refactor(mobile): read a send's not-sent snapshot as a Set

React Doctor flagged the array lookups inside the echo loops and an Array<…>
type; the snapshot is read as a Set and the type uses T[].

mobile/src/session/mobile-native-chat-draft-reconcile.ts

@@ -279,10 +279,7 @@ export function findLandedUnconfirmedSends(
   // (`[Image: source: …]` or no text) keys under '' so an empty-text send can
   // claim it.
   const messageIndexById = new Map<string, number>()
-  const userMessagesByText = new Map<
-    string,
-    Array<{ id: string; index: number; unsent: boolean }>
-  >()
+  const userMessagesByText = new Map<string, { id: string; index: number; unsent: boolean }[]>()
   for (const [index, message] of messages.entries()) {
     messageIndexById.set(message.id, index)
     if (message.role !== 'user') {
@@ -305,14 +302,14 @@ export function findLandedUnconfirmedSends(
     if (tailIndex === undefined) {
       continue
     }
-    const baselineUnsent = entry.baselineUnsentMessageIds ?? []
+    const baselineUnsent = new Set(entry.baselineUnsentMessageIds)
     const echo = userMessagesByText
       .get(entry.normalizedText)
       ?.find(
         (message) =>
           message.index > tailIndex &&
           !claimedMessageIds.has(message.id) &&
-          !(message.unsent && baselineUnsent.includes(message.id))
+          !(message.unsent && baselineUnsent.has(message.id))
       )
     if (echo) {
       claimedMessageIds.add(echo.id)

mobile/src/session/mobile-native-chat-pending-retirement.ts

@@ -160,11 +160,13 @@ export function retireLandedMobileNativeChatPending(
     }
   }
   // A not-sent row settles a send only when it appeared after the send: then it is the send's own.
-  const landedFor = (item: MobileNativeChatPendingMessage, text: string): number =>
-    (landedCounts.get(text) ?? 0) +
-    (unsentByText.get(text) ?? []).filter(
-      (id) => !(item.baselineUnsentMessageIds ?? []).includes(id)
-    ).length
+  const landedFor = (item: MobileNativeChatPendingMessage, text: string): number => {
+    const baselineUnsent = new Set(item.baselineUnsentMessageIds)
+    return (
+      (landedCounts.get(text) ?? 0) +
+      (unsentByText.get(text) ?? []).filter((id) => !baselineUnsent.has(id)).length
+    )
+  }
   const landedPendingIds = new Set<string>()
   // Why a separate set: a barrier preserves adjacency after a landing consumed a whole
   // row. An image landing can share its row with the send glued after it, so treating it