Session View Animation

Nucleic-Session: A8FFA1A6-443F-444A-A735-C53958D7E570
Co-authored-by: Nucleic <[email protected]>

NucleicRemote/NucleicRemote/Views/SessionDetailView.swift

@@ -526,10 +526,36 @@ struct TranscriptList: View {
     }
     @State private var projectionCache = ProjectionCache()
 
+    /// The in-flight background Markdown pre-warm (below), cancelled when a newer one supersedes
+    /// it or the transcript goes away — so a long warm can't outlive the view or stack up behind
+    /// row churn.
+    @State private var prewarmTask: Task<Void, Never>?
+
     private var items: [TranscriptItem] {
         projectionCache.items(for: events, showRaw: showRaw, showLockEvents: showLockEvents)
     }
 
+    /// Kick off (or restart) the off-main Markdown pre-warm for the visible messages. `MarkdownText`
+    /// parses every prose line with `AttributedString(markdown:)` during the eager first layout — a
+    /// cost that lands on the main thread right as the session is pushed and the tab bar slides
+    /// away, jittering the load-in. Snapshot the message bodies here on the main actor (a cheap read
+    /// of the memoized projection), then parse them on a background task so that first layout finds
+    /// the caches already warm. Idempotent and self-cancelling; the parse results are the same
+    /// whichever thread fills the (thread-safe) caches.
+    private func prewarmMarkdown() {
+        let bodies: [String] = items.compactMap {
+            if case .message(_, let text) = $0.kind { return text } else { return nil }
+        }
+        guard !bodies.isEmpty else { return }
+        prewarmTask?.cancel()
+        prewarmTask = Task.detached(priority: .utility) {
+            for body in bodies {
+                if Task.isCancelled { return }
+                MarkdownText.prewarm(body)
+            }
+        }
+    }
+
     /// How much content may still sit below the viewport's bottom edge and still count as "at
     /// the bottom" — a little slack so streaming deltas and rounding never flip the gate. Mirrors
     /// the Mac's `bottomFollowThreshold`.