The credential wait's test stays under a second, and a failed watch says the re-read, not a restart (issue 1496)

Review of 3baeaec: TestAwaitCredential took 1.9 s, over the unit limit; it now
sets the watch's settle to 10 ms, writes at 20 ms and gives up at 100 ms (0.2 s).
The watch's journal line for a failure named a bundle and a restart; the
credential wait now says it is read again every 30 s instead.

node-tools/internal/runtime/watch.go

@@ -35,24 +35,31 @@ type bundleWatch struct {
 	changed func()
 	logf    func(string, ...any)
 	done    chan struct{}
+	// what names what is watched, and lost what follows when the watch fails, in the words a journal line carries.
+	what, lost string
 }
 
 // WatchFile hears, as the bundles are heard, the directory of the file at path, or the nearest directory above it that
 // exists, and calls changed once at its start and once after each burst of changes there has settled: a runtime waiting
 // for its broker credential reads it again when the node-engine writes it, never on a clock (issue 1496). It answers its
 // stop.
-func WatchFile(path string, changed func(), logf func(string, ...any)) (func(), error) {
-	return watchBundles([]string{path}, changed, logf)
+func WatchFile(path string, changed func(), logf func(string, ...any), lost string) (func(), error) {
+	return watch([]string{path}, changed, logf, path, lost)
 }
 
 // watchBundles starts the watch of the entrypoints at paths. It answers its stop.
 func watchBundles(paths []string, changed func(), logf func(string, ...any)) (func(), error) {
+	return watch(paths, changed, logf, "the bundles", "a bundle placed or changed there is served only after a restart")
+}
+
+// watch starts the watch of the files at paths, named what in its words; lost says what follows when it fails.
+func watch(paths []string, changed func(), logf func(string, ...any), what, lost string) (func(), error) {
 	fd, err := unix.InotifyInit1(unix.IN_CLOEXEC | unix.IN_NONBLOCK)
 	if err != nil {
 		return nil, fmt.Errorf("inotify: %w", err)
 	}
 	w := &bundleWatch{fd: fd, paths: paths, byWD: map[int]string{}, settle: Settle, changed: changed, logf: logf,
-		done: make(chan struct{})}
+		done: make(chan struct{}), what: what, lost: lost}
 	if err := unix.Pipe2(w.wake[:], unix.O_CLOEXEC|unix.O_NONBLOCK); err != nil {
 		unix.Close(fd)
 		return nil, fmt.Errorf("pipe: %w", err)
@@ -83,7 +90,7 @@ func (w *bundleWatch) arm() {
 			}
 			wd, err := unix.InotifyAddWatch(w.fd, dir, watchMask)
 			if err != nil {
-				w.logf("[mesh-tools] cannot watch %s for %s's bundle: %v; a bundle placed or changed there is served only after a restart", dir, p, err)
+				w.logf("[mesh-tools] cannot watch %s for %s: %v; %s", dir, p, err, w.lost)
 				break
 			}
 			w.byWD[wd] = dir
@@ -126,7 +133,7 @@ func (w *bundleWatch) loop() {
 			continue
 		}
 		if err != nil {
-			w.logf("[mesh-tools] the watch of the bundles stopped: %v; a bundle placed or changed later is served only after a restart", err)
+			w.logf("[mesh-tools] the watch of %s stopped: %v; %s", w.what, err, w.lost)
 			return
 		}
 		if fds[1].Revents != 0 {