mesh-issues: resume an interrupted carry by revision and fault one issue instead of the whole start, so no kept value is lost and the tracker always starts (review of PR 228)

An open's lost answer is judged by the issue's first entry; an entry that does not
fold faults its issue on start; a value written beside the log is never folded over;
one issue is kept in at most 252 KiB so its whole operation fits a log entry.

modules/mesh-issues/cmd/mesh-issues/tracker.go

@@ -10,7 +10,6 @@ import (
 	"sort"
 	"strings"
 	"sync"
-	"sync/atomic"
 	"time"
 
 	stdio "git.novox.be/novox/mesh-sdk/go"
@@ -46,8 +45,6 @@ type Tracker struct {
 	groom    grooming
 	held     *memoryView
 	heldOnce sync.Once
-	// carryDeletes counts the deletions the carry passed over among the values the bucket kept.
-	carryDeletes atomic.Int64
 }
 
 // The events this module says, one per kind of change.