feat(chat): pin messages in DMs and groups

apps/flipcash/core/src/androidMain/res/values/strings.xml

@@ -1832,6 +1832,21 @@
     <string name="title_shareProfileToChats">Share Profile</string>
     <string name="title_shareMessageToChats">Share Message</string>
     <string name="action_forwardMessage">Forward</string>
+    <string name="action_pinMessage">Pin</string>
+    <string name="action_unpinMessage">Unpin</string>
+    <string name="action_jumpToMessage">Jump to message</string>
+    <string name="title_pinnedMessage">Pinned message</string>
+    <string name="cd_pinnedMessageFrom">Pinned message from %1$s: %2$s</string>
+    <string name="label_pinnedEncryptedMessage">Encrypted message</string>
+    <string name="title_pinnedMessages">Pinned Messages</string>
+    <string name="label_pinnedBy">Pinned by %1$s · %2$s</string>
+    <string name="label_pinnedByYou">you</string>
+    <string name="label_pinsFull">Pinned messages are full. Unpin one to pin \"%1$s\"</string>
+    <string name="label_pinsFullUntitled">Pinned messages are full. Unpin one to pin this message</string>
+    <string name="title_pinNotAdded">Couldn\'t pin message</string>
+    <string name="title_unpinFailed">Couldn\'t unpin message</string>
+    <string name="title_messageUnreachable">Couldn\'t find that message</string>
+    <string name="cd_openPinnedMessages">Pinned messages</string>
     <!-- Who the share sheet is for: display name, then @handle -->
     <string name="action_showProfileCard">Show Profile Card</string>
     <string name="action_copyLink">Copy Link</string>

apps/flipcash/core/src/commonMain/kotlin/com/flipcash/app/core/chat/ChatStep.kt

@@ -42,6 +42,11 @@ enum class InviteLinkAction : Parcelable { Share, Revoke }
 @Serializable
 data class NewInviteLinkChoice(val expiry: String, val uses: String) : Parcelable
 
+/** The pinned message tapped in [ChatStep.PinnedMessages]: the chat jumps to it once the list closes. */
+@Parcelize
+@Serializable
+data class PinnedMessageJump(val messageId: Long) : Parcelable
+
 /** A custom paid-reaction amount, in whole US cents. */
 @Parcelize
 @Serializable
@@ -357,6 +362,21 @@ sealed interface ChatStep : FlowStep, Parcelable {
     @Parcelize
     @Serializable
     data class Reactors(val chatId: ChatId, val messageId: Long) : ChatStep, Sheet, HalfSheet
+
+    /**
+     * The chat's pinned messages, newest first (L1). The pins are the conversation's, read when the
+     * chat opened; the route names the chat only. [pinAfterUnpin] is set when it opened because the
+     * chat is at its pin cap (L1b): that message is pinned once an unpin frees a slot.
+     *
+     * Returns the tapped row as a [PinnedMessageJump]; the conversation jumps to it.
+     */
+    @Parcelize
+    @Serializable
+    data class PinnedMessages(val chatId: ChatId, val pinAfterUnpin: Long? = null) :
+        ChatStep,
+        NavigationRetVal<PinnedMessageJump>,
+        Sheet,
+        HalfSheet
 }
 
 /** What opened a [ChatStep.Profile], which decides the actions it offers. */

apps/flipcash/features/messenger/src/main/kotlin/com/flipcash/app/messenger/ChatFlowScreen.kt

@@ -13,6 +13,7 @@ import androidx.compose.runtime.DisposableEffect
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.produceState
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.saveable.rememberSaveable
 import androidx.compose.runtime.setValue
@@ -44,6 +45,10 @@ import com.flipcash.app.messenger.internal.ChatViewModel
 import com.flipcash.app.messenger.internal.GroupInviteViewModel
 import com.flipcash.app.core.chat.InviteLinkAction
 import com.flipcash.app.core.chat.NewInviteLinkChoice
+import com.flipcash.app.core.chat.PinnedMessageJump
+import com.flipcash.app.messenger.internal.pins.PinnedRow
+import com.flipcash.app.messenger.internal.pins.pinnedListDone
+import com.flipcash.app.messenger.internal.screens.components.PinnedMessagesSheet
 import com.flipcash.app.messenger.internal.invites.InviteLinkActions
 import com.flipcash.app.messenger.internal.invites.NewInviteLinkContent
 import com.flipcash.app.messenger.internal.invites.toChoice
@@ -334,6 +339,9 @@ private fun chatEntryProvider(
     annotatedEntry<ChatStep.Reactors> { step ->
         FlowReactorsScreen(step.chatId, step.messageId)
     }
+    annotatedEntry<ChatStep.PinnedMessages> { step ->
+        FlowPinnedMessagesSheet(step.pinAfterUnpin)
+    }
 }
 
 @Composable
@@ -837,6 +845,39 @@ private fun FlowReactionPickerScreen(messageId: Long) {
     )
 }
 
+/**
+ * [ChatStep.PinnedMessages]: the conversation's pins on the app's sheet scene (L1, L1c, and L1b when
+ * [pinAfterUnpin] is set). The pins are the conversation's own, so this reads its view model; a
+ * tapped row closes the sheet and returns to the conversation as a [PinnedMessageJump].
+ */
+@Composable
+private fun FlowPinnedMessagesSheet(pinAfterUnpin: Long?) {
+    val viewModel = flowSharedViewModel<ChatViewModel>()
+    val state by viewModel.stateFlow.collectAsStateWithLifecycle()
+    val dismissSheet = LocalBottomSheetDismissDispatcher.current
+    val resultBack = resultBackNavigator<PinnedMessageJump>(exit = dismissSheet)
+
+    // Built off the main thread: a cash row looks up its token before it can draw.
+    val rows by produceState<List<PinnedRow>?>(null, state.pins) { value = viewModel.pinnedRows(state.pins) }
+    // The last rows stay up while the sheet slides away, so it never empties on the way out.
+    var shownRows by remember { mutableStateOf<List<PinnedRow>>(emptyList()) }
+    rows?.takeIf { it.isNotEmpty() }?.let { shownRows = it }
+
+    // The last unpin, or the waiting message landing in the slot it freed, leaves nothing to do here.
+    val done = state.pins.pinnedListDone(pinAfterUnpin)
+    LaunchedEffect(done) { if (done) dismissSheet() }
+
+    PinnedMessagesSheet(
+        rows = shownRows,
+        canUnpin = state.canPin,
+        full = pinAfterUnpin != null,
+        fullQuote = state.waitingPin?.takeIf { it.messageId == pinAfterUnpin }?.quote,
+        onOpen = { resultBack.returnValue(PinnedMessageJump(it)) },
+        onUnpin = { viewModel.dispatchEvent(ChatViewModel.Event.UnpinMessage(it, pinAfter = pinAfterUnpin)) },
+        onClose = { dismissSheet() },
+    )
+}
+
 /**
  * Who reacted to [messageId], and with what, from the entry's own [ReactorsViewModel]. Tapping a
  * named row dismisses this sheet, then opens that person's profile on the chat.