Wire wake and identity into crossbar; v2 smoke and README

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

internal/proxy/forward.go

@@ -152,6 +152,30 @@ func (p *Handler) writeError(w http.ResponseWriter, status int, msg string) {
 	_ = json.NewEncoder(w).Encode(map[string]string{"error": msg})
 }
 
+// writeNoHealthyHost answers the 503 when no candidate woke. The body names the
+// hosts that were asked to wake (an empty list, never null), and the row
+// records the miss.
+func (p *Handler) writeNoHealthyHost(w http.ResponseWriter, route, model, fp string, started time.Time, tried []string) {
+	if tried == nil {
+		tried = []string{}
+	}
+	p.writeRecord(store.Request{
+		Route:   route,
+		FP:      fp,
+		Model:   model,
+		Started: started,
+		TotalMs: time.Since(started).Milliseconds(),
+		Status:  http.StatusServiceUnavailable,
+		Err:     "no healthy host",
+	})
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(http.StatusServiceUnavailable)
+	_ = json.NewEncoder(w).Encode(map[string]any{
+		"error": "no healthy host",
+		"woke":  tried,
+	})
+}
+
 // writeRecord writes one accounting row, logging (never returning) a recorder error.
 func (p *Handler) writeRecord(req store.Request) {
 	if p.rec == nil {