refactor: apply Single Responsibility Principle to Program.cs and ReplLoop.cs

extracted responsibilities from Program.cs (208→46 lines) and ReplLoop.cs (274→174 lines) into focused service classes: HeaderRenderer, SessionManager, ApplicationStartup, ResponseStreamer, SpinnerService, UsageDisplayer, and ContextCompactionService. Each class now has a single, well-defined responsibility, improving testability and maintainability.

ContextCompactionService.cs

@@ -0,0 +1,61 @@
+using Microsoft.Extensions.AI;
+using Spectre.Console;
+using AnchorCli.OpenRouter;
+
+namespace AnchorCli;
+
+/// <summary>
+/// Handles context compaction when the conversation approaches token limits.
+/// </summary>
+internal sealed class ContextCompactionService
+{
+    private readonly ContextCompactor _compactor;
+    private readonly List<ChatMessage> _history;
+    private readonly TokenTracker _tokenTracker;
+
+    public ContextCompactionService(
+        ContextCompactor compactor,
+        List<ChatMessage> history,
+        TokenTracker tokenTracker)
+    {
+        _compactor = compactor;
+        _history = history;
+        _tokenTracker = tokenTracker;
+    }
+
+    /// <summary>
+    /// Checks if compaction is needed and performs it if so.
+    /// Returns true if compaction was performed.
+    /// </summary>
+    public async Task<bool> TryCompactAsync()
+    {
+        if (!_tokenTracker.ShouldCompact())
+        {
+            return false;
+        }
+
+        var pct = _tokenTracker.ContextUsagePercent;
+        AnsiConsole.MarkupLine(
+            $"[yellow]⚠ Context at {pct:F0}% — compacting conversation history...[/]");
+
+        bool compacted = await AnsiConsole.Status()
+            .Spinner(Spinner.Known.BouncingBar)
+            .SpinnerStyle(Style.Parse("yellow"))
+            .StartAsync("Compacting context...", async ctx =>
+                await _compactor.TryCompactAsync(_history, default));
+
+        if (compacted)
+        {
+            AnsiConsole.MarkupLine(
+                $"[green]✓ Context compacted ({_history.Count} messages remaining)[/]");
+        }
+        else
+        {
+            AnsiConsole.MarkupLine(
+                "[dim grey]  (compaction skipped — not enough history to compress)[/]");
+        }
+
+        AnsiConsole.WriteLine();
+        return compacted;
+    }
+}