
chain's tip is not loaded. Since that is the case during a reindex, the
pre-check is redundant.
The src/node/ directory contains code that needs to access node state
(state in CChain, CBlockIndex, CCoinsView, CTxMemPool, and similar
classes).
Code in src/node/ is meant to be segregated from code in
src/wallet/ and src/qt/, to ensure wallet and GUI
code changes don't interfere with node operation, to allow wallet and GUI code
to run in separate processes, and to perhaps eventually allow wallet and GUI
code to be maintained in separate source repositories.
As a rule of thumb, code in one of the src/node/,
src/wallet/, or src/qt/ directories should avoid
calling code in the other directories directly, and only invoke it indirectly
through the more limited src/interfaces/ classes.
This directory is at the moment
sparsely populated. Eventually more substantial files like
src/validation.cpp and
src/txmempool.cpp might be moved there.