Leave an eligible index for a confirmed collect instead of letting it go alone

Let go of alone after a build, an index's platforms stayed for ever under a record that
said collected, so no later collect could reach them (re-review of #144).

internal/catalogue/verbs.go

@@ -451,7 +451,8 @@ var ControllerVerbs = []Verb{
 		"listed, nothing held or deleted. With confirm and why: every kept archive held first, then each eligible " +
 		"artifact let go of, oldest first, and recorded collected — a hand act, recorded with its why. A confirmed " +
 		"collect lets an index go with the platform manifests no kept index names (read first; any read that " +
-		"fails lets nothing go); the sweep after a build lets an index go alone (novox/hq ADR 0257). Bounded by " +
+		"fails lets nothing go); the sweep after a build leaves an eligible index for such a collect (novox/hq ADR " +
+		"0257). Bounded by " +
 		"most (500 by default, at most 5000) and 45 seconds; what is left is said. Bytes are reclaimed by the " +
 		"store's nightly collector. Never touches a digest the mesh did not record (novox/hq ADR 0189, ADR 0251).",
 		Input: schema(map[string]string{