Transcript Incremental Projection

Nucleic-Session: 0FFD007B-0696-4517-9429-129C7B0FD5AC
Co-authored-by: Nucleic <[email protected]>

NucleicRemote/NucleicRemote/Views/SessionDetailView.swift

@@ -284,15 +284,6 @@ struct SessionDetailView: View {
     /// pending. Content scrolls beneath it; nothing renders when there's nothing to act on.
     private var actionArea: some View {
         VStack(spacing: 8) {
-            // The jump-to-bottom chevron rides here, immediately above the chat bar — not as a
-            // transcript overlay, which aligned to the scroll view's full-height bounds and so sat
-            // behind this floating bar at the screen's bottom edge. Shown only while scrolled up; a
-            // tap bumps the same scroll request the send button uses, so following resumes once the
-            // transcript reaches the bottom. Mirrors the Mac's `JumpToBottomButton`.
-            if !isScrolledToBottom {
-                JumpToBottomButton { scrollToBottomRequest += 1 }
-                    .transition(.move(edge: .bottom).combined(with: .opacity))
-            }
             // Interacting with a chat while the owning Mac is unreachable surfaces this first, so a
             // disabled composer reads as "offline / read-only history" rather than broken.
             if !store.connectivity.isLive { disconnectedBanner }
@@ -300,6 +291,27 @@ struct SessionDetailView: View {
         }
         .padding(.horizontal, 12)
         .padding(.bottom, 8)
+        // The jump-to-bottom chevron floats just above the chat bar as an *overlay* — deliberately
+        // not a stack member. This whole action area is the transcript's bottom `safeAreaInset`,
+        // so a stack-member chevron changed the scroll view's bottom inset by ~38pt every time it
+        // appeared — and its visibility is *decided by* that same scroll geometry
+        // (`isScrolledToBottom`). That geometry→chevron→geometry cycle could oscillate every
+        // frame near the follow threshold, re-layouting the whole eager transcript each time and
+        // pinning the main thread at 100% with the UI locked. An overlay contributes nothing to
+        // the inset height, so showing or hiding it can't move the scroll geometry at all.
+        // (It's not a transcript overlay either — that aligned to the scroll view's full-height
+        // bounds and sat behind this floating bar at the screen's bottom edge.) A tap bumps the
+        // same scroll request the send button uses, so following resumes once the transcript
+        // reaches the bottom. Mirrors the Mac's `JumpToBottomButton`.
+        .overlay(alignment: .top) {
+            if !isScrolledToBottom {
+                JumpToBottomButton { scrollToBottomRequest += 1 }
+                    // Hang the button *above* the bar: report its bottom edge (plus a gap) as its
+                    // top guide, so the overlay's top alignment places it outside the bar's bounds.
+                    .alignmentGuide(.top) { $0[.bottom] + 8 }
+                    .transition(.move(edge: .bottom).combined(with: .opacity))
+            }
+        }
         .animation(.easeInOut(duration: 0.15), value: isScrolledToBottom)
     }