Split IRegionEditContext into sub-capability interfaces

The core edit-context interface carried every specialized edit gesture, so
adding a field kind's ops meant a widening edit that forced every implementer
(base, in-memory, composed, preview, reversal, the test fake) to stub a new
method. Factor the specialized clusters out.

- Move the four StText paragraph-CRUD methods (TrySetParagraphText,
  TrySetParagraphStyle, TryInsertParagraph, TryDeleteParagraph) into a new
  optional IStructuredTextEditing interface. The one caller (FwStructuredTextField)
  queries `ctx as IStructuredTextEditing` and treats null as "unsupported" - the
  same rejection the core methods returned on a context with no StText rows. Only
  the composed context and the preview/test doubles implement it; the base and the
  in-memory/reversal contexts drop their stubs. Adding a future kind's ops is now a
  new sub-interface plus one implementer, not a shotgun edit across every context.

- Remove the five picture methods (TryInsertPicture, TryReplacePictureFile,
  TryDeletePicture, TrySetPictureMetadata, TryInsertPictureOrc). Picture editing
  was removed from the Avalonia region (the picture slice renders the Unsupported
  row), no caller invoked them, and the composed context did not override them -
  they were dead stubs in every implementer. Wrapping dead surface in an
  IPictureEditing that nothing implements or consumes would be empty ceremony, so
  the cluster is removed instead. RegionPictureMetadata (used by the
  picture-properties dialog) is unaffected.

Behavior-preserving: no gesture that succeeded before is rejected now.

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

Author: jasonleenaylor

Src/Common/FwAvalonia/FwAvaloniaTests/RegionEditingTests.cs

@@ -22,7 +22,7 @@
 namespace FwAvaloniaTests
 {
 	/// <summary>Records edit-context traffic so view editing behavior can be asserted without LCModel.</summary>
-	internal sealed class FakeRegionEditContext : IRegionEditContext
+	internal sealed class FakeRegionEditContext : IRegionEditContext, IStructuredTextEditing
 	{
 		public readonly List<(string Field, string Ws, string Value)> TextEdits = new List<(string, string, string)>();
 		public readonly List<(string Field, string Ws, RegionRichTextValue Value)> RichTextEdits
@@ -119,50 +119,6 @@ public bool TryDeleteParagraph(LexicalEditRegionField field, int paragraphIndex)
 			return ParagraphGestureResult;
 		}
 
-		// §19d: recorded picture traffic, so the picture field view can be asserted without LCModel.
-		public readonly List<(string Field, string SourceFile, RegionPictureMetadata Metadata)> PictureInserts
-			= new List<(string, string, RegionPictureMetadata)>();
-		public readonly List<(string Field, string SourceFile)> PictureReplaces = new List<(string, string)>();
-		public readonly List<string> PictureDeletes = new List<string>();
-		public readonly List<(string Field, RegionPictureMetadata Metadata)> PictureMetadataEdits
-			= new List<(string, RegionPictureMetadata)>();
-		public readonly List<(string Field, string Ws, int Caret, string SourceFile)> PictureOrcInserts
-			= new List<(string, string, int, string)>();
-
-		/// <summary>What the next picture gesture reports (false = rejected, e.g. a missing file).</summary>
-		public bool PictureGestureResult = true;
-
-		public bool TryInsertPicture(LexicalEditRegionField field, string sourceFile, RegionPictureMetadata metadata)
-		{
-			PictureInserts.Add((field.Field, sourceFile, metadata));
-			return PictureGestureResult;
-		}
-
-		public bool TryReplacePictureFile(LexicalEditRegionField field, string sourceFile)
-		{
-			PictureReplaces.Add((field.Field, sourceFile));
-			return PictureGestureResult;
-		}
-
-		public bool TryDeletePicture(LexicalEditRegionField field)
-		{
-			PictureDeletes.Add(field.Field);
-			return PictureGestureResult;
-		}
-
-		public bool TrySetPictureMetadata(LexicalEditRegionField field, RegionPictureMetadata metadata)
-		{
-			PictureMetadataEdits.Add((field.Field, metadata));
-			return PictureGestureResult;
-		}
-
-		public bool TryInsertPictureOrc(LexicalEditRegionField field, string ws, int caretPosition,
-			string sourceFile, RegionPictureMetadata metadata)
-		{
-			PictureOrcInserts.Add((field.Field, ws, caretPosition, sourceFile));
-			return PictureGestureResult;
-		}
-
 		public IReadOnlyList<string> Validate() => ValidateResult;
 
 		public void Commit()

Src/Common/FwAvalonia/Preview/LexicalEditPreviewSupport.cs

@@ -130,7 +130,7 @@ public LexicalEditPreviewScenario(LexicalEditRegionModel model, IRegionEditConte
 		public IRegionEditContext EditContext { get; }
 	}
 
-	internal sealed class PreviewRegionEditContext : IRegionEditContext
+	internal sealed class PreviewRegionEditContext : IRegionEditContext, IStructuredTextEditing
 	{
 		public bool IsOpen { get; private set; }
 
@@ -189,20 +189,6 @@ public bool TryDeleteParagraph(LexicalEditRegionField field, int paragraphIndex)
 			return true;
 		}
 
-		// §19d: the preview support context stages pictures/audio as "accepted" so the preview renders the
-		// affordances; the preview never touches real LCModel/files (it is the detached preview path).
-		public bool TryInsertPicture(LexicalEditRegionField field, string sourceFile, RegionPictureMetadata metadata)
-		{ IsOpen = true; return true; }
-		public bool TryReplacePictureFile(LexicalEditRegionField field, string sourceFile)
-		{ IsOpen = true; return true; }
-		public bool TryDeletePicture(LexicalEditRegionField field)
-		{ IsOpen = true; return true; }
-		public bool TrySetPictureMetadata(LexicalEditRegionField field, RegionPictureMetadata metadata)
-		{ IsOpen = true; return true; }
-		public bool TryInsertPictureOrc(LexicalEditRegionField field, string ws, int caretPosition,
-			string sourceFile, RegionPictureMetadata metadata)
-		{ IsOpen = true; return true; }
-
 		public IReadOnlyList<string> Validate()
 			=> Array.Empty<string>();
 

Src/Common/FwAvalonia/Region/FwStructuredTextField.cs

@@ -20,7 +20,7 @@ namespace SIL.FieldWorks.Common.FwAvalonia.Region
 	/// replacement for the legacy <c>StTextSlice</c> RootSite rich editor. A vertical stack of one
 	/// bordered, dense editor row per paragraph; each row carries a run-aware text editor (the SAME
 	/// staging the single-WS <see cref="FwMultiWsTextField"/> uses — TextChanged replays the untouched
-	/// runs around the edit and stages through <see cref="IRegionEditContext.TrySetParagraphText"/>),
+	/// runs around the edit and stages through <see cref="IStructuredTextEditing.TrySetParagraphText"/>),
 	/// a per-paragraph named-style picker (the shared <see cref="FwOptionPicker"/>), and add/delete
 	/// paragraph affordances. Enter at a paragraph's end inserts a paragraph after it; Backspace in an
 	/// empty paragraph (when more than one remains) deletes it.
@@ -53,11 +53,15 @@ public FwStructuredTextField(
 			AutomationProperties.SetAutomationId(this, automationId);
 			AutomationProperties.SetName(this, field.Label ?? field.Field ?? automationId);
 
+			// Paragraph CRUD is the optional IStructuredTextEditing capability; a context without it leaves
+			// the rows displayed but inert (each gesture below no-ops), the same rejection the former core
+			// IRegionEditContext paragraph methods returned on a context with no StText rows.
+			var structuredText = editContext as IStructuredTextEditing;
 			var editable = editContext != null && field.IsEditable;
 			var paragraphs = field.Paragraphs;
 			for (var i = 0; i < paragraphs.Count; i++)
 			{
-				Children.Add(BuildParagraphRow(field, automationId, editContext, writingSystemFocused,
+				Children.Add(BuildParagraphRow(field, automationId, structuredText, writingSystemFocused,
 					gestureCompleted, clipboard, paragraphs[i], i, paragraphs.Count, editable));
 			}
 
@@ -66,13 +70,13 @@ public FwStructuredTextField(
 			// — the first keystroke materializes the StText through the edit-context setter (index 0).
 			if (paragraphs.Count == 0)
 			{
-				Children.Add(BuildParagraphRow(field, automationId, editContext, writingSystemFocused,
+				Children.Add(BuildParagraphRow(field, automationId, structuredText, writingSystemFocused,
 					gestureCompleted, clipboard, new RegionParagraph(null), 0, 1, editable));
 			}
 		}
 
 		private Control BuildParagraphRow(
-			LexicalEditRegionField field, string automationId, IRegionEditContext editContext,
+			LexicalEditRegionField field, string automationId, IStructuredTextEditing editContext,
 			Action<string> writingSystemFocused, Action gestureCompleted, IFwClipboard clipboard,
 			RegionParagraph paragraph, int index, int paragraphCount, bool fieldEditable)
 		{
@@ -129,7 +133,7 @@ private Control BuildParagraphRow(
 				{
 					if (e.Key == Key.Enter)
 					{
-						if (editContext.TryInsertParagraph(field, index))
+						if (editContext != null && editContext.TryInsertParagraph(field, index))
 						{
 							gestureCompleted?.Invoke();
 							e.Handled = true;
@@ -142,7 +146,7 @@ private Control BuildParagraphRow(
 						&& box.CaretIndex == 0
 						&& paragraphCount > 1)
 					{
-						if (editContext.TryDeleteParagraph(field, index))
+						if (editContext != null && editContext.TryDeleteParagraph(field, index))
 						{
 							gestureCompleted?.Invoke();
 							e.Handled = true;
@@ -158,7 +162,7 @@ private Control BuildParagraphRow(
 				addAffordance = BuildIconButton(automationId + ".Para." + index + ".Add", "+",
 					FwAvaloniaStrings.AddParagraph, () =>
 					{
-						if (editContext.TryInsertParagraph(field, index))
+						if (editContext != null && editContext.TryInsertParagraph(field, index))
 							gestureCompleted?.Invoke();
 					});
 
@@ -169,7 +173,7 @@ private Control BuildParagraphRow(
 					deleteAffordance = BuildIconButton(automationId + ".Para." + index + ".Delete", "×",
 						FwAvaloniaStrings.DeleteParagraph, () =>
 						{
-							if (editContext.TryDeleteParagraph(field, index))
+							if (editContext != null && editContext.TryDeleteParagraph(field, index))
 								gestureCompleted?.Invoke();
 						});
 				}
@@ -241,7 +245,7 @@ private Control BuildParagraphRow(
 		// a TextChanged stages a plain-text-over-preserved-runs edit through the paragraph seam. A
 		// last-staged guard keeps the template's initial set and no-op events from staging; the guard
 		// advances only on a successful stage so a failed write re-attempts.
-		private void WireParagraphTextEditing(LexicalEditRegionField field, IRegionEditContext editContext,
+		private void WireParagraphTextEditing(LexicalEditRegionField field, IStructuredTextEditing editContext,
 			TextBox box, RegionRichTextValue currentRich, int index, Action<RegionRichTextValue> onStaged)
 		{
 			var lastStaged = currentRich?.PlainText ?? string.Empty;
@@ -253,7 +257,7 @@ private void WireParagraphTextEditing(LexicalEditRegionField field, IRegionEditC
 				var updatedRich = RegionRichTextEditAlgorithms.ApplyPlainTextEdit(
 					currentRich ?? RegionRichTextEditAlgorithms.FromRuns(string.Empty, Array.Empty<RegionTextRun>()),
 					text);
-				if (editContext.TrySetParagraphText(field, index, updatedRich))
+				if (editContext != null && editContext.TrySetParagraphText(field, index, updatedRich))
 				{
 					lastStaged = text;
 					currentRich = updatedRich;
@@ -270,7 +274,7 @@ private void WireParagraphTextEditing(LexicalEditRegionField field, IRegionEditC
 		// seam and completes the gesture (structural: commit immediately + re-show). Built only when the
 		// field carries available paragraph styles.
 		private Control BuildStyleAffordance(LexicalEditRegionField field, string automationId,
-			IRegionEditContext editContext, Action gestureCompleted, RegionParagraph paragraph, int index)
+			IStructuredTextEditing editContext, Action gestureCompleted, RegionParagraph paragraph, int index)
 		{
 			if (field.AvailableParagraphStyles == null || field.AvailableParagraphStyles.Count == 0)
 				return null;
@@ -312,7 +316,7 @@ private Control BuildStyleAffordance(LexicalEditRegionField field, string automa
 			{
 				styleFlyout.Hide();
 				var styleName = string.IsNullOrEmpty(option?.Key) ? null : option.Key;
-				if (editContext.TrySetParagraphStyle(field, index, styleName))
+				if (editContext != null && editContext.TrySetParagraphStyle(field, index, styleName))
 					gestureCompleted?.Invoke();
 			};
 			stylePicker.OptionCommitted += styleCommitted;
@@ -401,7 +405,7 @@ private Control BuildValueContentWithFontSwap(LexicalEditRegionField field, stri
 		// clear entry plus the project's character styles, acting on the box's current selection and
 		// staging ApplySpanNamedStyle through the paragraph-text seam. Null when no character styles.
 		private Control BuildCharStyleAffordance(LexicalEditRegionField field, string automationId,
-			IRegionEditContext editContext, Action gestureCompleted, TextBox box, int index,
+			IStructuredTextEditing editContext, Action gestureCompleted, TextBox box, int index,
 			Func<RegionRichTextValue> getRich, Action<RegionRichTextValue> setRich)
 		{
 			if (field.AvailableNamedStyles == null || field.AvailableNamedStyles.Count == 0)
@@ -449,7 +453,7 @@ private Control BuildCharStyleAffordance(LexicalEditRegionField field, string au
 					var styleName = string.IsNullOrEmpty(option?.Key) ? null : option.Key;
 					var restyled = RegionRichTextEditAlgorithms.ApplySpanNamedStyle(rich, lo, hi, styleName);
 					if (!ReferenceEquals(restyled, rich)
-						&& editContext.TrySetParagraphText(field, index, restyled))
+						&& editContext != null && editContext.TrySetParagraphText(field, index, restyled))
 					{
 						setRich(restyled);
 						gestureCompleted?.Invoke();
@@ -463,7 +467,7 @@ private Control BuildCharStyleAffordance(LexicalEditRegionField field, string au
 		// writing systems (no clear entry), acting on the box's current selection and staging
 		// RetagSpanWritingSystem through the paragraph-text seam. Null when no writing systems.
 		private Control BuildWsRetagAffordance(LexicalEditRegionField field, string automationId,
-			IRegionEditContext editContext, Action gestureCompleted, TextBox box, int index,
+			IStructuredTextEditing editContext, Action gestureCompleted, TextBox box, int index,
 			Func<RegionRichTextValue> getRich, Action<RegionRichTextValue> setRich)
 		{
 			if (field.AvailableWritingSystems == null || field.AvailableWritingSystems.Count == 0)
@@ -510,7 +514,7 @@ private Control BuildWsRetagAffordance(LexicalEditRegionField field, string auto
 						new[] { new RegionTextRun(box.Text ?? string.Empty) });
 					var retagged = RegionRichTextEditAlgorithms.RetagSpanWritingSystem(rich, lo, hi, option.Key);
 					if (!ReferenceEquals(retagged, rich)
-						&& editContext.TrySetParagraphText(field, index, retagged))
+						&& editContext != null && editContext.TrySetParagraphText(field, index, retagged))
 					{
 						setRich(retagged);
 						gestureCompleted?.Invoke();

Src/Common/FwAvalonia/Region/IRegionEditContext.cs

@@ -57,84 +57,6 @@ public interface IRegionEditContext : IEditSession
 		/// </summary>
 		bool TryRemoveReferenceItem(LexicalEditRegionField field, string optionKey);
 
-		/// <summary>
-		/// §19a: stages a run-aware text edit to ONE paragraph of a
-		/// <see cref="RegionFieldKind.StructuredText"/> (StText) field, opening the session on the first
-		/// edit. Returns false — WITHOUT opening the session — for a non-StText row, an out-of-range
-		/// paragraph index, or an ORC/lossy (read-only) paragraph. Like the run-aware single-WS path,
-		/// the rich payload preserves run metadata so the product <c>ITsString</c> rebuilds without
-		/// flattening.
-		/// </summary>
-		bool TrySetParagraphText(LexicalEditRegionField field, int paragraphIndex, RegionRichTextValue value);
-
-		/// <summary>
-		/// §19a: stages setting (or clearing, when <paramref name="styleName"/> is null/empty) the named
-		/// paragraph style of ONE paragraph of a <see cref="RegionFieldKind.StructuredText"/> field.
-		/// Returns false — without opening the session — for a non-StText row or an out-of-range index.
-		/// </summary>
-		bool TrySetParagraphStyle(LexicalEditRegionField field, int paragraphIndex, string styleName);
-
-		/// <summary>
-		/// §19a: stages inserting a new empty paragraph AFTER <paramref name="afterParagraphIndex"/> in a
-		/// <see cref="RegionFieldKind.StructuredText"/> field (a negative index inserts at the start).
-		/// Returns false — without opening the session — for a non-StText row. The structural gesture
-		/// commits immediately and the host re-shows (the model's paragraph list is a compose snapshot).
-		/// </summary>
-		bool TryInsertParagraph(LexicalEditRegionField field, int afterParagraphIndex);
-
-		/// <summary>
-		/// §19a: stages deleting paragraph <paramref name="paragraphIndex"/> of a
-		/// <see cref="RegionFieldKind.StructuredText"/> field. Returns false — without opening the
-		/// session — for a non-StText row, an out-of-range index, or when it would delete the only
-		/// paragraph (the StText always keeps at least one, like the legacy editor).
-		/// </summary>
-		bool TryDeleteParagraph(LexicalEditRegionField field, int paragraphIndex);
-
-		/// <summary>
-		/// §19d: inserts a NEW picture (an <c>ICmPicture</c>) into the picture-collection field
-		/// <paramref name="field"/> from the source image file <paramref name="sourceFile"/>, with the
-		/// supplied <paramref name="metadata"/> (caption/description/license/creator). The structural
-		/// gesture commits immediately and the host re-shows (the picture rows are a compose-time
-		/// snapshot). Returns false — WITHOUT opening the session — for a non-picture field, a missing
-		/// source file, or a field that does not accept pictures.
-		/// </summary>
-		bool TryInsertPicture(LexicalEditRegionField field, string sourceFile, RegionPictureMetadata metadata);
-
-		/// <summary>
-		/// §19d: replaces the image FILE of the existing picture <paramref name="field"/> represents
-		/// (a picture row carries one <c>ICmPicture</c>)
-		/// with <paramref name="sourceFile"/>, leaving its caption/metadata intact. Returns false —
-		/// without opening the session — for a non-picture row, an unresolvable picture, or a missing file.
-		/// </summary>
-		bool TryReplacePictureFile(LexicalEditRegionField field, string sourceFile);
-
-		/// <summary>
-		/// §19d: deletes the picture <paramref name="field"/> represents from its owning collection.
-		/// Returns false — without opening the session — for a non-picture row or an unresolvable picture.
-		/// </summary>
-		bool TryDeletePicture(LexicalEditRegionField field);
-
-		/// <summary>
-		/// §19d: updates the metadata (caption/description, and license/creator when the file metadata is
-		/// writable) of the picture <paramref name="field"/> represents. The caption/description are real
-		/// <c>ICmPicture</c> multistring properties (always written); license/creator are applied to the
-		/// image file's Palaso metadata only when the file is present/writable. Returns false — without
-		/// opening the session — for a non-picture row or an unresolvable picture.
-		/// </summary>
-		bool TrySetPictureMetadata(LexicalEditRegionField field, RegionPictureMetadata metadata);
-
-		/// <summary>
-		/// §19d (closes §19c's picture-ORC deferral): inserts a picture ORC into the rich-text VALUE of a
-		/// text field at <paramref name="caretPosition"/> — creates the <c>ICmPicture</c> from
-		/// <paramref name="sourceFile"/> (with <paramref name="metadata"/>) and inserts the
-		/// <c>kodtGuidMoveableObjDisp</c> run referencing it, like legacy
-		/// <c>FwEditingHelper.InsertPicture</c>. The gesture commits immediately and the host re-shows.
-		/// Returns false — without opening the session — for a field whose writing system cannot be
-		/// resolved, a missing source file, or a field that does not carry editable rich text.
-		/// </summary>
-		bool TryInsertPictureOrc(LexicalEditRegionField field, string ws, int caretPosition,
-			string sourceFile, RegionPictureMetadata metadata);
-
 		/// <summary>
 		/// Validates the staged state. Empty result means commit may proceed; messages are
 		/// user-facing (validation seam, deterministic order).