# Suspense Boundaries & Streaming Design

**Date:** 2026-05-16
**Status:** Approved

## Problem

The home feed page (`app/page.tsx`) blocks rendering until all data is ready:
- `getFeed` + `getMe` — critical path, fine
- `getFriends` + `getTopFriends` — sidebar data, runs **after** the feed fetch, adds 150–500ms before any HTML ships
- `PopularTags`, `TopFriends`, `UsersCount` are async server components that all resolve before the page renders

Additionally, `TopFriends` has an N+1 problem: it fetches a list of usernames then makes N separate `getUserProfile` calls in parallel (~500ms–2s+ for 5–10 friends).

No React Suspense boundaries exist anywhere in the app. `ThoughtSkeleton` and `ProfileSkeleton` are available from the previous overhaul.

## Solution

1. **Backend:** enrich `/users/{username}/top-friends` to return full `UserResponse` objects — eliminating the N+1
2. **Frontend:** move sidebar fetches into the sidebar components themselves, wrap each in `<Suspense>`, strip secondary fetches from `app/page.tsx`

---

## Section 1: Backend — Enrich top-friends endpoint

### Response type change

```rust
// crates/api-types/src/responses.rs
pub struct TopFriendsResponse {
    pub top_friends: Vec<UserResponse>,
}
```

Replaces the existing `{ topFriends: string[] }` shape. Same URL: `GET /users/{username}/top-friends`.

### Use case change

The existing use case calls `TopFriendRepository::get_top_friends(username)` returning `Vec<UserId>`. Add a `UserRepository::find_many(&[UserId])` call (or a single JOIN query) to resolve the full user objects in one extra query. No N+1.

### Files changed

| File | Change |
|---|---|
| `crates/api-types/src/responses.rs` | Add `TopFriendsResponse { top_friends: Vec<UserResponse> }` |
| `crates/domain/src/ports.rs` | Add `find_many(ids: &[UserId])` to `UserRepository` (or equivalent) |
| `crates/adapters/postgres/src/user.rs` | Implement `find_many` with `WHERE id = ANY($1)` |
| `crates/application/src/use_cases/users.rs` | Update top-friends use case to return `Vec<User>` |
| `crates/presentation/src/handlers/users.rs` | Map `Vec<User>` → `TopFriendsResponse` |

---

## Section 2: Frontend — Suspense boundaries + self-contained sidebars

### Strip `app/page.tsx`

Remove `getFriends`, `getTopFriends`, `shouldDisplayTopFriends`, and the conditional sidebar rendering logic. Page-level critical path becomes:

```ts
const [feedData, me] = await Promise.all([
  getFeed(token, page).catch(() => null),
  getMe(token).catch(() => null),
])
```

Pass `me.username` and `token` as props to `TopFriends`.

### Self-contained `TopFriends`

`TopFriends` receives `username: string` and `token: string` as props and fetches `getTopFriends(username, token)` internally. The response is now `{ topFriends: UserResponse[] }` — render directly, no secondary fetches.

### Suspense wrapping (both desktop and mobile sidebars)

```tsx
<Suspense fallback={<ProfileSkeleton />}>
  <TopFriends username={me.username} token={token} />
</Suspense>
<Suspense fallback={<TagsSkeleton />}>
  <PopularTags />
</Suspense>
<Suspense fallback={<CountSkeleton />}>
  <UsersCount />
</Suspense>
```

Each widget streams in independently. Feed renders as soon as `getFeed` resolves.

### New skeleton variants

Add to `components/loading-skeleton.tsx`:

```tsx
export function TagsSkeleton() {
  return (
    <Card>
      <CardContent className="pt-4 space-y-2">
        <Skeleton className="h-4 w-24" />
        {[...Array(5)].map((_, i) => (
          <Skeleton key={i} className="h-6 w-full rounded-full" />
        ))}
      </CardContent>
    </Card>
  )
}

export function CountSkeleton() {
  return (
    <Card>
      <CardContent className="pt-4">
        <Skeleton className="h-6 w-32" />
      </CardContent>
    </Card>
  )
}
```

### `loading.tsx` files for pages missing them

Currently only `/users/[username]/loading.tsx` exists. Add:

| Page | Skeleton content |
|---|---|
| `app/loading.tsx` | `ThoughtSkeleton` × 3 |
| `app/tags/[tagName]/loading.tsx` | `ThoughtSkeleton` × 3 |
| `app/search/loading.tsx` | `ThoughtSkeleton` × 3 |
| `app/thoughts/[thoughtId]/loading.tsx` | `ThoughtSkeleton` × 2 |

### Update `lib/api.ts`

```ts
// Before
export const getTopFriends = (username: string, token: string | null) =>
  apiFetch(..., z.object({ topFriends: z.array(z.string()) }), token)

// After
export const getTopFriends = (username: string, token: string | null) =>
  apiFetch(..., z.object({ topFriends: z.array(UserSchema) }), token)
```

---

## Files Changed

### Backend

| File | Change |
|---|---|
| `crates/api-types/src/responses.rs` | `TopFriendsResponse { top_friends: Vec<UserResponse> }` |
| `crates/domain/src/ports.rs` | `UserRepository::find_many` |
| `crates/adapters/postgres/src/user.rs` | `find_many` impl |
| `crates/application/src/use_cases/users.rs` | Return `Vec<User>` from top-friends use case |
| `crates/presentation/src/handlers/users.rs` | Map to `TopFriendsResponse` |

### Frontend

| File | Change |
|---|---|
| `thoughts-frontend/lib/api.ts` | Update `getTopFriends` schema |
| `thoughts-frontend/app/page.tsx` | Strip sidebar fetches; pass `username`+`token` to TopFriends |
| `thoughts-frontend/components/top-friends.tsx` | Self-contained fetch; use `UserResponse[]` |
| `thoughts-frontend/components/loading-skeleton.tsx` | Add `TagsSkeleton`, `CountSkeleton` |
| `thoughts-frontend/app/loading.tsx` | New — feed skeleton |
| `thoughts-frontend/app/tags/[tagName]/loading.tsx` | New |
| `thoughts-frontend/app/search/loading.tsx` | New |
| `thoughts-frontend/app/thoughts/[thoughtId]/loading.tsx` | New |

---

## What This Does Not Cover

- Suspense on the feed content itself (feed is already the critical path — streaming it would show partial thought lists, which is awkward UX)
- Left sidebar "Filters & Sorting" placeholder (still empty)
- Streaming on other pages beyond loading.tsx coverage