Finalize conversation and execution group documentation

execution_group.go

@@ -16,6 +16,12 @@ type ExecutionGroupMember struct {
 }
 
 // ExecutionGroupSummary is a detached snapshot of terminal-only totals.
+// Usage sums known terminal values, with Known as their logical OR and
+// Complete as their logical AND. Coverage describes whether every observed
+// member has a terminal, independently of usage completeness. An empty group
+// has complete coverage and known complete zero usage; a group with members
+// but no terminals has unknown, incomplete usage. Overlapping groups are not
+// generally additive.
 type ExecutionGroupSummary struct {
 	Members                  []ExecutionGroupMember `json:"members"`
 	TerminalCoverageComplete bool                   `json:"terminal_coverage_complete"`