fix(push-demo): preserve thread root for temporary replies

Signed-off-by: Tom Brow <tomb@block.xyz>
Co-authored-by: Codex <noreply@openai.com>
Ai-assisted: true

mobile/ios/BuzzPushKit/Sources/BuzzPushKit/BuzzPushNotificationResolver.swift

@@ -456,10 +456,7 @@ public final class BuzzPushNotificationResolver: BuzzPushNotificationResolving {
     let conversation = channel.flatMap {
       communicationConversation(event: event, community: community, channel: $0)
     }
-    let rootEventID =
-      event.tags.first {
-        $0.count >= 4 && $0[0] == "e" && $0[3] == "root" && !$0[1].isEmpty
-      }?[1] ?? event.id
+    let rootEventID = replyRootEventID(for: event)
     let replyKind = [45_001, 45_003].contains(event.kind) ? 45_003 : 9
     return BuzzPushResolution(
       title: profile?.displayName ?? shortPubkey(event.pubkey),
@@ -491,6 +488,21 @@ public final class BuzzPushNotificationResolver: BuzzPushNotificationResolving {
     )
   }
 
+  /// Resolves the NIP-10 root carried by an incoming message. A direct reply
+  /// to a root commonly carries only a `reply` marker, so that parent is also
+  /// the thread root. Nested replies carry an explicit `root` marker, which
+  /// remains authoritative.
+  private static func replyRootEventID(for event: VerifiedNostrEvent) -> String {
+    for marker in ["root", "reply"] {
+      if let value = event.tags.first(where: {
+        $0.count >= 4 && $0[0] == "e" && $0[3] == marker && !$0[1].isEmpty
+      })?[1] {
+        return value
+      }
+    }
+    return event.id
+  }
+
   private static func ephemeralProfile(
     event: VerifiedNostrEvent,
     communityID: String,

mobile/ios/BuzzPushKit/Tests/BuzzPushKitTests/BuzzPushNotificationResolverTests.swift

@@ -129,6 +129,43 @@ final class BuzzPushNotificationResolverTests: XCTestCase {
     XCTAssertEqual(result?.0.body, "lower ID")
   }
 
+  func testReplyContextUsesReplyMarkerAsRootForDirectReply() throws {
+    let incoming = event(
+      id: "incoming-reply",
+      content: "Reply to the thread root",
+      tags: [
+        ["h", Self.channelID],
+        ["e", "thread-root", "", "reply"],
+      ]
+    )
+
+    let result = BuzzPushNotificationResolver.decodeResolution(
+      events: [incoming],
+      community: community()
+    )
+
+    XCTAssertEqual(try XCTUnwrap(result?.0.replyContext).rootEventID, "thread-root")
+  }
+
+  func testReplyContextPrefersExplicitRootForNestedReply() throws {
+    let incoming = event(
+      id: "incoming-nested-reply",
+      content: "Nested reply",
+      tags: [
+        ["h", Self.channelID],
+        ["e", "thread-root", "", "root"],
+        ["e", "immediate-parent", "", "reply"],
+      ]
+    )
+
+    let result = BuzzPushNotificationResolver.decodeResolution(
+      events: [incoming],
+      community: community()
+    )
+
+    XCTAssertEqual(try XCTUnwrap(result?.0.replyContext).rootEventID, "thread-root")
+  }
+
   func testResolveSucceedsAndMutatesGatewayContent() throws {
     let event = try JSONDecoder().decode(
       VerifiedNostrEvent.self,