fix(chat): CH6a/b rework — grip media, retail window-id model, floaty fixture

Applies docs/research/2026-08-10-ch6ab-review-findings.md in full:

- BLOCKER 1: UiResizeGrip now carries its ElementInfo/resolve pair and
  draws its own authored DirectState media (a synthetic parameterless
  grip still draws nothing, preserving existing resize-drag tests).
  DatWidgetFactory.BuildResizeGrip threads resolve through. All seven
  live grips on the main chat window now resolve a non-zero sprite,
  restoring the visible borders/corners CH6a silently dropped.

- SHOULD-FIX 2: ChatWindowState gains BroadcastTargetWindow, a sentinel
  distinct from every real window id (0-4), fixing the bug where the
  main window's explicit-addressing branch coincided with the broadcast
  check (both were literal 0). SetFilter's main-window no-op is dropped
  — the main window's filter is now genuinely settable. ChatWindowController
  .Bind takes a ChatWindowState (the same canonical instance the floating
  windows already share) and GetTranscriptLines builds a real accept
  predicate instead of accept:null. Verified safe: ClientLocal (0x1A)
  never reaches ChatLog (AddText routes it to the SpewBox and returns),
  so nothing observable regresses.

- SHOULD-FIX 3: UiButton.SuppressSelfToggle stops the four chat-window
  indicator buttons (DAT property 0x0B=true, no retail click handler)
  from flipping their own Selected mirror on a stray click.

- SHOULD-FIX 4: generated and committed chat_floaty_2100005b.json from
  the real installed dats; added the permanent RetailLayoutFixtureGenerator
  entry. All three flagged FloatingChatWindowController assumptions
  (input field, title bar, close button) are confirmed correct against
  real data — no controller code changes needed. New finding: unlike the
  main window, ALL EIGHT floaty border/corner elements are live Type-9
  grips (the floaty's own title bar is its move handle), so a floaty
  window resizes from every edge and corner.

- SHOULD-FIX 5: register row AP-189 documents the shared-500-entry/
  200-line-tail vs retail's per-window 10,000-line scrollback depth gap.

- NITs 1-5: documented the filter-persistence-only-on-/saveautoui
  asymmetry and the reconnect-preserves-filters intent; corrected the
  research doc's modifier-mask mislabel and the "ONLY function" false
  superlative; moved WrapText off ChatWindowController onto
  ChatTranscriptRenderer, closing the circular dependency.

Full Release suite: 12,420 passed / 4 skipped / 0 failed (baseline
12,392/4/0 at 22020ef2; net +28 tests, zero regressions).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/AcDream.App.Tests/UI/Layout/FixtureLoader.cs

@@ -60,6 +60,25 @@ public static class FixtureLoader
     public static AcDream.App.UI.Layout.ElementInfo LoadChatInfos()
         => LoadInfos("chat_2100006f.json");
 
+    /// <summary>
+    /// Deserializes the committed <c>chat_floaty_2100005b.json</c> fixture
+    /// (retail's floating chat windows 1-4, LayoutDesc <c>0x2100005B</c> — CH6a/b
+    /// REJECT-review SHOULD-FIX 4) into a raw <see cref="ElementInfo"/> tree and
+    /// builds the <see cref="ImportedLayout"/> using a null-returning sprite
+    /// resolver and no dat font — sufficient for conformance checks on resolved
+    /// widget types.
+    /// </summary>
+    public static ImportedLayout LoadFloatyChat()
+        => LayoutImporter.Build(LoadFloatyChatInfos(), _ => (0u, 0, 0), null);
+
+    /// <summary>
+    /// Deserializes the committed <c>chat_floaty_2100005b.json</c> fixture into
+    /// a raw <see cref="ElementInfo"/> tree WITHOUT calling
+    /// <see cref="LayoutImporter.Build"/>.
+    /// </summary>
+    public static AcDream.App.UI.Layout.ElementInfo LoadFloatyChatInfos()
+        => LoadInfos("chat_floaty_2100005b.json");
+
     /// <summary>Builds the committed retail radar LayoutDesc 0x21000074 fixture.</summary>
     public static ImportedLayout LoadRadar()
         => LayoutImporter.Build(LoadRadarInfos(), _ => (0u, 0, 0), null);