feat: Show tool output in Activity inspector (#12)

Add tool result display to the Activity detail pane. When selecting a
tool call, the inspector now shows Arguments → Output → Assistant
Message, giving full visibility into what was requested, what came back,
and how the assistant interpreted it.

- Add fetchToolResult(callId:) query to HermesDataService
- Fetch tool result on entry selection in ActivityViewModel
- Display output in styled monospaced box in detail pane
- Render assistant message with MarkdownContentView

Closes #12

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scarf/scarf/Core/Services/HermesDataService.swift

@@ -157,6 +157,17 @@ actor HermesDataService {
         return messages
     }
 
+    func fetchToolResult(callId: String) -> String? {
+        guard let db else { return nil }
+        let sql = "SELECT content FROM messages WHERE role = 'tool' AND tool_call_id = ? LIMIT 1"
+        var stmt: OpaquePointer?
+        guard sqlite3_prepare_v2(db, sql, -1, &stmt, nil) == SQLITE_OK else { return nil }
+        defer { sqlite3_finalize(stmt) }
+        sqlite3_bind_text(stmt, 1, callId, -1, sqliteTransient)
+        guard sqlite3_step(stmt) == SQLITE_ROW else { return nil }
+        return columnText(stmt!, 0)
+    }
+
     func fetchRecentToolCalls(limit: Int = QueryDefaults.toolCallLimit) -> [HermesMessage] {
         guard let db else { return [] }
         let sql = """

scarf/scarf/Features/Activity/ViewModels/ActivityViewModel.swift

@@ -8,6 +8,7 @@ final class ActivityViewModel {
     var filterKind: ToolKind?
     var filterSessionId: String?
     var selectedEntry: ActivityEntry?
+    var toolResult: String?
     var sessionPreviews: [String: String] = [:]
     var isLoading = true
 
@@ -54,6 +55,15 @@ final class ActivityViewModel {
         isLoading = false
     }
 
+    func selectEntry(_ entry: ActivityEntry?) async {
+        selectedEntry = entry
+        if let entry {
+            toolResult = await dataService.fetchToolResult(callId: entry.id)
+        } else {
+            toolResult = nil
+        }
+    }
+
     func cleanup() async {
         await dataService.close()
     }

scarf/scarf/Features/Activity/Views/ActivityView.swift

@@ -57,11 +57,8 @@ struct ActivityView: View {
         List(selection: Binding(
             get: { viewModel.selectedEntry?.id },
             set: { id in
-                if let id {
-                    viewModel.selectedEntry = viewModel.filteredActivity.first(where: { $0.id == id })
-                } else {
-                    viewModel.selectedEntry = nil
-                }
+                let entry = id.flatMap { id in viewModel.filteredActivity.first(where: { $0.id == id }) }
+                Task { await viewModel.selectEntry(entry) }
             }
         )) {
             ForEach(viewModel.filteredActivity) { entry in
@@ -146,14 +143,32 @@ struct ActivityView: View {
                             .clipShape(RoundedRectangle(cornerRadius: 6))
                     }
 
+                    if let result = viewModel.toolResult, !result.isEmpty {
+                        VStack(alignment: .leading, spacing: 4) {
+                            Text("Output")
+                                .font(.caption.bold())
+                                .foregroundStyle(.secondary)
+                            Text(result)
+                                .font(.system(.caption, design: .monospaced))
+                                .textSelection(.enabled)
+                                .lineLimit(50)
+                                .padding(8)
+                                .frame(maxWidth: .infinity, alignment: .leading)
+                                .background(Color(.textBackgroundColor).opacity(0.5))
+                                .clipShape(RoundedRectangle(cornerRadius: 6))
+                                .overlay(
+                                    RoundedRectangle(cornerRadius: 6)
+                                        .strokeBorder(.quaternary, lineWidth: 1)
+                                )
+                        }
+                    }
+
                     if !entry.messageContent.isEmpty {
                         VStack(alignment: .leading, spacing: 4) {
                             Text("Assistant Message")
                                 .font(.caption.bold())
                                 .foregroundStyle(.secondary)
-                            Text(entry.messageContent)
-                                .font(.caption)
-                                .textSelection(.enabled)
+                            MarkdownContentView(content: entry.messageContent)
                                 .padding(8)
                                 .frame(maxWidth: .infinity, alignment: .leading)
                                 .background(.quaternary.opacity(0.5))