feat(macos): render native visualization blocks in chat

docs/visualizations.md

@@ -116,6 +116,27 @@ live stream, committed scrollback chunks, and finalized history cells all
 draw the same rows through the same renderer. That renderer is cached by
 width and theme like any other assistant message.
 
+## macOS app
+
+The macOS app (`macos/`) renders the same schema with the same limits and
+fallback reasons. `RustCodeKit/Visualization.swift` parses and bounds the
+payload, and `RustCode/VisualizationView.swift` draws it in SwiftUI:
+
+- `bar_chart` uses Swift Charts. Hovering a bar highlights it and shows its
+  exact value.
+- `table` headers sort it: click once for ascending, again for descending.
+  Every row is kept so a sort covers the whole table, but at most 50 are
+  shown. `sort_by` sets the initial order.
+- `tree` branches collapse and expand. The first two levels start open.
+
+The card's Copy button and context menu copy the source fence. A block that
+is still streaming shows a "Building visualization…" placeholder. Invalid or
+unfinished blocks show the source with the same note as the TUI. Only
+assistant replies render widgets: command output, user messages and tool
+output keep the fence as code. The app advertises
+`clientCapabilities._meta.rustcode.visualizations = 1` in its ACP
+`initialize`.
+
 ## Assistant-only
 
 Only the assistant message renderer recognizes the fence. User messages,
@@ -141,6 +162,7 @@ prompt and its cached prefix do not change during a session. The default is
 | Frontend                          | Hint | How it is decided                                   |
 | --------------------------------- | ---- | --------------------------------------------------- |
 | TUI (local)                       | yes  | Set at startup                                      |
+| macOS app                         | yes  | Advertises the ACP capability below                 |
 | ACP client advertising support    | yes  | `clientCapabilities._meta.rustcode.visualizations >= 1` at `initialize` |
 | Any other ACP client              | no   | Capability absent, malformed, or `0`                |
 | Remote gateway, iOS, Rust desktop, remote TUI | no | Default                                |

macos/Sources/RustCode/ContentView.swift

@@ -525,7 +525,8 @@ private struct ChatView: View {
             ScrollView {
                 LazyVStack(alignment: .leading, spacing: 18) {
                     ForEach(model.transcript.items) { item in
-                        TranscriptRow(item: item, isCurrentMatch: model.showsFind && item.id == model.currentMatch).id(item.id)
+                        TranscriptRow(item: item, isCurrentMatch: model.showsFind && item.id == model.currentMatch,
+                                      isStreaming: isReplyStreaming && item.id == model.transcript.items.last?.id).id(item.id)
                     }
                     if model.busy, model.turnSession == model.selectedSession, !isAgentWriting {
                         WorkingIndicator()
@@ -701,6 +702,11 @@ private struct ChatView: View {
 
     private let bottomAnchor = "bottom"
 
+    /// The shown chat has a turn in progress, so its last reply may still grow.
+    private var isReplyStreaming: Bool {
+        model.busy && model.turnSession == model.selectedSession
+    }
+
     /// Visible reply text is streaming. Whitespace or a `<think>` section the
     /// model sends before its first words still counts as waiting, so
     /// "Working" stays up until then.

macos/Sources/RustCode/MarkdownText.swift

@@ -7,6 +7,10 @@ import SwiftUI
 /// them; code blocks, tables and rules stand on their own.
 struct MarkdownText: View {
     let text: String
+    /// Draw `rustcode-viz` blocks as widgets. Only assistant replies set it.
+    var visualizations = false
+    /// The reply is still streaming, so an unclosed visualization shows a placeholder.
+    var isStreaming = false
     @Environment(\.findQuery) private var findQuery
 
     private enum Segment {
@@ -16,7 +20,7 @@ struct MarkdownText: View {
 
     private var segments: [Segment] {
         var segments: [Segment] = []
-        for block in MarkdownBlock.parse(text) {
+        for block in MarkdownBlock.parse(text, visualizations: visualizations) {
             switch block {
             case .paragraph, .heading, .listItem, .quote:
                 if case .prose(let blocks) = segments.last {
@@ -111,6 +115,8 @@ struct MarkdownText: View {
             Divider().padding(.vertical, 4)
         case .image(let alt, let url):
             InlineImage(url: url, alt: alt)
+        case .visualization(let visualization):
+            VisualizationView(block: visualization, isStreaming: isStreaming)
         default:
             EmptyView()
         }

macos/Sources/RustCode/TranscriptRows.swift

@@ -4,6 +4,8 @@ import SwiftUI
 struct TranscriptRow: View {
     let item: TranscriptItem
     var isCurrentMatch = false
+    /// This is the reply the agent is still writing.
+    var isStreaming = false
 
     var body: some View {
         content
@@ -22,7 +24,7 @@ struct TranscriptRow: View {
     private var content: some View {
         switch item.content {
         case .user(let text): UserMessage(text: text)
-        case .assistant(let text): AssistantMessage(text: text)
+        case .assistant(let text): AssistantMessage(text: text, isStreaming: isStreaming)
         case .thinking(let text): ThinkingBlock(text: text)
         case .tool(let tool): ToolRow(tool: tool)
         case .command(let input, let output): CommandCard(input: input, output: output)
@@ -171,14 +173,15 @@ private struct UserBubble: View {
 /// Agent text, with `<think>` sections the engine leaves inline folded away.
 private struct AssistantMessage: View {
     let text: String
+    var isStreaming = false
     @Environment(\.messageActions) private var messageActions
 
     var body: some View {
         VStack(alignment: .leading, spacing: 10) {
             let (prose, summary) = AssistantSummary.split(text)
             ForEach(Array(AssistantBlock.parse(prose).enumerated()), id: \.offset) { _, block in
                 switch block {
-                case .markdown(let text): MarkdownText(text: text)
+                case .markdown(let text): MarkdownText(text: text, visualizations: true, isStreaming: isStreaming)
                 case .thinking(let text, _): ThinkingBlock(text: text)
                 }
             }