Reels pre-gen: make dedup cache-key-aware so key changes regenerate

exists_fresh only matched (span, library, render_version, age), so a
cache-key change that doesn't bump RENDER_VERSION (e.g. the max_segments
alignment, or any future selection-logic tweak) left last night's ledger
row looking 'fresh' — the nightly run would skip and the orphaned reel
would persist. Dedup now compares the stored cache_key to the freshly
computed key (and confirms the mp4 exists), so a changed key forces a
regen within the freshness window. exists_fresh stays as the HTTP
endpoint's fast gate.

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

src/reels/mod.rs

@@ -1095,14 +1095,29 @@ async fn pregen_one(
     };
     let min_generated_at = now - (max_age_hours as i64 * 3600);
 
-    let is_fresh = {
+    // Skip only when a fresh ledger row points at THIS exact cache key (same
+    // media, params, render version) and its file still exists. Comparing the
+    // stored cache_key — not just (span, library) — means a key change from
+    // selection-logic/params drift that doesn't bump RENDER_VERSION still forces
+    // a regen within the freshness window, instead of leaving a stale row that
+    // points at an orphaned reel.
+    let already_current = {
         let mut dao = app_state.precomputed_reel_dao.lock().expect("lock");
-        dao.exists_fresh(&ctx, span, library, RENDER_VERSION as i32, min_generated_at)
+        matches!(
-            .unwrap_or(false)
+            dao.latest_for(&ctx, span, library),
+            Ok(Some(row))
+                if row.cache_key == key
+                    && row.render_version == RENDER_VERSION as i32
+                    && row.generated_at >= min_generated_at
+        ) && reel_mp4_path(app_state, &key).exists()
     };
 
-    if is_fresh {
+    if already_current {
-        log::info!("Fresh precomputed reel exists for span={}, skipping", span);
+        log::info!(
+            "Fresh precomputed reel already current for span={} key={}, skipping",
+            span,
+            key
+        );
         return Ok(());
     }