Fix chat composer scroll

TFM/Features/AI/ConversationViews.swift

@@ -91,6 +91,71 @@ struct TextViewMarkedTextObserver: NSViewRepresentable {
     }
 }
 
+/// Makes AppKit hide the TextEditor's vertical scroller while its document fits.
+///
+/// SwiftUI's scroll-indicator visibility does not remove the disabled scroller
+/// from a macOS TextEditor when the system is configured to always show scroll
+/// bars. The underlying NSScrollView already knows whether its document exceeds
+/// the clip view, so leave that decision to `autohidesScrollers` instead of
+/// duplicating it from the composer's approximate text-height measurement.
+struct TextEditorScrollViewConfigurator: NSViewRepresentable {
+    final class ResolverView: NSView {
+        override func viewDidMoveToWindow() {
+            super.viewDidMoveToWindow()
+            configureAfterLayout()
+        }
+
+        override func layout() {
+            super.layout()
+            configureScrollView()
+        }
+
+        func configureAfterLayout() {
+            Task { @MainActor [weak self] in self?.configureScrollView() }
+        }
+
+        private func configureScrollView() {
+            guard let contentView = window?.contentView, !bounds.isEmpty,
+                let scrollView = textEditorScrollView(in: contentView)
+            else { return }
+
+            guard !scrollView.autohidesScrollers || !scrollView.hasVerticalScroller else { return }
+            scrollView.hasVerticalScroller = true
+            scrollView.autohidesScrollers = true
+            scrollView.tile()
+        }
+
+        private func textEditorScrollView(in root: NSView) -> NSScrollView? {
+            let targetFrame = convert(bounds, to: root)
+            let targetCenter = NSPoint(x: targetFrame.midX, y: targetFrame.midY)
+            return descendantScrollViews(in: root).first { scrollView in
+                guard let textView = scrollView.documentView as? NSTextView, textView.isEditable else {
+                    return false
+                }
+                return scrollView.convert(scrollView.bounds, to: root).contains(targetCenter)
+            }
+        }
+
+        private func descendantScrollViews(in root: NSView) -> [NSScrollView] {
+            var result: [NSScrollView] = []
+            func visit(_ view: NSView) {
+                if let scrollView = view as? NSScrollView { result.append(scrollView) }
+                view.subviews.forEach(visit)
+            }
+            visit(root)
+            return result
+        }
+    }
+
+    func makeNSView(context: Context) -> ResolverView {
+        ResolverView(frame: .zero)
+    }
+
+    func updateNSView(_ nsView: ResolverView, context: Context) {
+        nsView.configureAfterLayout()
+    }
+}
+
 // MARK: - Context chips
 
 /// The row of user-visible attachments sent to the LLM endpoint.
@@ -609,10 +674,6 @@ struct ComposerView: View {
         TextEditor(text: draft)
             .font(.body)
             .scrollContentBackground(.hidden)
-            .scrollIndicators(
-                draftHeight > maximumDraftHeight ? .automatic : .hidden,
-                axes: .vertical
-            )
             .focused($isFocused)
             .overlay(alignment: .topLeading) {
                 if draft.wrappedValue.isEmpty, !hasMarkedText {
@@ -643,6 +704,7 @@ struct ComposerView: View {
                     paste: { isFocused && handleContextPaste() }
                 )
             }
+            .background { TextEditorScrollViewConfigurator() }
             .onPasteCommand(of: [.fileURL, .image, .text]) { _ in
                 if !handleContextPaste() { insertShortPasteIntoEditor() }
             }

TFMTests/ChatComposerStateTests.swift

@@ -1,5 +1,7 @@
 import AgentKit
+import AppKit
 import Foundation
+import SwiftUI
 import TermindApplication
 import TermindDomain
 import TermindInfrastructure
@@ -51,6 +53,42 @@ private actor ConversationCancellationProbe {
 @Suite
 @MainActor
 struct ChatComposerStateTests {
+    @Test
+    func textEditorScrollerAppearsOnlyWhenItsDocumentOverflows() async throws {
+        let state = ComposerScrollerTestState()
+        let hosting = NSHostingView(
+            rootView: ComposerScrollerTestView(state: state)
+                .frame(width: 320, height: 80)
+        )
+        let window = NSWindow(
+            contentRect: NSRect(x: 0, y: 0, width: 320, height: 80),
+            styleMask: .borderless,
+            backing: .buffered,
+            defer: false
+        )
+        window.isReleasedWhenClosed = false
+        window.contentView = hosting
+        defer { window.close() }
+
+        let emptyScroller = try await requireComposerScroller(in: hosting)
+        #expect(emptyScroller.autohidesScrollers)
+        #expect(emptyScroller.hasVerticalScroller)
+        #expect(emptyScroller.verticalScroller?.isHidden == true)
+        #expect(emptyScroller.verticalScroller?.isEnabled == false)
+
+        state.text = Array(repeating: "A line of composer text", count: 40).joined(separator: "\n")
+        let overflowingScroller = try await requireComposerScroller(in: hosting) {
+            $0.verticalScroller?.isEnabled == true
+        }
+        #expect(overflowingScroller.autohidesScrollers)
+
+        state.text = "Short again"
+        let shortScroller = try await requireComposerScroller(in: hosting) {
+            $0.verticalScroller?.isEnabled == false
+        }
+        #expect(shortScroller.verticalScroller?.isHidden == true)
+    }
+
     @Test
     func largePasteThresholdUsesCharactersOrLines() {
         #expect(!ContextAttachmentImporter.shouldAttachPastedText(String(repeating: "x", count: 1_999)))
@@ -2212,3 +2250,55 @@ struct ChatComposerStateTests {
         }
     }
 }
+
+@Observable
+@MainActor
+private final class ComposerScrollerTestState {
+    var text = ""
+}
+
+private struct ComposerScrollerTestView: View {
+    @Bindable var state: ComposerScrollerTestState
+
+    var body: some View {
+        TextEditor(text: $state.text)
+            .background { TextEditorScrollViewConfigurator() }
+    }
+}
+
+@MainActor
+private func requireComposerScroller(
+    in root: NSView,
+    condition: (NSScrollView) -> Bool = { _ in true }
+) async throws -> NSScrollView {
+    for _ in 0..<100 {
+        root.layoutSubtreeIfNeeded()
+        if let scrollView = composerScrollViews(in: root).first(where: condition),
+            scrollView.autohidesScrollers
+        {
+            return scrollView
+        }
+        try await Task.sleep(for: .milliseconds(10))
+    }
+    Issue.record("The configured composer scroll view did not reach the expected state")
+    throw ComposerScrollerTestError.expectedStateNotReached
+}
+
+private func composerScrollViews(in root: NSView) -> [NSScrollView] {
+    var result: [NSScrollView] = []
+    func visit(_ view: NSView) {
+        if let scrollView = view as? NSScrollView,
+            let textView = scrollView.documentView as? NSTextView,
+            textView.isEditable
+        {
+            result.append(scrollView)
+        }
+        view.subviews.forEach(visit)
+    }
+    visit(root)
+    return result
+}
+
+private enum ComposerScrollerTestError: Error {
+    case expectedStateNotReached
+}