Session-sized task

A unit of work small enough for one agent session to finish: one to five files, clear acceptance criteria, one commit.

Anything touching more than about five files across domains, or carrying several independent outcomes, gets split. Anything with no testable outcome gets merged into its neighbour.

The size exists so that parallelism can be reasoned about honestly. Every claim that two tasks can run at once is checked against which files each one writes, rather than asserted.