Merge nucleic/plucky-fern-dingo into dev

Chat: open existing sessions already scrolled to the bottom (no scroll
animation) via .defaultScrollAnchor(.bottom).

Sources/NucleicApp/SessionDetailView.swift

@@ -15,6 +15,13 @@ struct SessionDetailView: View {
     @State private var summaryExpanded = false
     /// The user message awaiting a "revert to here" confirmation (its canonical `seq`).
     @State private var revertSeq: UInt64?
+    /// Set when a session is opened; the next transcript load jumps to the bottom
+    /// without animation so an existing chat appears already scrolled down. The
+    /// transcript loads asynchronously after `openSessionID` changes, so the
+    /// instant jump has to ride the first content arrival, not the id change.
+    /// Starts armed so the first navigation into a chat (which creates this view
+    /// fresh, with no `openSessionID` change to observe) also lands at the bottom.
+    @State private var pendingOpenScroll = true
     @AppStorage(TranscriptDisplay.showDebugKey) private var showDebugLines = false
     @AppStorage(SubmitKeyMode.storageKey) private var submitKeyRaw = SubmitKeyMode.returnSends.rawValue
 
@@ -394,9 +401,25 @@ struct SessionDetailView: View {
                 .padding(.top, 14)
                 .frame(maxWidth: .infinity)
             }
+            // Anchor initial layout at the bottom so an opened chat renders already
+            // scrolled down — without this the ScrollView lays out at the top first,
+            // producing a visible top-then-scroll flash on open.
+            .defaultScrollAnchor(.bottom)
             .scrollContentBackground(.hidden)
-            .onChange(of: store.openTranscript.count) { _, _ in scrollToEnd(proxy) }
-            .onChange(of: store.openSessionID) { _, _ in scrollToEnd(proxy) }
+            .onChange(of: store.openTranscript.count) { _, _ in
+                // The first load after opening jumps instantly; later appends (new
+                // content while reading) animate as usual.
+                if pendingOpenScroll {
+                    pendingOpenScroll = false
+                    scrollToEnd(proxy, animated: false)
+                } else {
+                    scrollToEnd(proxy)
+                }
+            }
+            // Opening a session should land already scrolled down, not scroll into
+            // place after the fact. The transcript loads asynchronously, so arm the
+            // flag here and let the first content arrival do the instant jump.
+            .onChange(of: store.openSessionID) { _, _ in pendingOpenScroll = true }
             .onChange(of: isBusy) { _, busy in if busy { scrollToEnd(proxy) } }
         }
         // The visible summary floats in the top-right corner over the transcript;
@@ -415,10 +438,14 @@ struct SessionDetailView: View {
     private static let workingID = "nucleic.working-indicator"
     private static let bottomAnchorID = "nucleic.transcript-bottom"
 
-    private func scrollToEnd(_ proxy: ScrollViewProxy) {
+    private func scrollToEnd(_ proxy: ScrollViewProxy, animated: Bool = true) {
         // Always scroll to the trailing spacer, so the resting position shows the
         // last message with the full bottom padding beneath it.
-        withAnimation {
+        if animated {
+            withAnimation {
+                proxy.scrollTo(Self.bottomAnchorID, anchor: .bottom)
+            }
+        } else {
             proxy.scrollTo(Self.bottomAnchorID, anchor: .bottom)
         }
     }