Wake: a target may list several broadcast addresses

Config keeps broadcast (one) and adds broadcasts (a list); exactly one must
be present. Wake.Addresses() returns Broadcast then Broadcasts; checkWake
errors on both-set, neither-or-empty, and non-host:port entries. Waker sends
to every address in order, logging/past a failure so one dead address does
not stop the others, and returns false only when none could be sent.

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

internal/config/identity.go

@@ -7,11 +7,24 @@ import (
 )
 
 // Wake is the magic-wake pattern sent to a host to rouse it: its MAC, the
-// broadcast address to aim at, and how long to wait for the answer.
+// broadcast address(s) to aim at, and how long to wait for the answer. A host
+// that roams between networks names several, so Broadcast (one) and Broadcasts
+// (a list) are alternatives: exactly one must be set.
 type Wake struct {
-	MAC       string   `toml:"mac"`
-	Broadcast string   `toml:"broadcast"`
-	Wait      Duration `toml:"wait"`
+	MAC        string   `toml:"mac"`
+	Broadcast  string   `toml:"broadcast"`
+	Broadcasts []string `toml:"broadcasts"`
+	Wait       Duration `toml:"wait"`
+}
+
+// Addresses is Broadcast (when set) followed by Broadcasts: the ordered list to
+// send wake packets to, never empty for a parsed config.
+func (w *Wake) Addresses() []string {
+	addrs := make([]string, 0, 1+len(w.Broadcasts))
+	if w.Broadcast != "" {
+		addrs = append(addrs, w.Broadcast)
+	}
+	return append(addrs, w.Broadcasts...)
 }
 
 const (
@@ -40,8 +53,19 @@ func (c *Config) checkWake() *Error {
 			return &Error{Field: wakeField + ".mac", Msg: "must be a MAC address"}
 		}
 
-		if _, _, err := net.SplitHostPort(w.Broadcast); err != nil || w.Broadcast == "" {
+		broadcastSet := w.Broadcast != ""
+		broadcastsSet := len(w.Broadcasts) > 0
+		switch {
+		case broadcastSet && broadcastsSet:
+			return &Error{Field: wakeField + ".broadcasts", Msg: "choose broadcast or broadcasts, not both"}
+		case !broadcastSet && !broadcastsSet:
 			return &Error{Field: wakeField + ".broadcast", Msg: "must be a non-empty host:port"}
+		default:
+			for _, a := range w.Broadcasts {
+				if _, _, err := net.SplitHostPort(a); err != nil || a == "" {
+					return &Error{Field: wakeField + ".broadcasts", Msg: "must be a non-empty host:port"}
+				}
+			}
 		}
 
 		if w.Wait.Duration == 0 {