mesh-issues and mesh-knowledge: milestones are records of the issue tracker, and progress reads them (ADR 0493 §1 to §4, issue 1781)

mesh-issues keeps each design's milestone in the state milestones (history 5), says milestone-set and
milestone-moved, and serves milestones, milestone-set and milestone-move. An issue's milestone is its own link
of kind milestone, so at most one milestone per issue is checked inside the issue's own write; kind commit
links a fixing commit. The triage links no milestone, pull request or commit. import with milestones=N seeds
a design's table once. mesh-knowledge's progress reads issue-tracker.milestones and its table parse is gone.

Squashed from four commits so the branch history does not carry a compiled bundle that was committed by
mistake (6 MB); the path is now in .gitignore.

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

@@ -215,10 +215,18 @@ const (
 	LinkDesign      = "design"
 	LinkCondition   = "condition"
 	LinkDelivery    = "delivery"
+	// LinkMilestone is the one milestone an issue belongs to, design/id (ADR 0493 §1, §2).
+	LinkMilestone = "milestone"
+	// LinkCommit is a commit that fixes the issue, repository@full sha (ADR 0493 §4).
+	LinkCommit = "commit"
 )
 
 // LinkKinds is every kind, in the order they are told.
-var LinkKinds = []string{LinkDuplicates, LinkRelatesTo, LinkDependsOn, LinkPullRequest, LinkDecision, LinkDesign, LinkCondition, LinkDelivery}
+var LinkKinds = []string{LinkDuplicates, LinkRelatesTo, LinkDependsOn, LinkPullRequest, LinkDecision, LinkDesign, LinkCondition, LinkDelivery,
+	LinkMilestone, LinkCommit}
+
+// madeByPeople are the kinds only a person or a session links, never the triage (ADR 0493 §4).
+var madeByPeople = []string{LinkPullRequest, LinkMilestone, LinkCommit}
 
 var (
 	pullRequest = regexp.MustCompile(`^[a-z0-9][a-z0-9._-]{0,99}#[1-9][0-9]{0,6}$`)
@@ -280,6 +288,15 @@ func checkTarget(kind, target string) (string, error) {
 	case LinkDelivery:
 		ok, shape = deliveryID.MatchString(t), "a delivery's id as mesh-delivery names it: the repository as owner/name, @ and twelve "+
 			"characters of its commit, such as novox/mesh-controller@d2e9dc61590f"
+	case LinkMilestone:
+		var c string
+		c, ok = checkMilestoneTarget(t)
+		if ok {
+			t = c
+		}
+		shape = "a milestone as design/id, such as 47/R6"
+	case LinkCommit:
+		ok, shape = commitRef.MatchString(t), "a repository, @ and the commit's full 40-character id, such as mesh-catalog@"+strings.Repeat("0", 40)
 	default:
 		return "", fmt.Errorf("kind %q is not a kind of link: one of %s", kind, strings.Join(LinkKinds, ", "))
 	}