Drop a conversation from the list when its last message is removed

e2e/specs/delivery.spec.ts

@@ -60,6 +60,9 @@ const message = (page: Page, text: string) => page.locator(".room__item").filter
 
 const bubble = (page: Page, text: string) => page.locator(".chat-bubble").filter({hasText: text})
 
+// One conversation in the sidebar list is one button; nothing inside it is one.
+const chatItems = (page: Page) => page.locator(".secondary-nav .overflow-auto").locator("button")
+
 // One toast at a time — src/app/toast.ts holds a single writable — so this is the toast.
 const toast = (page: Page) => page.getByRole("alert")
 
@@ -230,6 +233,10 @@ test("US-068 watch a delayed send, and cancel it", async ({seed, as}) => {
 
   await toast(alice).getByRole("button", {name: "Cancel"}).click()
 
+  // That was her only message to him, so the conversation goes with it rather than staying in
+  // the list with nothing left to name it by.
+  await expect(chatItems(alice)).toHaveCount(0)
+
   await send(alice, "actually, hi")
 
   await expect(bubble(bob, "actually, hi")).toBeVisible()

src/app/chats.ts

@@ -100,12 +100,18 @@ export const chatsById = call(() => {
       // (unlike a delete, which leaves the target flagged), so `getEvent` would return nothing and
       // the message would linger. Replace each affected chat with a fresh object rather than mutating
       // its messages in place: deriveChat is deduplicated by reference (see makeDeriveItem/
-      // deriveDeduplicated), so a chat whose identity is unchanged never reaches the ui.
+      // deriveDeduplicated), so a chat whose identity is unchanged never reaches the ui. A chat
+      // that loses its last message goes with it, since a chat is only ever its messages.
       for (const [chatId, chat] of chatsById) {
         const messages = chat.messages.filter(e => !removed.has(e.id))
 
         if (messages.length !== chat.messages.length) {
-          chatsById.set(chatId, {...chat, messages})
+          if (messages.length > 0) {
+            chatsById.set(chatId, {...chat, messages})
+          } else {
+            chatsById.delete(chatId)
+          }
+
           dirty = true
         }
       }

src/app/notifications.ts

@@ -261,11 +261,9 @@ export const latestActivityByPath = derived(
     const activity = new Map<string, Activity>()
 
     for (const {pubkeys, messages} of $chatsById.values()) {
-      if (messages[0]) {
-        const path = makeChatPath(pubkeys)
+      const path = makeChatPath(pubkeys)
 
-        activity.set(path, {path, pubkeys, event: messages[0]})
-      }
+      activity.set(path, {path, pubkeys, event: messages[0]})
     }
 
     const roomList = $app.user?.pubkey ? $roomLists.get($app.user.pubkey) : undefined