Transcript Incremental Projection

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

NucleicRemote/NucleicRemote/Views/SessionDetailView.swift

@@ -576,6 +576,26 @@ struct TranscriptList: View {
     /// the Mac's `bottomFollowThreshold`.
     private let bottomFollowThreshold: CGFloat = 24
 
+    /// How far a *user* scroll must move away from the bottom before following disengages. Wider
+    /// than the re-engage threshold above on purpose (hysteresis): the action bar's height isn't
+    /// constant (composer lines grow, the working row appears, the keyboard dismisses
+    /// interactively), and every inset change perturbs the scroll geometry by tens of points. A
+    /// single threshold read both ways let one such perturbation flip the gate, whose reactions
+    /// (anchor toggle, bar animation) perturbed the geometry again — an oscillation that
+    /// re-layouted the whole eager transcript every frame and pinned the main thread at 100%.
+    /// The band is wider than any bar-height delta, so only a deliberate scroll crosses it.
+    private let bottomUnfollowThreshold: CGFloat = 64
+
+    /// The live scroll phase, used to tell *user* scrolling (finger down / flick decelerating)
+    /// from programmatic motion (autoscroll animations, anchor re-pins, inset changes). Only a
+    /// user-driven phase may disengage bottom-following — a programmatic perturbation can only
+    /// ever re-engage it — which structurally breaks every geometry→state→geometry feedback
+    /// cycle: no chain of layout reactions can take the gate false and sustain itself.
+    @State private var scrollPhase: ScrollPhase = .idle
+    private var isUserScrolling: Bool {
+        scrollPhase == .tracking || scrollPhase == .interacting || scrollPhase == .decelerating
+    }
+
     var body: some View {
         ScrollViewReader { proxy in
             ScrollView {