add missing file (#392)

app/src/main/java/com/bitchat/android/nostr/GeohashConversationRegistry.kt

@@ -0,0 +1,22 @@
+package com.bitchat.android.nostr
+
+import java.util.concurrent.ConcurrentHashMap
+
+/**
+ * GeohashConversationRegistry
+ * - Global, thread-safe registry of conversationKey (e.g., "nostr_<pub16>") -> source geohash
+ * - Enables routing geohash DMs from anywhere by providing the correct geohash identity
+ */
+object GeohashConversationRegistry {
+    private val map = ConcurrentHashMap<String, String>()
+
+    fun set(convKey: String, geohash: String) {
+        if (geohash.isNotEmpty()) map[convKey] = geohash
+    }
+
+    fun get(convKey: String): String? = map[convKey]
+
+    fun snapshot(): Map<String, String> = map.toMap()
+
+    fun clear() = map.clear()
+}