getThread ordered purely by created_at, which is second-granular on MySQL
and SQLite. A user turn and the assistant reply routinely land in the same
second, so their relative order was whatever the storage engine returned.
The client rebuilds the conversation tree from parent_id, so a child ahead
of its parent corrupts the thread.
Adds an id tiebreaker for a deterministic database order, then a stable
topological pass that guarantees parents precede children while preserving
sibling order. Dangling parent references are treated as roots and cycles
are appended, so no message is ever dropped.
Thomas Camlong
ajnart