Expose Offline Region ID property on MLNOfflinePack for Darwin/iOS (#4161)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

platform/darwin/src/MLNOfflinePack.h

@@ -121,6 +121,18 @@ typedef struct __attribute__((objc_boxable)) MLNOfflinePackProgress {
 MLN_EXPORT
 @interface MLNOfflinePack : NSObject
 
+/**
+ The unique identifier of the offline region associated with this pack.
+
+ This identifier is an auto-incrementing value assigned by the offline database
+ when the region is created. It is stable across application launches and can be
+ used to distinguish between different offline packs.
+
+ The value is `nil` for packs that have not yet been saved to the database. In
+ Swift, this property is typed as `NSNumber?`.
+ */
+@property (nonatomic, readonly, nullable) NSNumber *regionId;
+
 /**
  The region for which the pack manages resources.
  */

platform/darwin/src/MLNOfflinePack.mm

@@ -92,6 +92,14 @@ private:
             @"MLNOfflinePack was not invalided prior to deallocation.");
 }
 
+- (nullable NSNumber *)regionId {
+  if (_state == MLNOfflinePackStateInvalid || !_mbglOfflineRegion) {
+    return nil;
+  }
+
+  return @(_mbglOfflineRegion->getID());
+}
+
 - (id<MLNOfflineRegion>)region {
   MLNAssertOfflinePackIsValid();
 

platform/darwin/test/MLNOfflinePackTests.mm

@@ -16,6 +16,7 @@
       invalidPack.state, MLNOfflinePackStateInvalid,
       @"Offline pack should be invalid when initialized independently of MLNOfflineStorage.");
 
+  XCTAssertNil(invalidPack.regionId, @"Invalid offline pack should return nil regionID.");
   XCTAssertThrowsSpecificNamed(
       invalidPack.region, NSException, MLNInvalidOfflinePackException,
       @"Invalid offline pack should raise an exception when accessing its region.");

platform/darwin/test/MLNOfflineStorageTests.mm

@@ -752,6 +752,14 @@
                    XCTAssertEqual([MLNOfflineStorage sharedOfflineStorage].packs.count,
                                   countOfPacks + 1,
                                   @"Adding contents of sideload_sat.db should add one pack.");
+                   MLNOfflinePack *lastPack =
+                       [MLNOfflineStorage sharedOfflineStorage].packs.lastObject;
+                   XCTAssertNotNil(lastPack, @"Pack should exist after adding contents.");
+                   XCTAssertNotNil(lastPack.regionId,
+                                   @"Region ID should not be nil after a pack is added.");
+                   XCTAssertGreaterThan(
+                       lastPack.regionId.longLongValue, 0,
+                       @"Region ID should be greater than 0 after a pack is added.");
                  }];
 
   // Invalid database type