fix(chat): scale rich chat content with the font-size slider (#68)

The chat font-size slider only set `\.dynamicTypeSize` on the chat
root, but ScarfFont tokens are fixed-point (`Font.system(size: 14, …)`)
so dynamic type didn't reach bubble text, reasoning, tool chips, code
blocks, or markdown headings. Slider moved between 85%–130% with
little visible effect.

Plumb a separate `\.chatFontScale: Double` env value from
`RichChatView` and have the chat content views read it:

- `RichMessageBubble` — user bubble body, reasoning (disclosure +
  inline), REASONING label, token chip, tool-chip name, metadata
  footer.
- `MarkdownContentView` — paragraphs (now pinned to a scaled body
  font instead of inheriting), headings (1..5), inline-rendered code
  blocks, code-language label.
- `CodeBlockView` — code body and language label.

`ChatFontScale.{body, callout, caption, captionStrong, caption2,
mono, monoSmall, codeBlock, codeInline}(_ scale:)` helpers mirror
`ScarfFont`'s base sizes so scale = 1.0 is byte-for-byte identical
to today's UI; the slider now actually moves the visible chat text.

Other surfaces (settings, sidebar, etc.) still use the static
ScarfFont tokens — chat scaling stays scoped to the chat surface.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scarf/scarf/Core/Utilities/MarkdownContentView.swift

@@ -3,12 +3,22 @@ import SwiftUI
 struct MarkdownContentView: View {
     let content: String
 
+    /// Chat font scale plumbed from `RichChatView` (issue #68). Defaults
+    /// to 1.0 when this view is used outside the chat surface so other
+    /// callers see the un-scaled rendering.
+    @Environment(\.chatFontScale) private var chatFontScale: Double
+
     var body: some View {
         VStack(alignment: .leading, spacing: 6) {
             ForEach(Array(parseBlocks().enumerated()), id: \.offset) { _, block in
                 blockView(block)
             }
         }
+        // Paragraphs are rendered as plain `Text(AttributedString)` and
+        // inherit whatever font is set on the enclosing scope. Pin the
+        // scope to the scaled body font so the chat slider actually
+        // moves the visible text.
+        .font(ChatFontScale.body(chatFontScale))
     }
 
     @ViewBuilder
@@ -37,15 +47,19 @@ struct MarkdownContentView: View {
     // MARK: - Block Views
 
     private func headingView(level: Int, text: String) -> some View {
-        let font: Font = switch level {
-        case 1: .title.bold()
-        case 2: .title2.bold()
-        case 3: .title3.bold()
-        case 4: .headline
-        default: .subheadline.bold()
+        // Heading sizes scale with `chatFontScale` (issue #68). Bases
+        // mirror the SwiftUI semantic tokens we used previously
+        // (`.title` ≈ 28, `.title2` ≈ 22, `.title3` ≈ 20, `.headline`
+        // ≈ 17, `.subheadline` ≈ 15) so 100% matches today's UI.
+        let baseSize: CGFloat = switch level {
+        case 1: 28
+        case 2: 22
+        case 3: 20
+        case 4: 17
+        default: 15
         }
         return Text(MarkdownRenderer.inlineAttributedString(text))
-            .font(font)
+            .font(.system(size: baseSize * chatFontScale, weight: .semibold))
             .textSelection(.enabled)
             .padding(.top, level <= 2 ? 8 : 4)
     }
@@ -54,11 +68,11 @@ struct MarkdownContentView: View {
         VStack(alignment: .leading, spacing: 4) {
             if let lang = language, !lang.isEmpty {
                 Text(lang)
-                    .font(.caption2.bold())
+                    .font(ChatFontScale.caption2(chatFontScale).bold())
                     .foregroundStyle(.secondary)
             }
             Text(code)
-                .font(.system(.callout, design: .monospaced))
+                .font(ChatFontScale.codeInline(chatFontScale))
                 .textSelection(.enabled)
                 .frame(maxWidth: .infinity, alignment: .leading)
         }

scarf/scarf/Features/Chat/ChatDensitySettings.swift

@@ -106,4 +106,74 @@ enum ChatFontScale {
         let pct = Int((scale * 100).rounded())
         return "\(pct)%"
     }
+
+    // MARK: - Scaled font helpers
+    //
+    // ScarfFont's tokens are fixed-point (`Font.system(size: 14, …)`),
+    // so `.environment(\.dynamicTypeSize, …)` doesn't reach them — the
+    // Mac chat slider had no visible effect on bubbles, reasoning,
+    // tool chips, or code blocks (issue #68). These helpers mirror the
+    // ScarfFont base sizes, multiplied by the user's chat scale, and
+    // are used by `RichMessageBubble`, `MarkdownContentView`, and
+    // `CodeBlockView` in place of the static tokens. At scale = 1.0
+    // they're byte-for-byte identical to ScarfFont so the default UI
+    // is unchanged.
+
+    static func body(_ scale: Double) -> Font {
+        .system(size: 14 * scale, weight: .regular)
+    }
+
+    static func bodyEmph(_ scale: Double) -> Font {
+        .system(size: 14 * scale, weight: .medium)
+    }
+
+    static func callout(_ scale: Double) -> Font {
+        .system(size: 15 * scale, weight: .regular)
+    }
+
+    static func caption(_ scale: Double) -> Font {
+        .system(size: 12 * scale, weight: .regular)
+    }
+
+    static func captionStrong(_ scale: Double) -> Font {
+        .system(size: 12 * scale, weight: .semibold)
+    }
+
+    static func caption2(_ scale: Double) -> Font {
+        .system(size: 10 * scale, weight: .medium)
+    }
+
+    static func mono(_ scale: Double) -> Font {
+        .system(size: 13 * scale, weight: .regular, design: .monospaced)
+    }
+
+    static func monoSmall(_ scale: Double) -> Font {
+        .system(size: 12 * scale, weight: .regular, design: .monospaced)
+    }
+
+    /// Code-block body — matches `CodeBlockView`'s 12pt mono.
+    static func codeBlock(_ scale: Double) -> Font {
+        .system(size: 12 * scale, weight: .regular, design: .monospaced)
+    }
+
+    /// Inline code in markdown paragraphs — `.callout` (15pt) mono.
+    static func codeInline(_ scale: Double) -> Font {
+        .system(size: 15 * scale, weight: .regular, design: .monospaced)
+    }
+}
+
+// MARK: - Environment plumbing
+
+private struct ChatFontScaleKey: EnvironmentKey {
+    static let defaultValue: Double = ChatFontScale.default
+}
+
+extension EnvironmentValues {
+    /// Multiplier applied to chat content fonts. Set once on
+    /// `RichChatView`'s root so message bubbles, markdown paragraphs,
+    /// and code blocks scale together. Default 1.0 = today's UI.
+    var chatFontScale: Double {
+        get { self[ChatFontScaleKey.self] }
+        set { self[ChatFontScaleKey.self] = newValue }
+    }
 }

scarf/scarf/Features/Chat/Views/CodeBlockView.swift

@@ -7,12 +7,16 @@ struct CodeBlockView: View {
 
     @State private var copied = false
 
+    /// Chat font scale plumbed from `RichChatView` (issue #68). Defaults
+    /// to 1.0 outside the chat surface.
+    @Environment(\.chatFontScale) private var chatFontScale: Double
+
     var body: some View {
         VStack(alignment: .leading, spacing: 0) {
             if let language, !language.isEmpty {
                 HStack {
                     Text(language)
-                        .font(.caption2.bold())
+                        .font(ChatFontScale.caption2(chatFontScale).bold())
                         .foregroundStyle(.secondary)
                     Spacer()
                     copyButton
@@ -31,7 +35,7 @@ struct CodeBlockView: View {
 
             ScrollView(.horizontal, showsIndicators: false) {
                 Text(code)
-                    .font(.system(size: 12, design: .monospaced))
+                    .font(ChatFontScale.codeBlock(chatFontScale))
                     .foregroundStyle(Color(nsColor: NSColor(red: 0.85, green: 0.87, blue: 0.91, alpha: 1.0)))
                     .textSelection(.enabled)
                     .padding(.horizontal, 10)

scarf/scarf/Features/Chat/Views/RichChatView.swift

@@ -64,6 +64,11 @@ struct RichChatView: View {
         }
         .frame(minHeight: 0, idealHeight: 500, maxHeight: .infinity)
         .environment(\.dynamicTypeSize, ChatFontScale.dynamicTypeSize(for: fontScale))
+        // ScarfFont tokens are fixed-point so dynamicTypeSize alone
+        // doesn't move bubble / markdown / code-block text. Plumb the
+        // raw scale via `\.chatFontScale` so chat content views can
+        // read it and scale their explicit sizes too (issue #68).
+        .environment(\.chatFontScale, fontScale)
         // Animate side-pane shows/hides so the transcript reflows
         // smoothly rather than snapping. ~180ms feels responsive
         // without being jarring.

scarf/scarf/Features/Chat/Views/RichMessageBubble.swift

@@ -14,6 +14,11 @@ struct RichMessageBubble: View, Equatable {
 
     @Environment(ChatViewModel.self) private var chatViewModel
 
+    /// Chat-only font scale set on `RichChatView`. Chat content uses
+    /// these multiplied sizes (issue #68); other surfaces still see
+    /// the static ScarfFont tokens at scale = 1.0.
+    @Environment(\.chatFontScale) private var chatFontScale: Double
+
     /// Scarf-local chat density preferences (issues #47 / #48). All
     /// three default to today's UI. Read here so the reasoning + tool-
     /// call switches don't have to thread the values through every
@@ -68,7 +73,7 @@ struct RichMessageBubble: View, Equatable {
             HStack {
                 Spacer(minLength: 80)
                 Text(message.content)
-                    .scarfStyle(.body)
+                    .font(ChatFontScale.body(chatFontScale))
                     .foregroundStyle(ScarfColor.onAccent)
                     .textSelection(.enabled)
                     .padding(.horizontal, 14)
@@ -91,7 +96,7 @@ struct RichMessageBubble: View, Equatable {
                         .font(.system(size: 9))
                         .foregroundStyle(ScarfColor.success)
                     Text(time, style: .time)
-                        .font(ScarfFont.caption2)
+                        .font(ChatFontScale.caption2(chatFontScale))
                         .foregroundStyle(ScarfColor.foregroundFaint)
                 }
                 .padding(.trailing, 4)
@@ -183,7 +188,7 @@ struct RichMessageBubble: View, Equatable {
     private var reasoningDisclosure: some View {
         DisclosureGroup {
             Text(message.preferredReasoning ?? "")
-                .font(ScarfFont.monoSmall)
+                .font(ChatFontScale.monoSmall(chatFontScale))
                 .foregroundStyle(ScarfColor.foregroundMuted)
                 .italic()
                 .textSelection(.enabled)
@@ -194,11 +199,11 @@ struct RichMessageBubble: View, Equatable {
                 Image(systemName: "brain")
                     .font(.system(size: 11))
                 Text("REASONING")
-                    .scarfStyle(.captionStrong)
+                    .font(ChatFontScale.captionStrong(chatFontScale))
                     .tracking(0.5)
                 if let tokens = message.tokenCount, tokens > 0 {
                     Text("· \(tokens) tok")
-                        .font(ScarfFont.monoSmall)
+                        .font(ChatFontScale.monoSmall(chatFontScale))
                         .foregroundStyle(ScarfColor.foregroundFaint)
                 }
             }
@@ -222,7 +227,7 @@ struct RichMessageBubble: View, Equatable {
                 .font(.system(size: 9))
                 .foregroundStyle(ScarfColor.warning)
             Text(message.preferredReasoning ?? "")
-                .font(ScarfFont.caption)
+                .font(ChatFontScale.caption(chatFontScale))
                 .italic()
                 .foregroundStyle(ScarfColor.foregroundFaint)
                 .textSelection(.enabled)
@@ -281,7 +286,7 @@ struct RichMessageBubble: View, Equatable {
                             .font(.system(size: 10))
                             .foregroundStyle(color)
                         Text(call.functionName)
-                            .font(ScarfFont.monoSmall)
+                            .font(ChatFontScale.monoSmall(chatFontScale))
                             .fontWeight(.medium)
                             .foregroundStyle(ScarfColor.foregroundPrimary)
                             .lineLimit(1)
@@ -341,25 +346,26 @@ struct RichMessageBubble: View, Equatable {
         HStack(spacing: 8) {
             if let tokens = message.tokenCount, tokens > 0 {
                 Text("\(tokens) tok")
-                    .font(ScarfFont.monoSmall)
+                    .font(ChatFontScale.monoSmall(chatFontScale))
             }
             if let reason = message.finishReason, !reason.isEmpty {
                 Text("·")
                 Text(reason)
-                    .scarfStyle(.caption)
+                    .font(ChatFontScale.caption(chatFontScale))
             }
             if let time = message.timestamp {
                 Text("·")
                 Text(time, style: .time)
-                    .scarfStyle(.caption)
+                    .font(ChatFontScale.caption(chatFontScale))
             }
             if let seconds = turnDuration {
                 Text("·")
                 Text(RichChatViewModel.formatTurnDuration(seconds))
-                    .font(ScarfFont.monoSmall)
+                    .font(ChatFontScale.monoSmall(chatFontScale))
                     .help("Wall-clock duration of this turn")
             }
         }
+        .font(ChatFontScale.caption(chatFontScale))
         .foregroundStyle(ScarfColor.foregroundFaint)
         .padding(.leading, 4)
     }