fix(ui): UiField wrapped-line cache coherent with the text at mouse-hit time

Fixes the crash the user hit twice today (captured in
artifacts/coldeve-acceptance-20260729/crash-hunt.log): clicking into a
multiline UiField - the examination window's inscription field - after
the text had changed since the last draw threw an unhandled
ArgumentOutOfRangeException from String.Substring and took the whole
client down (UiField.MeasureRange <- HitChar <- OnEvent MouseDown).

Root cause: _wrappedLines is a DRAW-side cache (rebuilt only in
DrawMultiLine) consumed by the INPUT side (HitChar on MouseDown and
drag-select MouseMove). Input events are pumped before the frame's
draw, so a mutation (backspace, SetText, paste) followed by a click in
the same pumped frame handed HitChar wrap lines describing the OLD,
longer text; measuring those stale ranges ran past the end of the live
string.

Fix: text mutations now bump a version (the _text field became a
private property so every existing mutation site participates without
churn), the draw records which version its wrap lines describe, and
HitChar proves coherence via EnsureWrappedLinesCurrent() - rebuilding
with the last draw width when stale. Rebuilding rather than clamping
keeps caret placement CORRECT against the live text, not merely
non-throwing. Two inversion-sensitive regression tests reproduce the
exact crash sequence (wrap long text, shrink without a draw, click);
they throw without the HitChar coherence call.

App tests 3,962 passed / 3 skipped (3,960 + 2 new).

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

tests/AcDream.App.Tests/UI/UiFieldTests.cs

@@ -70,6 +70,64 @@ public class UiFieldTests
         Assert.True(input.HistoryCount <= 100);
     }
 
+    [Fact]
+    public void MultilineClick_AfterTextShrankSinceLastWrap_DoesNotThrowAndPlacesCaretInNewText()
+    {
+        // The 2026-07-29 inscription-field crash: the wrapped-line cache is
+        // rebuilt at DRAW time, but mouse events are pumped BEFORE the
+        // frame's draw — a backspace/SetText followed by a click in the same
+        // frame handed HitChar wrap lines describing the OLD, longer text,
+        // and MeasureRange threw ArgumentOutOfRangeException from
+        // String.Substring. HitChar must prove wrap coherence itself.
+        var input = new UiField
+        {
+            OneLine = false,
+            Selectable = true,
+            Width = 120,
+            Height = 80,
+        };
+        input.SetText(
+            "a long inscription that wraps across multiple lines when it "
+            + "is measured with the fallback eight pixel glyph width");
+        // Simulate the draw-time cache build for the CURRENT (long) text.
+        input.EnsureWrappedLinesCurrent();
+
+        // Text shrinks with no draw in between — the cached lines now
+        // describe ranges far beyond the live string.
+        input.SetText("hi");
+
+        // Click low and to the right, where a stale line would demand a
+        // substring past the end of "hi". Pre-fix: throws. Post-fix: the
+        // cache rebuilds and the caret lands inside the new text.
+        var exception = Record.Exception(() => input.OnEvent(
+            new UiEvent(0u, input, UiEventType.MouseDown, Data1: 90, Data2: 60)));
+
+        Assert.Null(exception);
+        Assert.InRange(input.CaretPos, 0, input.Text.Length);
+    }
+
+    [Fact]
+    public void MultilineClick_AfterBackspacesSinceLastWrap_DoesNotThrow()
+    {
+        var input = new UiField
+        {
+            OneLine = false,
+            Selectable = true,
+            Width = 96,
+            Height = 60,
+        };
+        input.SetText("wrapped inscription text under edit right now");
+        input.EnsureWrappedLinesCurrent();
+        for (int i = 0; i < 30; i++)
+            input.Backspace();
+
+        var exception = Record.Exception(() => input.OnEvent(
+            new UiEvent(0u, input, UiEventType.MouseDown, Data1: 80, Data2: 40)));
+
+        Assert.Null(exception);
+        Assert.InRange(input.CaretPos, 0, input.Text.Length);
+    }
+
     [Fact]
     public void CharacterFilter_rejectsDisallowedInput()
     {