feat(budget): bidirectional sync between reservations and budget items

- Link budget items to reservations via reservation_id column
- Update budget entry when reservation price changes (not create duplicate)
- Delete budget entry when reservation price is cleared
- Sync price back to reservation when edited in budget panel
- Lock budget item name when linked to a reservation
- Add migration 73 for reservation_id on budget_items

server/src/db/migrations.ts

@@ -822,6 +822,10 @@ function runMigrations(db: Database.Database): void {
     () => {
       db.exec('DROP TABLE IF EXISTS notification_preferences;');
     },
+    // Migration 73: Add reservation_id to budget_items for linking budget entries to reservations
+    () => {
+      try { db.exec('ALTER TABLE budget_items ADD COLUMN reservation_id INTEGER REFERENCES reservations(id) ON DELETE SET NULL DEFAULT NULL'); } catch (err: any) { if (!err.message?.includes('duplicate column name')) throw err; }
+    },
   ];
 
   if (currentVersion < migrations.length) {

server/src/routes/budget.ts

@@ -3,6 +3,7 @@ import { authenticate } from '../middleware/auth';
 import { broadcast } from '../websocket';
 import { checkPermission } from '../services/permissions';
 import { AuthRequest } from '../types';
+import { db } from '../db/database';
 import {
   verifyTripAccess,
   listBudgetItems,
@@ -68,6 +69,22 @@ router.put('/:id', authenticate, (req: Request, res: Response) => {
   const updated = updateBudgetItem(id, tripId, req.body);
   if (!updated) return res.status(404).json({ error: 'Budget item not found' });
 
+  // Sync price back to linked reservation
+  if (updated.reservation_id && req.body.total_price !== undefined) {
+    try {
+      const reservation = db.prepare('SELECT id, metadata FROM reservations WHERE id = ? AND trip_id = ?').get(updated.reservation_id, tripId) as { id: number; metadata: string | null } | undefined;
+      if (reservation) {
+        const meta = reservation.metadata ? JSON.parse(reservation.metadata) : {};
+        meta.price = String(updated.total_price);
+        db.prepare('UPDATE reservations SET metadata = ? WHERE id = ?').run(JSON.stringify(meta), reservation.id);
+        const updatedRes = db.prepare('SELECT * FROM reservations WHERE id = ?').get(reservation.id);
+        broadcast(tripId, 'reservation:updated', { reservation: updatedRes }, req.headers['x-socket-id'] as string);
+      }
+    } catch (err) {
+      console.error('[budget] Failed to sync price to reservation:', err);
+    }
+  }
+
   res.json({ item: updated });
   broadcast(tripId, 'budget:updated', { item: updated }, req.headers['x-socket-id'] as string);
 });

server/src/routes/reservations.ts

@@ -59,6 +59,8 @@ router.post('/', authenticate, (req: Request, res: Response) => {
         category: create_budget_entry.category || type || 'Other',
         total_price: create_budget_entry.total_price,
       });
+      db.prepare('UPDATE budget_items SET reservation_id = ? WHERE id = ?').run(reservation.id, budgetItem.id);
+      budgetItem.reservation_id = reservation.id;
       broadcast(tripId, 'budget:created', { item: budgetItem }, req.headers['x-socket-id'] as string);
     } catch (err) {
       console.error('[reservations] Failed to create budget entry:', err);
@@ -119,18 +121,41 @@ router.put('/:id', authenticate, (req: Request, res: Response) => {
     broadcast(tripId, 'accommodation:updated', {}, req.headers['x-socket-id'] as string);
   }
 
-  // Auto-create budget entry if price was provided
+  // Remove linked budget entry if price was cleared
+  if (!create_budget_entry || !create_budget_entry.total_price) {
+    const linked = db.prepare('SELECT id FROM budget_items WHERE trip_id = ? AND reservation_id = ?').get(tripId, id) as { id: number } | undefined;
+    if (linked) {
+      const { deleteBudgetItem } = require('../services/budgetService');
+      deleteBudgetItem(linked.id, tripId);
+      broadcast(tripId, 'budget:deleted', { id: linked.id }, req.headers['x-socket-id'] as string);
+    }
+  }
+
+  // Auto-create or update budget entry if price was provided
   if (create_budget_entry && create_budget_entry.total_price > 0) {
     try {
-      const { createBudgetItem } = require('../services/budgetService');
-      const budgetItem = createBudgetItem(tripId, {
-        name: title || current.title,
-        category: create_budget_entry.category || type || current.type || 'Other',
-        total_price: create_budget_entry.total_price,
-      });
-      broadcast(tripId, 'budget:created', { item: budgetItem }, req.headers['x-socket-id'] as string);
+      const { createBudgetItem, updateBudgetItem } = require('../services/budgetService');
+      const itemName = title || current.title;
+      const existing = db.prepare('SELECT id FROM budget_items WHERE trip_id = ? AND reservation_id = ?').get(tripId, id) as { id: number } | undefined;
+      if (existing) {
+        const updated = updateBudgetItem(existing.id, tripId, {
+          name: itemName,
+          category: create_budget_entry.category || type || current.type || 'Other',
+          total_price: create_budget_entry.total_price,
+        });
+        broadcast(tripId, 'budget:updated', { item: updated }, req.headers['x-socket-id'] as string);
+      } else {
+        const budgetItem = createBudgetItem(tripId, {
+          name: itemName,
+          category: create_budget_entry.category || type || current.type || 'Other',
+          total_price: create_budget_entry.total_price,
+        });
+        db.prepare('UPDATE budget_items SET reservation_id = ? WHERE id = ?').run(id, budgetItem.id);
+        budgetItem.reservation_id = Number(id);
+        broadcast(tripId, 'budget:created', { item: budgetItem }, req.headers['x-socket-id'] as string);
+      }
     } catch (err) {
-      console.error('[reservations] Failed to create budget entry:', err);
+      console.error('[reservations] Failed to create/update budget entry:', err);
     }
   }