Session View Animation

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

NucleicRemote/NucleicRemote/Views/SessionDetailView.swift

@@ -494,8 +494,40 @@ struct TranscriptList: View {
     /// settling — a `.task(id:)` debounces it to detect when the opening layout has come to rest.
     @State private var transcriptContentHeight: CGFloat = 0
 
+    /// Memoized transcript projection. `TranscriptProjection.build` folds the entire raw event
+    /// stream into rows on every read, but `body` re-evaluates far more often than `events`
+    /// actually changes: while the chat is opening, `onScrollGeometryChange` bumps
+    /// `transcriptContentHeight` on every settling-layout frame, and each bump re-runs `body` —
+    /// so the untouched event stream was re-folded dozens of times during the exact window the
+    /// tab bar is sliding away, starving that animation of the main thread and making the
+    /// load-in jitter. Reuse the last fold whenever the stream is unchanged. A class held in
+    /// `@State` so reading/updating it from `body` doesn't itself invalidate the view (SwiftUI
+    /// stores the reference and never diffs its interior).
+    private final class ProjectionCache {
+        /// The event stream is append-only with strictly increasing `seq`, so `(count, lastSeq)`
+        /// uniquely pins it; `firstSeq` guards the open reset (stream cleared to `[]`, then
+        /// refilled). The two display toggles are inputs to the fold, so they key it too.
+        private struct Key: Equatable {
+            var count: Int; var firstSeq: UInt64; var lastSeq: UInt64
+            var showRaw: Bool; var showLockEvents: Bool
+        }
+        private var key: Key?
+        private var value: [TranscriptItem] = []
+
+        func items(for events: [AgentEvent], showRaw: Bool, showLockEvents: Bool) -> [TranscriptItem] {
+            let k = Key(count: events.count, firstSeq: events.first?.seq ?? 0,
+                        lastSeq: events.last?.seq ?? 0, showRaw: showRaw, showLockEvents: showLockEvents)
+            if key == k { return value }
+            let built = TranscriptProjection.build(events, showRaw: showRaw, showLockEvents: showLockEvents)
+            key = k
+            value = built
+            return built
+        }
+    }
+    @State private var projectionCache = ProjectionCache()
+
     private var items: [TranscriptItem] {
-        TranscriptProjection.build(events, showRaw: showRaw, showLockEvents: showLockEvents)
+        projectionCache.items(for: events, showRaw: showRaw, showLockEvents: showLockEvents)
     }
 
     /// How much content may still sit below the viewport's bottom edge and still count as "at