mesh-issues: keep every issue in the log changes and the bucket as its fold, so the record outlives the bucket's cap and a week of events (hq ADR 0300, issues 501, 502)

Every write appends one operation at the issue's last sequence before the
bucket is written; a refused append writes nothing. The start carries what
the bucket holds, refolds what is behind and indexes every issue in memory,
so list answers from memory with a ranked search and a before cursor.

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

@@ -167,7 +167,7 @@ func (t *Tracker) recordFix(pr, state, why string, merged bool, at time.Time, on
 			// the same pull request at most, and an older one is history.
 			continue
 		}
-		if _, err := t.change(n, func(i *Issue) error {
+		if _, err := t.change(n, Act{Op: "delivery", By: Seat}, func(i *Issue) error {
 			f := fixOf(i, pr)
 			if f == nil {
 				i.Fixes = append(i.Fixes, Fix{PullRequest: pr})
@@ -242,7 +242,7 @@ func (t *Tracker) afterFix(n uint64) error {
 					}
 				}
 				claimed := false
-				if _, err := t.change(n, func(i *Issue) error {
+				if _, err := t.change(n, Act{Op: EventReadyToVerify, By: Seat}, func(i *Issue) error {
 					claimed = false
 					if strings.Join(i.VerifyFor, ",") == strings.Join(prs, ",") {
 						return nil
@@ -290,7 +290,7 @@ func (t *Tracker) clearStuck(is *Issue) error {
 	if err := t.Notify(stuckKey(is.Number), "", "", "", "", "the fix of issue "+keyOf(is.Number)+" is delivered or no longer waited for", true); err != nil {
 		return err
 	}
-	_, err := t.change(is.Number, func(i *Issue) error { i.StuckOpen = false; return nil })
+	_, err := t.change(is.Number, Act{Op: "warned", By: Seat}, func(i *Issue) error { i.StuckOpen = false; return nil })
 	return err
 }
 
@@ -514,7 +514,7 @@ func (t *Tracker) Sweep() (int, error) {
 				}
 			}
 			pr := f.PullRequest
-			if _, err := t.change(n, func(i *Issue) error {
+			if _, err := t.change(n, Act{Op: "warned", By: Seat}, func(i *Issue) error {
 				if g := fixOf(i, pr); g != nil {
 					g.StuckSaid = true
 				}