fix(calendar): prefer the destination provider for meeting generation

docs/ARCHITECTURE.md

@@ -449,6 +449,8 @@ committed booking) — which is why the reconciler (§11) exists.
 
 ## 10. Calendar integration (provider abstraction)
 
+The connected-provider lookup prefers the destination connection. A conflict-only connection must not select the provider used when deciding how to generate a meeting link.
+
 Calnode talks to calendars through a **provider abstraction**, not a single vendor:
 
 - **`internal/calendar`** defines the `Provider` interface (Name, InvitesGuests,

internal/calendar/calendar.go

@@ -136,7 +136,7 @@ func (s *Service) providerForDestination(ctx context.Context, userID string) Pro
 func (s *Service) Connected(ctx context.Context, userID string) (bool, string, error) {
 	var name string
 	err := s.db.QueryRowContext(ctx,
-		`SELECT provider FROM calendar_connections WHERE user_id = ? LIMIT 1`, userID).Scan(&name)
+		`SELECT provider FROM calendar_connections WHERE user_id = ? ORDER BY is_destination DESC, created_at ASC LIMIT 1`, userID).Scan(&name)
 	if err == sql.ErrNoRows {
 		return false, "", nil
 	}

internal/calendar/destination_provider_test.go

@@ -0,0 +1,46 @@
+package calendar
+
+import (
+	"context"
+	"testing"
+
+	"github.com/calnode/calnode/internal/db"
+)
+
+func TestConnectedPrefersDestinationOverOlderCalDAV(t *testing.T) {
+	database, err := db.Open("sqlite://:memory:")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer database.Close()
+	if err := db.Migrate(database); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := database.Exec(`INSERT INTO users (id, email, name, iana_timezone, is_admin, created_at)
+		VALUES ('host', 'host@example.com', 'Host', 'Europe/Amsterdam', 0, '2026-09-20T00:00:00Z')`); err != nil {
+		t.Fatal(err)
+	}
+	for _, provider := range []string{"caldav", "google"} {
+		destination := 0
+		if provider == "google" {
+			destination = 1
+		}
+		if _, err := database.Exec(`INSERT INTO calendar_connections
+			(id, user_id, provider, access_token_enc, calendar_id, check_conflicts, is_destination, created_at)
+			VALUES (?, 'host', ?, 'encrypted', 'primary', 1, ?, '2026-09-20T00:00:00Z')`, provider, provider, destination); err != nil {
+			t.Fatal(err)
+		}
+	}
+	svc := NewService(database)
+	connected, provider, err := svc.Connected(context.Background(), "host")
+	if err != nil || !connected || provider != "google" {
+		t.Fatalf("connected=%v provider=%q error=%v; want Google destination", connected, provider, err)
+	}
+	if err := svc.SetDestination(context.Background(), "host", "caldav", ""); err != nil {
+		t.Fatal(err)
+	}
+	_, provider, err = svc.Connected(context.Background(), "host")
+	if err != nil || provider != "caldav" {
+		t.Fatalf("provider=%q error=%v; want changed destination", provider, err)
+	}
+}