fix(macos): fold only user messages, never replies

macos/Sources/RustCode/DebugDriver.swift

@@ -372,23 +372,21 @@ enum DebugDriver {
             }
             report("toolstream \(steps): row \(row) from \(Int(start)) scrolled \(Int(scrolled)), now \(Int(last)), worst stray \(Int(worst)), lost \(lost) of \(steps * 2) checks")
         case "fold":
-            // `fold [user|reply] [up]`: opens or folds the first long message
-            // of that kind in view, as its Show more control does (#2303);
+            // `fold [user] [up]`: opens or folds the first long user message
+            // in view, as its Show more control does (#2303);
             // with `up`, the chat is first scrolled so the message's top is
             // above the view. Reports where its top and end are in the view
             // before and over the next frames: opening and folding keep its
             // top, folding one whose top is above keeps its end.
             guard let state = ChatScrollState.current else { break }
-            let wantsUser = parts.count < 2 || parts[1] != "reply"
             let window = NSApp.windows.first { $0.isVisible && $0.contentView != nil }
             func frame(_ id: Int) -> (top: Int, end: Int)? {
                 guard let top = state.debugScreenTop(id), let height = state.debugFrame(id)?.height else { return nil }
                 return (Int(top), Int(top + height))
             }
             let candidates = model.transcript.items.filter { item in
                 switch item.content {
-                case .user(let text): wantsUser && MessageCollapse.mayBeLong(text)
-                case .assistant(let text): !wantsUser && MessageCollapse.mayBeLong(text)
+                case .user(let text): MessageCollapse.mayBeLong(text)
                 default: false
                 }
             }

macos/Sources/RustCode/TranscriptRows.swift

@@ -238,7 +238,7 @@ private struct AssistantMessage: View {
     var body: some View {
         let parsed = parsed
         VStack(alignment: .leading, spacing: 10) {
-            FoldingMessage(id: id, text: text, folds: MessageCollapse.folds(.assistant(text), isStreaming: isStreaming),
+            FoldingMessage(id: id, text: text, folds: false,
                            isExpanded: isExpanded) {
                 VStack(alignment: .leading, spacing: 10) {
                     ForEach(Array(parsed.blocks.enumerated()), id: \.offset) { index, block in

macos/Sources/RustCodeKit/MessageCollapse.swift

@@ -2,10 +2,10 @@ import Foundation
 
 /// Long chat messages fold to their first lines behind Show more (#2303).
 ///
-/// A user message or a finished reply taller than `maxLines` lines, and the
-/// Show more control, shows its first `maxLines` lines under a fade. Only
-/// the drawing changes: copy, the message menu, find and VoiceOver still get
-/// the whole text. A reply never folds while it is written.
+/// A user message taller than `maxLines` lines, and the Show more control,
+/// shows its first `maxLines` lines under a fade. Only the drawing changes:
+/// copy, the message menu, find and VoiceOver still get the whole text.
+/// Replies never fold.
 public enum MessageCollapse {
     /// The lines a folded message shows.
     public static let maxLines = 12
@@ -15,14 +15,10 @@ public enum MessageCollapse {
     /// The height of the Show more control under a folded message.
     public static let controlHeight: Double = 22
 
-    /// Whether a message of this kind folds when it is long: what the reader
-    /// wrote and finished replies, never a reply still being written.
-    public static func folds(_ content: TranscriptItem.Content, isStreaming: Bool) -> Bool {
-        switch content {
-        case .user: true
-        case .assistant: !isStreaming
-        case .thinking, .tool, .command: false
-        }
+    /// Whether a message of this kind folds when it is long: only what the
+    /// reader wrote.
+    public static func folds(_ content: TranscriptItem.Content) -> Bool {
+        if case .user = content { true } else { false }
     }
 
     /// Whether `text` may run past `maxLines` lines: each line wraps every

macos/Tests/RustCodeKitTests/MessageCollapseTests.swift

@@ -37,13 +37,11 @@ final class MessageCollapseTests: XCTestCase {
         XCTAssertTrue(MessageCollapse.isLong(height: 100 * line, lineHeight: line))
     }
 
-    func testRepliesNeverFoldWhileWritten() {
-        XCTAssertTrue(MessageCollapse.folds(.user("hi"), isStreaming: false))
-        XCTAssertTrue(MessageCollapse.folds(.user("hi"), isStreaming: true))
-        XCTAssertTrue(MessageCollapse.folds(.assistant("hi"), isStreaming: false))
-        XCTAssertFalse(MessageCollapse.folds(.assistant("hi"), isStreaming: true))
-        XCTAssertFalse(MessageCollapse.folds(.thinking("hi"), isStreaming: false))
-        XCTAssertFalse(MessageCollapse.folds(.command(input: "/x", output: lines(40)), isStreaming: false))
+    func testOnlyUserMessagesFold() {
+        XCTAssertTrue(MessageCollapse.folds(.user("hi")))
+        XCTAssertFalse(MessageCollapse.folds(.assistant(lines(40))))
+        XCTAssertFalse(MessageCollapse.folds(.thinking("hi")))
+        XCTAssertFalse(MessageCollapse.folds(.command(input: "/x", output: lines(40))))
     }
 
     func testReplayedMessagesStartFoldedAndOpenPerChat() {