Make delivery and integration failures explicit

Persist reminder presentations and retry state, atomically complete collapsed deliveries, fall back across away reaches, and block permanent failures visibly (V-715, V-678). Fail closed when enabled integrations lack credentials and keep remote arms explicitly dark (V-691). Give mavweb one sanitized, request-correlated error contract (V-689). Owner explicitly requested direct commits to master.

cmd/mavweb/notifications.go

@@ -2,7 +2,7 @@ package main
 
 import (
 	_ "embed"
-	"log"
+	"fmt"
 	"net/http"
 	"strconv"
 
@@ -48,14 +48,14 @@ func deliveryRows(as []ipc.DeliveryAttempt) []deliveryRow {
 }
 
 func handleNotifications(w http.ResponseWriter, r *http.Request, core ipc.CoreAPI) {
-	if !requireCore(w, core, "notifications") {
+	if !requireCore(w, r, core, "notifications") {
 		return
 	}
 	ctx := r.Context()
 	nudges, err := core.RecentNudges(ctx, 50)
 	if err != nil {
-		log.Printf("notifications: %v", err)
-		http.Error(w, "notifications error: "+err.Error(), http.StatusBadGateway)
+		writeProblem(w, r, http.StatusBadGateway, problemCoreReadFailed,
+			"notifications unavailable", fmt.Errorf("read recent nudges: %w", err))
 		return
 	}
 	// The outbox, on the page that already answers "what did she send".
@@ -66,7 +66,8 @@ func handleNotifications(w http.ResponseWriter, r *http.Request, core ipc.CoreAP
 	if err != nil {
 		// The nudge list is still worth showing, so this is a note on the page
 		// rather than a dead page.
-		log.Printf("notifications: delivery attempts: %v", err)
+		logProblem(r, http.StatusOK, problemCoreReadFailed,
+			"delivery attempts unavailable", fmt.Errorf("read delivery attempts: %w", err))
 	}
 	renderPage(w, notificationsTmpl, map[string]any{
 		"Nudges":   nudges,