This change drops the last kernel dependency on shutdown.cpp. It also adds new hooks for libbitcoinkernel applications to be able to interrupt kernel operations when the chain tip changes. This is a refactoring that does not affect behavior. (Looking at the code it can appear like the new break statement in the ActivateBestChain function is a change in behavior, but actually the previous StartShutdown call was indirectly triggering a break before, because it was causing m_chainman.m_interrupt to be true. The new code just makes the break more obvious.)
src/node/
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.