fix(user-flow): close offline-queue, export, session, ban & realtime gaps

Comprehensive user-flow review across guest/host/admin roles, then fixes with
e2e regression guards. Highlights:

- Offline upload queue auto-resumes on reconnect: network errors keep items
  pending (not error), 4xx are terminal (no infinite retry), quota exhaustion
  returns a distinct 413; queue cap + dedup.
- Export lifecycle: release atomically locks uploads; reopen invalidates and
  re-release regenerates the keepsake; workers claim their job atomically so a
  reopen->re-release can't corrupt the ZIP; startup re-spawns interrupted
  exports.
- Sessions slide on activity (no 30-day cliff); JWT expiry deferred to the
  revocable session row; sign-out-everywhere + revoke-on-PIN-reset.
- Ban always hides content (v_feed / find_visible_media / export filter
  is_banned) but stays a read-only ban per USER_JOURNEYS §10 — sessions are
  not revoked, read access + keepsake download preserved.
- Realtime: server-clock SSE delta cursor; event-closed/opened drive the UI
  live; feed_delta rate-limited; like returns {liked, like_count} to fix
  multi-device drift; lightbox live comments; diashow delta backfill.
- Forgotten-PIN in-app request flow; simultaneous same-name join returns 409;
  quota increment is transactional; operator floor.

Adds e2e/specs/10-flow-review/ (offline resume, export integrity, deterministic
anti-race guard) and updates existing specs for the new contracts.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/handlers/social.rs

@@ -2,7 +2,7 @@ use axum::extract::{Path, Query, State};
 use axum::http::StatusCode;
 use axum::Json;
 use chrono::{DateTime, Utc};
-use serde::Deserialize;
+use serde::{Deserialize, Serialize};
 use uuid::Uuid;
 
 use crate::auth::middleware::AuthUser;
@@ -12,11 +12,22 @@ use crate::models::hashtag::{self, Hashtag};
 use crate::models::upload::Upload;
 use crate::state::AppState;
 
+#[derive(Serialize)]
+pub struct LikeResponse {
+    /// The caller's like state *after* this toggle. The client sets `liked_by_me` from
+    /// this rather than blind-inverting local state — otherwise a second device (same
+    /// recovered user) drifts, since the `like-update` broadcast only carries `like_count`.
+    pub liked: bool,
+    /// Fresh like count, or `null` if the (best-effort) count query hiccuped. The client
+    /// keeps its current count when this is null rather than adopting a wrong number.
+    pub like_count: Option<i64>,
+}
+
 pub async fn toggle_like(
     State(state): State<AppState>,
     auth: AuthUser,
     Path(upload_id): Path<Uuid>,
-) -> Result<StatusCode, AppError> {
+) -> Result<Json<LikeResponse>, AppError> {
     // Check if user is banned
     let user = crate::models::user::User::find_by_id(&state.pool, auth.user_id)
         .await?
@@ -35,7 +46,7 @@ pub async fn toggle_like(
     // ("Event schließen") freezes *new uploads* only — likes, comments and
     // browsing stay open (USER_JOURNEYS §9.3, FEATURES capability matrix).
 
-    // Try to insert; if conflict, delete (toggle)
+    // Try to insert; if conflict, delete (toggle). `liked` = the caller's state afterwards.
     let result = sqlx::query(
         "INSERT INTO \"like\" (upload_id, user_id) VALUES ($1, $2)
          ON CONFLICT (upload_id, user_id) DO NOTHING",
@@ -45,7 +56,8 @@ pub async fn toggle_like(
     .execute(&state.pool)
     .await?;
 
-    if result.rows_affected() == 0 {
+    let liked = result.rows_affected() > 0;
+    if !liked {
         // Already liked — remove
         sqlx::query("DELETE FROM \"like\" WHERE upload_id = $1 AND user_id = $2")
             .bind(upload_id)
@@ -55,24 +67,29 @@ pub async fn toggle_like(
     }
 
     // Fresh count so feed clients can patch the single card in place instead of
-    // refetching page 1 (mirrors v_feed.like_count = COUNT(DISTINCT user_id)). The
-    // count + broadcast are a UI optimisation — the like itself is already committed,
-    // so a failure here must not fail the request. Swallow the error and skip the
-    // broadcast; the next event or a pull-to-refresh reconciles the count.
-    if let Ok(like_count) = sqlx::query_scalar::<_, i64>(
+    // refetching page 1 (mirrors v_feed.like_count = COUNT(DISTINCT user_id)). The like
+    // itself is already committed, so a failed count must not fail the request — but we
+    // also must NOT broadcast/return a bogus 0 (that would push like_count: 0 to every
+    // client until the next event). On error we skip the broadcast and return null.
+    let like_count = sqlx::query_scalar::<_, i64>(
         "SELECT COUNT(DISTINCT user_id) FROM \"like\" WHERE upload_id = $1",
     )
     .bind(upload_id)
     .fetch_one(&state.pool)
     .await
-    {
+    .ok();
+
+    if let Some(count) = like_count {
+        // Broadcast the new count so other clients patch their card. Only `like_count` is
+        // shared — each client's own `liked_by_me` only changes via its own toggle (which
+        // now reads it straight from this response).
         let _ = state.sse_tx.send(crate::state::SseEvent {
             event_type: "like-update".to_string(),
-            data: serde_json::json!({ "upload_id": upload_id, "like_count": like_count }).to_string(),
+            data: serde_json::json!({ "upload_id": upload_id, "like_count": count }).to_string(),
         });
     }
 
-    Ok(StatusCode::NO_CONTENT)
+    Ok(Json(LikeResponse { liked, like_count }))
 }
 
 #[derive(Deserialize, Default)]