Measure each fix from the move to fixing to delivered, and say one over its budget (issue 403)

hq ADR 0313: the operator's five minutes start when an agent moves the issue
to fixing, not at the merge. mesh-delivery says on each transition, and in
checks, when the pull request opened, when it merged and the class of what it
moves. mesh-issues keeps the first move to fixing, the fix time with its four
phases once the last fix is delivered, serves fix-times, and says
issue-tracker.fix.<class>.over-budget on the operator's channel, cleared by the
next fix of that class within budget.

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

@@ -36,8 +36,12 @@ type Tracker struct {
 	Judge Judgement
 	// Deliveries answers a pull request's delivery (ADR 0279 §3, ADR 0281); nil asks nothing.
 	Deliveries DeliveryState
-	// Notify tells the operator's channel of a stuck fix (ADR 0281); nil says nothing there.
+	// Notify tells the operator's channel of a stuck fix (ADR 0281) and of a fix over its budget (ADR 0313); nil
+	// says nothing there.
 	Notify Notifier
+	// Approval answers when a pull request was first approved at its head (ADR 0313 §4); nil asks nothing, and a
+	// fix's review is counted with its checks.
+	Approval Approval
 	// CallerOf is who called, for the arguments one call was handed (stdio.CallerOf); nil proves nobody.
 	CallerOf func(map[string]any) string
 	// Log is the tracker's record, the log `changes` (novox/hq ADR 0300); the bucket `issues` is its fold.
@@ -456,6 +460,11 @@ func (t *Tracker) move(by string, a MoveAsk) (*Moved, error) {
 			return err
 		}
 		is.Status = to
+		if to == StatusFixing && from != StatusFixing && is.FixingFrom == nil {
+			// The first move to fixing starts the fix time; none after it restarts it (ADR 0313 §1).
+			start := at
+			is.FixingFrom = &start
+		}
 		if (to == StatusResolved || to == StatusWontfix) && from != to {
 			is.Closed = &at
 		} else if to != StatusResolved && to != StatusWontfix {