docs: document tweet conversations

docs/superpowers/specs/2026-07-13-twitter-lite-design.md

@@ -33,6 +33,7 @@ The product reduces ambient discovery rather than limiting how far a deliberate
 - raw X search syntax;
 - `Top` and `Latest` search products;
 - `filter:follows` search filtering;
+- deliberate post detail pages with cursor-paginated visible conversations;
 - photos, videos, animated GIFs, quoted posts, article previews, and engagement counts when supplied by Bird;
 - infinite cursor pagination;
 - explicit retry, empty, error, loading, and end states;
@@ -46,6 +47,7 @@ The product reduces ambient discovery rather than limiting how far a deliberate
 - all X mutation operations;
 - user autocomplete and typeahead;
 - People and Media search products;
+- related-post feeds and automatic post discovery;
 - a generic relay proxy;
 - deployment beyond a personal localhost process.
 
@@ -105,6 +107,7 @@ TanStack Start supplies the browser/server boundary. Bird is imported only by se
 
 - `/user?target=<handle-or-url>` displays the User tab.
 - `/search?q=<query>&product=<Top|Latest>&following=<boolean>` displays the Search tab.
+- `/status/:tweetId` displays one selected post and its visible conversation.
 - `/` redirects to `/user` without a target.
 
 The target, query, product, and following flag are validated typed search parameters. Cursor state is internal to TanStack Query because it is transport state rather than a user-controlled view setting.
@@ -125,7 +128,7 @@ new TwitterClient({
 
 `TWITTER_RELAY_BASE_URL` is required. `BIRD_PROFILE_NAME` is optional but must be passed explicitly because the Bird library does not read that environment variable itself.
 
-Only two server functions are callable by the application:
+Only three server functions are callable by the application:
 
 ```ts
 type PostPage = {
@@ -144,8 +147,18 @@ searchPosts(input: {
   following: boolean
   cursor?: string
 }): Promise<PostPage>
+
+loadThreadPosts(input:
+  | { tweetId: string }
+  | { tweetId: string; conversationId: string; cursor: string }
+): Promise<ThreadPage>
 ```
 
+The status route and `loadThreadPosts` contract are specified in
+`2026-07-13-tweet-detail-thread-design.md`. Conversation reads compose Bird's
+existing `getTweet()` and `getThreadPaged()` methods; they add no Bird or relay
+operation.
+
 Neither function exposes the Bird client, arbitrary method names, arbitrary relay URLs, or mutation operations.
 
 ### User Timeline Flow
@@ -174,6 +187,10 @@ The first request fetches 20 posts. An IntersectionObserver sentinel near the li
 
 Flattened pages are deduplicated by post ID while preserving API order. A failed later page leaves all previously loaded posts visible and presents one explicit Retry control. Requests do not retry automatically.
 
+User and search pages preserve API order. Conversation pages preserve Bird's
+current order: chronological within a fetched page, with cursor pages appended
+in retrieval order.
+
 ## Interface Design
 
 ### Layout