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/mavend/ntfy_wiring_test.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/kami/maven/internal/delivery/ntfysink"
+)
+
+func TestWireNtfySinkRejectsMissingCredentialWhenEnabled(t *testing.T) {
+	_, err := wireNtfySink(&ntfysink.Config{
+		BaseURL: "https://ntfy.example", Topic: "maven",
+	})
+	if err == nil {
+		t.Fatal("expanded-empty credential did not fail an enabled reach")
+	}
+}
+
+func TestWireNtfySinkLeavesExplicitlyDisabledReachDark(t *testing.T) {
+	sink, err := wireNtfySink(&ntfysink.Config{
+		Disabled: true, BaseURL: "https://ntfy.example", Topic: "maven",
+	})
+	if err != nil {
+		t.Fatalf("wireNtfySink: %v", err)
+	}
+	if sink != nil {
+		t.Fatal("disabled reach built a live sink")
+	}
+}
+
+func TestWireNtfySinkRejectsMalformedEnabledConfig(t *testing.T) {
+	_, err := wireNtfySink(&ntfysink.Config{Token: "token", Topic: "maven"})
+	if err == nil {
+		t.Fatal("malformed enabled config did not fail wiring")
+	}
+}