LT-22625 Phase-1 base: Avalonia migration spine (UIMode defaults Legacy)

[johnml1135]

Phase-1 base: Avalonia migration spine

https://jira.sil.org/browse/LT-22625

First of a 4-PR stack landing Phase 1 of the WinForms→Avalonia migration. It introduces the seam that lets FieldWorks host either the legacy WinForms editing surface or the new Avalonia one, gated entirely on a UIMode setting that defaults to Legacy. At that default every call site added here resolves to its original, unchanged WinForms path; the Avalonia surface activates only when a user explicitly opts in via Tools → Options.

What this PR contains

• The Avalonia migration framework: region/composer (FullEntryRegionComposer), view-definition IR, owned controls, framework-neutral seam contracts, and the plugin registry.
• The base detail-editor surfaces active under UIMode=New: lexiconEdit, lexiconEditPopup, notebookEdit, posEdit.
• ~26 dialog-launcher call sites (Insert/Merge/Go To Entry, MSA and grammatical-info choosers, LexReference launchers, Interlinear's Add Allomorph/Add New Sense, and the three Options-dialog launch sites) each gated by the shared FwUtils.UIModeGates.ShouldUseAvaloniaUI(uiMode) predicate.
• FwAvalonia/FwAvaloniaDialogs infrastructure and the landed openspec change specs, plus the migration skills.
• A Stage-3 Avalonia browse mirror, shipped but currently inert. RecordBrowseView/BrowseViewer gained a full table overlay for list/browse tools — Configure Columns, Filter For/Restrict Date/Choose List flyouts, and a complete IBulkEditBarHost (bulk edit/copy/clear, Delete Rows, replace) — sitting on a large additive BrowseViewer API (IBrowseColumnSource + ~20 new methods). It activates per-tool through LexicalEditSurfaceResolver.SupportedAvaloniaBrowseToolNames, which is empty in this PR, so every browse/list tool falls back to the legacy BrowseViewer regardless of UIMode — asserted by InertFollowUpSurfacesFallBackToLegacy_BrowseTable. phase1-followup-table (see Stack) activates it one tool at a time.

How Legacy stays safe

• Fail-closed gate. ShouldUseAvaloniaUI returns true only for an ordinal-ignore-case "New"; null, empty, whitespace, or any other value → Legacy. Every one of the ~26 gate sites uses this single predicate.
• Loader isolation. The gate lives in FwUtils, which references no Avalonia type, and every gated branch that touches an Avalonia launcher is extracted into a [MethodImpl(NoInlining)] helper. Legacy execution therefore never resolves an Avalonia type unless a gate actually passes. Startup localization method-lookup has its own try/catch, so a missing/corrupt FwAvalonia.dll costs only the Avalonia dynamic strings, never the Chorus/Palaso localization managers.
• Legacy else-branches unchanged. Every legacy branch of every gated site is byte-equivalent to main (including the LexReferenceMultiSlice restructure, traced case-by-case); the settings migration path is untouched; no static-init or reflection route reaches the new launchers ungated.
• One shared (non-gated) site touched, but inert under Legacy. DTMenuHandler.OnDisplayDataTreeInsert's enablement check gained || m_dataEntryForm.IsExternalCommandAdapter. DataTree.IsExternalCommandAdapter defaults to false and is set true only by New-mode's hidden command-routing adapter (RecordEditView.Avalonia.cs, tasks 13.4/15.4), which exists purely to keep a legacy DataTree alive for right-click menu routing while the Avalonia surface is on screen. Legacy never sets it, so the added clause never fires there — the check evaluates identically to main — but it's a textual change to shared code outside the ~26 gate sites, so it's called out here rather than left implicit.
• BrowseViewer's one existing-method touch is additive-only. InstallNewColumns gained one line, m_avaloniaColumnFinders = null;, invalidating a cache field that only the (currently unreachable — see the Stage-3 browse mirror above) new methods ever read. Everything else BrowseViewer gained is new members bolted onto the class; no other existing method body changed.
• TsStringWrapper widened from internal to public, plus an additive FromXml factory/Xml property, so the cross-framework clipboard bridge (FwTsStringClipboard, task 3.13) can carry rich-text XML between the WinForms and Avalonia clipboard paths. No existing member's behavior changed.

Legacy-visible changes (things existing users see even at the default)

The gate keeps behavior on Legacy identical, but this PR does make a few changes visible to all users, called out here so review isn't surprised:

• New Options control. A "Lexical Edit UI" mode chooser appears on Tools → Options → Interface, in both the WinForms (LexOptionsDlg) and Avalonia (OptionsDialogView) dialogs, each carrying a "Beta: the New mode is incomplete" note.
• Two new settings. UIMode (default Legacy) and UIModeDisabledTools (default empty — a per-tool opt-out list read only after New mode is active).
• Filter-bar accessibility identity. Legacy browse filter-bar combos now expose per-column Name/AccessibleName values instead of a uniform "FwComboBox" literal — an intentional screen-reader improvement, pinned by a WinForms UIA test.
• Avalonia now ships with every install. FieldWorks/xWorks/LexTextControls reference FwAvalonia/FwAvaloniaDialogs, so the Avalonia binary stack deploys with every build and FwAvalonia.dll loads on core paths (behind Func indirection + the NoInlining gates). "Legacy installs don't need Avalonia" is no longer true.

New-mode parity deferrals

The New-mode (opt-in) path is narrower than the legacy dialogs it replaces in ~8 places, each marked // PARITY in-code (e.g. allomorph type-mismatch warning, link-allomorph/MSA first-item pickers, Insert Entry duplicate search not matching gloss, MGA catalog import unported). Legacy is unaffected. LcmChooserDialogLauncher ships with no production caller (private ctor, unreachable by design) — it is tested staging infrastructure for the future ReallySimpleListChooser migration (~54 sites), documented as STAGING in its doc comment.

Split out for separate assessment

A shared layout part (LexSense-Detail-Pictures) would make sense pictures appear in the legacy Lexicon Edit pane (they have been silently omitted there for over a decade). It is a plausible legacy bug-fix but an ungated, legacy-visible behavior change, so it is not in this PR — it is proposed separately so the team can decide on it independently.

Stack (each merges into the one above)

1. this → main
2. phase1-followup-interlinear → phase1-base
3. phase1-followup-rule → phase1-followup-interlinear
4. phase1-followup-table → phase1-followup-rule

Verification

Whole-solution build green; full CI-equivalent test run passes (7/7 CI checks). All ~26 gate sites verified fail-closed; every legacy else-branch verified equivalent to main; TonePars/XAmpleParser are byte-identical to main (this PR does not touch ParserCore/pcpatrflex). Draft until the stack is reviewed top-to-bottom.

---

This change is

[github-actions]

NUnit Tests

    1 files  ±    0      1 suites  ±0   11m 44s ⏱️ + 1m 8s
5 776 tests +1 474  5 695 ✅ +1 466  81 💤 +8  0 ❌ ±0 
5 785 runs  +1 474  5 704 ✅ +1 466  81 💤 +8  0 ❌ ±0 

Results for commit f409b5a. ± Comparison against base commit 84a4850.

♻️ This comment has been updated with latest results.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 65.11628% with 210 lines in your changes missing coverage. Please review.
✅ Project coverage is 36.42%. Comparing base (84a4850) to head (f409b5a).
⚠️ Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
Src/Common/FwAvalonia/AvaloniaDialogHost.cs	54.54%	34 Missing and 16 partials ⚠️
Src/Common/FwAvalonia/AvaloniaRegionHostControl.cs	48.80%	33 Missing and 10 partials ⚠️
...Controls/DetailControls/MorphTypeAtomicLauncher.cs	56.94%	19 Missing and 12 partials ⚠️
Src/Common/Controls/XMLViews/FilterBar.cs	40.47%	16 Missing and 9 partials ⚠️
Src/Common/FwAvalonia/CompositeDisposable.cs	31.03%	15 Missing and 5 partials ⚠️
Src/Common/FwAvalonia/FwAvaloniaPlatform.cs	61.53%	7 Missing and 8 partials ⚠️
Src/Common/FwAvalonia/FilterableDropdownSupport.cs	83.33%	2 Missing and 9 partials ⚠️
Src/Common/FieldWorks/WelcomeToFieldWorksDlg.cs	0.00%	7 Missing and 1 partial ⚠️
Src/Common/FwAvalonia/FwAvaloniaApp.cs	50.00%	3 Missing ⚠️
Src/Common/FwAvalonia/FwAvaloniaRuntime.cs	80.00%	1 Missing and 2 partials ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #964      +/-   ##
==========================================
+ Coverage   32.99%   36.42%   +3.43%     
==========================================
  Files        1202     1360     +158     
  Lines      278168   296299   +18131     
  Branches    37151    40316    +3165     
==========================================
+ Hits        91781   107930   +16149     
- Misses     158537   159018     +481     
- Partials    27850    29351    +1501     

Files with missing lines	Coverage Δ
Src/Common/Controls/DetailControls/DataTree.cs	43.73% <ø> (+6.18%)	⬆️
Src/Common/FieldWorks/FieldWorks.cs	0.73% <ø> (ø)
Src/Common/Framework/MainWindowDelegate.cs	2.40% <ø> (ø)
Src/Common/FwAvalonia/CompactDialogStyles.cs	100.00% <100.00%> (ø)
Src/Common/FwAvalonia/FwAvaloniaDensity.cs	100.00% <100.00%> (ø)
Src/Common/FwAvalonia/FwCheckBoxStyle.cs	100.00% <ø> (ø)
Src/Common/FwAvalonia/FwPosChooser.cs	87.82% <ø> (ø)
Src/Common/FwAvalonia/FwRadioButtonStyle.cs	100.00% <ø> (ø)
Src/Common/FwAvalonia/FwSurfaceStyles.cs	94.28% <ø> (ø)
.../Common/FwAvalonia/InputKeyClaimingAvaloniaHost.cs	41.17% <ø> (ø)
... and 128 more

... and 145 files with indirect coverage changes

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[github-actions]

⚠️ Commit Message Format Issues ⚠️
commit 973a98a090:
1: T1 Title exceeds max length (78>72): "Rename the composer, edit contexts, and slice plugins to the Detail vocabulary"

commit 8d21d03385:
3: B1 Line exceeds max length (456>80): "Reviewer chose the bare legacy stem over the qualified RegionSliceFactory, making the FwAvalonia.Region type a deliberate cross-namespace twin of DetailControls.SliceFactory; no CS0104 alias was needed (no site references the bare stem while importing DetailControls), and the engine-isolation audit's source denylist drops SliceFactory since FwAvalonia.Region now owns the twin while the assembly-level guard still enforces isolation; behavior-preserving."

commit ac50ecc427:
13: B1 Line exceeds max length (86>80): " LexiconFirstSliceEditContextEdgeCaseTests, RegionEditContextEditingTests,"
14: B1 Line exceeds max length (81>80): " RegionEditSessionLifecycleTests, StructuredText{Adapter,Integration,"
24: B1 Line exceeds max length (82>80): " RegionContextMenuCompositionTests, RegionObjectCommandExecutionTests,"

commit 896e92dc58:
4: B1 Line exceeds max length (81>80): "the project root into a flat Avalonia/ folder, so the Avalonia launchers/adapters"

commit 5f56b0b794:
6: B1 Line exceeds max length (88>80): " InsertEntryDialog* -> InsertEntryDlg* (InsertEntryPayload -> InsertEntryDlgPayload)"
7: B1 Line exceeds max length (89>80): " AddNewSenseDialog* -> AddNewSenseDlg* (AddNewSensePayload -> AddNewSenseDlgPayload)"
8: B1 Line exceeds max length (88>80): " MsaCreatorDialog* -> MsaCreatorDlg* (MsaCreatorPayload -> MsaCreatorDlgPayload)"
9: B1 Line exceeds max length (86>80): " OptionsDialog* -> LexOptionsDlg* (OptionsState -> LexOptionsDlgState)"

commit d82088fe43:
1: T1 Title exceeds max length (74>72): "Audit PR comments: strip migration framing, doc markers, and absence notes"

commit f409b5aad6:
25: B1 Line exceeds max length (83>80): "still backs AttachedHandlerCount for the recycling assertions. Behavior-preserving."

commit d200a34016:
13: B1 Line exceeds max length (81>80): " ComposedRegionEditContext looks up the one handler and calls the relevant slot,"
14: B1 Line exceeds max length (82>80): " rejecting an unsupported gesture by finding a null slot - the same rejection the"
18: B1 Line exceeds max length (81>80): "- Decompose the two long walkers by concern (pure mechanical extraction, no logic"
21: B1 Line exceeds max length (81>80): " ResolveTextRowWritingSystems / BuildTextRowValues / RegisterTextRowEditHandler;"
25: B1 Line exceeds max length (81>80): "Behavior-preserving: staging, undo labels, and rejection semantics are unchanged."

commit de9fe70e99:
10: B1 Line exceeds max length (83>80): " optional IStructuredTextEditing interface. The one caller (FwStructuredTextField)"
12: B1 Line exceeds max length (81>80): " same rejection the core methods returned on a context with no StText rows. Only"
13: B1 Line exceeds max length (82>80): " the composed context and the preview/test doubles implement it; the base and the"
14: B1 Line exceeds max length (83>80): " in-memory/reversal contexts drop their stubs. Adding a future kind's ops is now a"
15: B1 Line exceeds max length (82>80): " new sub-interface plus one implementer, not a shotgun edit across every context."
19: B1 Line exceeds max length (81>80): " was removed from the Avalonia region (the picture slice renders the Unsupported"
22: B1 Line exceeds max length (81>80): " IPictureEditing that nothing implements or consumes would be empty ceremony, so"

commit 45a569a188:
18: B1 Line exceeds max length (81>80): "the create-feature / add-value event docs and class doc for the present contract."

commit 88d4a587c8:
36: B1 Line exceeds max length (81>80): "(EntryDlgListener) uses the persistProvider overload, which never shows it. Those"
40: B1 Line exceeds max length (81>80): "(only the visible marker is added), the configurable multi-column matching browse"

commit df74847c7c:
1: T1 Title exceeds max length (74>72): "Trim the lexical-edit region to string, list-choice, and one native plugin"
6: B1 Line exceeds max length (85>80): "Kept: the string editors (FwMultiWsTextField single/multi-WS, FwStructuredTextField),"
7: B1 Line exceeds max length (88>80): "the list-choice editors (FwChooserField, FwReferenceVectorField including the composer's"
9: B1 Line exceeds max length (88>80): "LexReferenceMultiSlice), the structural Header / Literal / Unsupported rows, and the one"
10: B1 Line exceeds max length (88>80): "IRegionEditorPlugin contract with ReversalIndexEntryPlugin as the sole native-conversion"
13: B1 Line exceeds max length (90>80): "Deleted: the RegionFieldKind values Boolean/Date/EnumCombo/Integer/Image/Command and their"
14: B1 Line exceeds max length (88>80): "factory build methods; the FwGenDateField editor; the picture path (RegionPictureEditor,"
15: B1 Line exceeds max length (90>80): "LcmRegionMediaServices, the IRegionMediaServices media seam, the RegionFieldControlFactory"
18: B1 Line exceeds max length (86>80): "WinFormsLegacyDialogLauncher / RegionEditorServices); and the WinForms companion strip"
19: B1 Line exceeds max length (92>80): "(AvaloniaCompanionSlices, ComposedCustomEditorField, ComposedEntryRegion.CustomEditorFields,"
21: B1 Line exceeds max length (86>80): "RegionPictureDialogResult are retained (relocated into LexicalEditRegionModel) for the"
24: B1 Line exceeds max length (93>80): "All dropped editors now render the labeled Unsupported worklist row (never silently omitted):"
25: B1 Line exceeds max length (86>80): "the dropped scalar kinds fall through the composer's field dispatch to the Unsupported"
26: B1 Line exceeds max length (89>80): "fallback, and an unclaimed editor="Custom" slice (other than the reference-vector routes)"
27: B1 Line exceeds max length (93>80): "resolves plugin registry -> Unsupported. The Unsupported row now carries its object and slice"
30: B1 Line exceeds max length (82>80): "FwMultiWsTextField lost its media dependency: the mediaServices ctor param and the"
31: B1 Line exceeds max length (93>80): "audio play/record row are gone; a voice/audio writing-system alternative renders as read-only"
32: B1 Line exceeds max length (96>80): "text (no in-pane player). The WS font/RTL/keyboard, the per-run rich-text seam (TrySetRichText),"
33: B1 Line exceeds max length (82>80): "the Character Style / WS retag / Insert Link / Delete Object context menu, and the"
36: B1 Line exceeds max length (91>80): "Tests: the burn-down census is rewritten to assert builtins == { ReversalIndexEntrySlice },"
37: B1 Line exceeds max length (90>80): "that the reference-vector classes are composer-absorbed (not plugin-claimed), and that the"
38: B1 Line exceeds max length (95>80): "formerly launcher-routed slices plus the Chorus notes bar are unclaimed; a composer test proves"
39: B1 Line exceeds max length (94>80): "an unclaimed custom slice composes as Unsupported and a plugin claim composes as a Custom row."
40: B1 Line exceeds max length (96>80): "Tests of deleted code were removed; factory/compose/visual tests were updated so dropped editors"
43: B1 Line exceeds max length (93>80): "Docs updated to the forward conversion path: the winforms-free-lexeme-editor decision doc and"
44: B1 Line exceeds max length (96>80): "native-views-audit describe the one plugin contract with the single native exemplar, no launcher"
45: B1 Line exceeds max length (98>80): "stopgap, no companion strip, and Unsupported rows as the burn-down worklist; the migration skill's"
46: B1 Line exceeds max length (92>80): "plugin-registry section and control-exemplar map are trimmed to the same shape with a worked"
47: B1 Line exceeds max length (89>80): ""convert a custom slice to a native editor" example anchored on ReversalIndexEntryPlugin."

commit ca58e388f6:
1: T1 Title exceeds max length (76>72): "Host the POS-chooser and option-picker dropdowns in flyouts, not free popups"

commit 32c925b51c:
1: T1 Title exceeds max length (82>72): "Fix Shift+Arrow selection in the multi-WS field; pin selection with headless tests"

commit de52e69131:
13: B1 Line exceeds max length (82>80): "multistring signal is carried on the row (LexicalEditRegionField.IsMultiStringRow,"
22: B1 Line exceeds max length (81>80): "single-string row yields the field menu plus mnuDataTree-Object, and that the two"

commit 02e14541af:
20: B1 Line exceeds max length (82>80): "inline affordances; the per-run font-swap display and the audio row are untouched."
23: B1 Line exceeds max length (83>80): "host menu as its single right-click surface (it owns the field's Swap/Convert-style"
24: B1 Line exceeds max length (81>80): "commands and Avalonia items cannot be merged into it), so the relocated rich-text"
33: B1 Line exceeds max length (81>80): "browse/in-cell path (showWritingSystemAbbreviation == false) still suppresses the"
37: B1 Line exceeds max length (81>80): "Tests: the FwAvaloniaTests that asserted the inline affordance buttons now assert"
41: B1 Line exceeds max length (81>80): "Added coverage that a text row draws no inline affordance buttons (the operations"