feat(messaging): conflict check before booking appointment

Check for duplicate patient+doctor+date and max 3 slots per time before
creating the appointment. Returns actionable message if conflict found.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/messaging/messaging.service.ts

@@ -344,6 +344,32 @@ ${callerContext ? `\n${callerContext}` : ''}`;
                         const cleanPhone = phoneNumber.replace(/[^0-9]/g, '').slice(-10);
                         const resolved = await callerService.resolve(cleanPhone, auth).catch(() => null);
 
+                        // Conflict check: same doctor + same date
+                        const bookingDate = scheduledAt.split('T')[0];
+                        const existingAppts = await platform.query<any>(
+                            `{ appointments(first: 50, filter: { doctorName: { eq: "${doctorName}" } }, orderBy: [{ scheduledAt: AscNullsLast }]) { edges { node { id scheduledAt status patientName } } } }`,
+                        ).catch(() => ({ appointments: { edges: [] } }));
+
+                        const conflicts = existingAppts.appointments.edges
+                            .map((e: any) => e.node)
+                            .filter((a: any) => a.status === 'SCHEDULED' && a.scheduledAt?.startsWith(bookingDate));
+
+                        // Check if this patient already has a booking with this doctor on the same date
+                        const patientConflict = conflicts.find((a: any) =>
+                            a.patientName?.toLowerCase().includes(patientName.split(' ')[0].toLowerCase()),
+                        );
+                        if (patientConflict) {
+                            logger.log(`[WA-BOOK] Conflict: patient already booked with ${doctorName} on ${bookingDate}`);
+                            return { booked: false, message: `You already have an appointment with ${doctorName} on ${bookingDate}. Would you like to choose a different date?` };
+                        }
+
+                        // Check if the doctor has too many appointments at this exact time
+                        const slotConflicts = conflicts.filter((a: any) => a.scheduledAt === scheduledAt);
+                        if (slotConflicts.length >= 3) {
+                            logger.log(`[WA-BOOK] Conflict: ${doctorName} fully booked at ${scheduledAt} (${slotConflicts.length} existing)`);
+                            return { booked: false, message: `${doctorName} is fully booked at this time. Please choose a different slot.` };
+                        }
+
                         if (resolved?.isNew) {
                             const firstName = patientName.split(' ')[0];
                             const lastName = patientName.split(' ').slice(1).join(' ') || '';