feat: pre-load reply threads from the feed

When a reply is visible in NoteCompose, eagerly subscribe to its thread
root (filter on the root's e/a tag, like the thread screen) so opening the
conversation finds it already loaded. The observer resolves the root and
keys on its id, so sibling replies share one subscription and root notes
are skipped.

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/note/types/Text.kt

@@ -48,6 +48,7 @@ import com.vitorpamplona.amethyst.ui.note.ReplyNoteComposition
 import com.vitorpamplona.amethyst.ui.note.elements.DisplayUncitedHashtags
 import com.vitorpamplona.amethyst.ui.note.nip22Comments.DisplayExternalId
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
+import com.vitorpamplona.amethyst.ui.screen.loggedIn.threadview.datasources.PreloadThreadForReply
 import com.vitorpamplona.amethyst.ui.theme.HalfVertSpacer
 import com.vitorpamplona.amethyst.ui.theme.StdVertSpacer
 import com.vitorpamplona.amethyst.ui.theme.placeholderText
@@ -82,6 +83,10 @@ fun RenderTextEvent(
     val noteEvent = note.event ?: return
 
     if (unPackReply != ReplyRenderType.NONE) {
+        // Eagerly pull the rest of this reply's thread while it's on screen, so opening
+        // the conversation finds it already loaded. No-op when the note is a root itself.
+        PreloadThreadForReply(note, accountViewModel)
+
         val canShowReply by
             remember(note) {
                 derivedStateOf {

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/threadview/datasources/ThreadFilterAssemblerSubscription.kt

@@ -22,8 +22,11 @@ package com.vitorpamplona.amethyst.ui.screen.loggedIn.threadview.datasources
 
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.remember
+import com.vitorpamplona.amethyst.commons.model.ThreadAssembler
 import com.vitorpamplona.amethyst.commons.relayClient.subscriptions.LifecycleAwareKeyDataSourceSubscription
 import com.vitorpamplona.amethyst.model.Account
+import com.vitorpamplona.amethyst.model.LocalCache
+import com.vitorpamplona.amethyst.model.Note
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
 
@@ -52,3 +55,29 @@ fun ThreadFilterAssemblerSubscription(
 
     LifecycleAwareKeyDataSourceSubscription(state, filterAssembler)
 }
+
+/**
+ * Eagerly pre-loads the whole thread of a reply that is visible in a feed.
+ *
+ * When a reply shows up in `NoteCompose`, this resolves the thread root and opens
+ * the same root subscription the thread screen uses (a filter on the root's `e`/`a`
+ * tag, covering NIP-10 and NIP-22 event/addressable roots), so tapping into the
+ * conversation finds it already loaded. Keying on the resolved root id means every
+ * visible reply that shares a root collapses onto a single subscription, and a note
+ * that is itself a root (no parent) is skipped — nothing to pre-load.
+ */
+@Composable
+fun PreloadThreadForReply(
+    note: Note,
+    accountViewModel: AccountViewModel,
+) {
+    val rootId =
+        remember(note) {
+            val root = ThreadAssembler(LocalCache).findRoot(note.idHex)
+            if (root != null && root != note) root.idHex else null
+        }
+
+    if (rootId != null) {
+        ThreadFilterAssemblerSubscription(rootId, accountViewModel)
+    }
+}