Bits and pieces about how this came to be...
Here are some discussions which look like the first ones to mention this concept.
The first bug
Is number 4 on the Apache Bugzilla system.
Cocoon digital archeology
Some mail datamining by Stefanomazzocchi.
Flow - the vision
The Cocoon Wiki is born
The Original Scheme Implementation of Flow
...there's plenty of space here to add more interesting/anecdotical stuff, please do!