perf(draw): defer non-essential first-frame rendering (v1.4.9 R2)

Cut first-frame HITCH from ~127ms median down to ~76ms median (4-reload
sample, threshold lowered to 1ms for measurement) — comfortably under
Dalamud's 100ms warning threshold. ChatTwo upstream sits at ~63ms median
for comparison; the remaining ~13ms gap is the cost of HellionChat-only
features (Sidebar tab view, custom StatusBar, Honorific integration).

Mechanism: a single `_firstFrameDone` flag (flipped in Draw's finally
block) gates six sections that don't need to render on frame 0:

  - StatusBar.Draw (~12ms): the bottom status bar
  - DrawChannelName chunks (~17ms): SeString-Renderer layout, replaced
    with a plain-text fallback (activeTab.Name) for frame 0
  - PositionReset/BoundsCheck (~10ms): EnsureWindowOnScreen viewport
    iteration, only matters once the user notices a mispositioned window
  - DrawV061HintBannerIfNeeded (~3-5ms): v0.6.1 migration notice
  - DrawAutoComplete (~6ms): renders nothing until the user types a command
  - InputPreview.CalculatePreview (~3-5ms): triggers InputPreview first-
    frame lazy init, user-typing-driven anyway

Frame 1 then renders all of them in ~40ms (still well under the warning
threshold), and frames 2+ stay at 0ms as before. User sees the deferred
sections ~17ms (60fps) later than before — invisible inside the ~2.5s
Atlas-Build window after every plugin reload.

Hypothesis triage from the R2-profiling pass:
  - (a) Atlas-Sync-Fallback: falsified. xllog shows the Atlas-Complete
    line always lands ~2.5s before the HITCH frame.
  - (b) Theme-Apply ABGR-Cache-Init: not dominant. PushGlobal is 5ms.
  - (c) Multiple-Window-Render: falsified in v1.4.9 Stage-2-Lazy-Init
    diagnose (deferred 4 windows, no measurable delta).
  - (d) DrawList-Setup-Cost per Window: actual root cause. Layout cost
    distributes evenly across ~10 ImGui sections inside ChatLogWindow
    (5-20ms each). No single hot-spot to optimise — the six selective
    skips above are the pragmatic fix.

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

HellionChat/Ui/ChatLogWindow.cs

@@ -636,6 +636,15 @@ public sealed class ChatLogWindow : Window
         IsOpen = true;
     }
 
+    // v1.4.9 R2: defer non-essential rendering on the first Draw call so the
+    // plugin-load stays under Dalamud's 100ms HITCH warning threshold. First-
+    // frame ImGui layout cost on a populated ChatLog ~127ms — deferring six
+    // non-essential sections (StatusBar, ChannelName chunks, PositionReset/
+    // BoundsCheck, HintBanner, AutoComplete, InputPreview.CalculatePreview)
+    // shaves ~33ms down to ~94ms. User sees the deferred sections one frame
+    // (~17ms at 60fps) late, invisible inside the post-reload Atlas-Build.
+    private bool _firstFrameDone;
+
     public override void Draw()
     {
         DrewThisFrame = true;
@@ -643,7 +652,11 @@ public sealed class ChatLogWindow : Window
         {
             DrawChatLog();
             AddPopOutsToDraw();
-            DrawAutoComplete();
+
+            // v1.4.9 R2: AutoComplete renders nothing until the user starts
+            // typing a command — safe to skip on the first frame. ~6ms.
+            if (_firstFrameDone)
+                DrawAutoComplete();
         }
         catch (Exception ex)
         {
@@ -665,6 +678,13 @@ public sealed class ChatLogWindow : Window
             // input focus, which breaks every other ImGui window.
             Activate = false;
         }
+        finally
+        {
+            // Flag flips after the first Draw completes (success or caught
+            // exception). Sub-methods read it to decide whether to render
+            // non-essential UI sections.
+            _firstFrameDone = true;
+        }
     }
 
     private static bool IsChatMode =>
@@ -680,18 +700,25 @@ public sealed class ChatLogWindow : Window
         LastWindowSize = currentSize;
         LastWindowPos = ImGui.GetWindowPos();
 
-        // Manual reset snaps unconditionally; on-load check only fires when the
-        // stored position has no overlap with any visible viewport.
-        if (RequestPositionReset)
+        // v1.4.9 R2: skip the bounds-check chain on the first frame. The
+        // EnsureWindowOnScreen viewport iteration is ~10ms first-frame and
+        // not user-visible — frame 1 catches the same check before the
+        // user notices a mispositioned window.
+        if (_firstFrameDone)
         {
-            RequestPositionReset = false;
-            DidOnLoadBoundsCheck = true;
-            ApplySafeDefaultPosition("manual-reset");
-        }
-        else if (!DidOnLoadBoundsCheck)
-        {
-            DidOnLoadBoundsCheck = true;
-            EnsureWindowOnScreen("on-load");
+            // Manual reset snaps unconditionally; on-load check only fires when the
+            // stored position has no overlap with any visible viewport.
+            if (RequestPositionReset)
+            {
+                RequestPositionReset = false;
+                DidOnLoadBoundsCheck = true;
+                ApplySafeDefaultPosition("manual-reset");
+            }
+            else if (!DidOnLoadBoundsCheck)
+            {
+                DidOnLoadBoundsCheck = true;
+                EnsureWindowOnScreen("on-load");
+            }
         }
 
         if (resized)
@@ -700,12 +727,17 @@ public sealed class ChatLogWindow : Window
         LastViewport = ImGui.GetWindowViewport().Handle;
         WasDocked = ImGui.IsWindowDocked();
 
-        if (IsChatMode && Plugin.InputPreview.IsDrawable)
+        // v1.4.9 R2: CalculatePreview triggers InputPreview's first-frame
+        // lazy init (~3-5ms). User-typing-driven, safe to defer one frame.
+        if (_firstFrameDone && IsChatMode && Plugin.InputPreview.IsDrawable)
             Plugin.InputPreview.CalculatePreview();
 
         // Render the hint banner first so it sits above the tab area at full
         // window width. ImGui accounts for its height automatically.
-        DrawV061HintBannerIfNeeded();
+        // v1.4.9 R2: skip on first frame (~3-5ms layout cost). The banner
+        // is a v0.6.1 migration notice that returns the same result frame 1.
+        if (_firstFrameDone)
+            DrawV061HintBannerIfNeeded();
 
         if (Plugin.Config.SidebarTabView)
             DrawTabSidebar();
@@ -938,7 +970,11 @@ public sealed class ChatLogWindow : Window
 
         // v1.2.0 — Bottom-Status-Bar. Letzter Render-Step in DrawChatLog,
         // damit alle Zeilen-Operationen davor keine Layout-Sprünge auslösen.
-        Plugin.StatusBar.Draw(Plugin);
+        // v1.4.9 R2: skip on the first frame; ~12ms of first-frame layout
+        // cost. User sees the StatusBar 1 frame (~17ms at 60fps) later
+        // which is hidden inside the post-reload Atlas-Build window.
+        if (_firstFrameDone)
+            Plugin.StatusBar.Draw(Plugin);
     }
 
     internal Dictionary<string, InputChannel> GetValidChannels()
@@ -989,6 +1025,16 @@ public sealed class ChatLogWindow : Window
 
     private void DrawChannelName(Tab activeTab)
     {
+        // v1.4.9 R2: plain-text fallback on the first frame. ReadChannelName
+        // builds SeString chunks and DrawChunks runs SeString-Renderer layout
+        // — together ~18ms first-frame. Frame 1 renders the real chunks; the
+        // user sees the tab name for ~17ms during the post-reload window.
+        if (!_firstFrameDone)
+        {
+            ImGui.TextUnformatted(activeTab.Name);
+            return;
+        }
+
         var currentChannel = ReadChannelName(activeTab);
         if (!currentChannel.SequenceEqual(PreviousChannel))
             PreviousChannel = currentChannel;