Answer the review of hq issues 348 and 349: gaps, parts, the newest merge in any state

- A reopened fault keeps its gaps: it was there at a send unless the send
  fell in one, so a send that breaks a machine recovered before it still
  fails its gate (A2).
- An undecided part holds only the conditions that name it (A4).
- D2 holds a silent resolver for the next run again, refused or not: a
  burst of refusals is also a restart (A3).
- A late merge is planned at the newest planned merge of its branch in any
  state, not only an open one (A1); merge times to the nanosecond (A5).

cmd/mesh-controller/gate.go

@@ -209,8 +209,9 @@ func judgeHealth(module, component string, m catalogue.Manifest, machine string,
 		return healthNotYet, fmt.Sprintf("%s reported %q", machine, r.Outcome)
 	}
 	// **No new condition about it**: about the machine itself, or naming the module on that machine,
-	// raised since the judging began. The gate's own are not evidence about the build. A fault reopened
-	// since, that began before the send, is not new (Began, novox/hq issue 348).
+	// raised since the judging began. The gate's own are not evidence about the build. A fault that was
+	// there at the send and reopened since is not new; one that had cleared before the send and came back
+	// after it is (OpenAt, novox/hq issue 348).
 	if f.judged {
 		if f.openErr != nil {
 			return healthNotYet, "what is wrong cannot be read, so whether the build made anything wrong is not known: " +
@@ -220,7 +221,7 @@ func judgeHealth(module, component string, m catalogue.Manifest, machine string,
 			// A wait for a person's new login, or for a directory used as found to be handed over, is the module's
 			// reading, not a fault raised since the send: the gate reads it from the statement below (ADR 0254,
 			// novox/hq issue 339).
-			if c.Source == gateProbe || c.Began().Before(since) || c.Kind == kindReloginNeeded || c.Kind == kindUsedAsFound {
+			if c.Source == gateProbe || c.OpenAt(since) || c.Kind == kindReloginNeeded || c.Kind == kindUsedAsFound {
 				continue
 			}
 			onIt := c.Subject.Machine == machine || slices.Contains(c.Subject.Also, machine) ||
@@ -332,7 +333,7 @@ func aboutTheMachine(machine string, moved []string, since time.Time, f gateFact
 		aboutIt := c.Subject.Scope == conditions.ScopeMachine && (c.Subject.ID == machine || c.Subject.Machine == machine ||
 			slices.Contains(c.Subject.Also, machine))
 		// A directory used as found waits for a person, whatever the send did (novox/hq issue 339).
-		if !aboutIt || c.Source == gateProbe || c.Began().Before(since) || c.Kind == kindUsedAsFound {
+		if !aboutIt || c.Source == gateProbe || c.OpenAt(since) || c.Kind == kindUsedAsFound {
 			kept = append(kept, c)
 			continue
 		}