The WT_BTREE handle keeps its flags in a single non-atomic uint32_t field, manipulated with the F_SET/F_CLR/F_ISSET macros. These perform non-atomic read-modify-write, so a flag update that races with a concurrent update to a different flag on the same handle can lose one of the writes.

WT_BTREE_IN_MEMORY has been moved to a new atomic flags field (flags_atomic) and is now accessed with the atomic flag macros, because it is cleared at runtime while other threads may be reading or writing the flags. This ticket tracks a broader audit of the remaining WT_BTREE flags to determine which are modified after the handle is in use by multiple threads, and to move those to atomic access as well.

Deliverables:

• Classify each WT_BTREE flag as set-once-at-open versus mutated concurrently.
• Move concurrently mutated flags to flags_atomic and convert their call sites to the atomic macros.
• Document the invariant for the flags that remain in the non-atomic field.