[kornman00]

Summary

• Make each CodeEditor own one AvalonEdit SearchPanel instead of installing
  additional panels during load and document changes.
• Add dual-target characterization for the existing AvalonEdit 6.0.0 editor
  behavior and packaged public contracts.
• Upgrade AvalonEdit to 6.3.1.120 while preserving the characterized behavior
  on net48 and net10.0-windows.

Review guide

The commits are intentionally separated:

1. e773302 Own one CodeEditor search panel
   • fixes the duplicated search-handler ownership;
   • adds focused STA/WPF regression coverage.
2. cfefb87 Characterize AvalonEdit 6.0.0 contracts
   • captures settings, highlighting, document replacement, and undo/redo
     behavior before the dependency change;
   • extends package validation to compile and run an external CodeEditor
     consumer;
   • keys compatibility restores by the complete package family so a
     same-version stale package cannot be reused.
3. 28e1cb1 Upgrade AvalonEdit to 6.3.1.120
   • changes only the dependency version, selected package assets, and expected
     assembly identity.

The characterization remained green after the upgrade, so no compatibility-fix
commit was required.

SearchPanel ownership

SearchPanel.Install creates a new panel and input handler each time it is
called. CodeEditor previously called it from both Loaded and
DocumentChanged, allowing handlers and panels to accumulate.

The editor now installs one privately owned panel during construction.
AvalonEdit's panel already follows TextArea.DocumentChanged, so the same panel
continues to search the current document without Gemini reinstalling it.

The regression tests cover:

• repeated load/unload cycles and document replacement;
• one effective search handler and one visual panel;
• Find, next/previous, close, case, whole-word, regex, and invalid-regex
  behavior;
• old-document and owned-subscription lifetimes.

AvalonEdit package contract

The package-only compatibility host now consumes
Gemini.Modules.CodeEditor and compiles external implementations against the
public AvalonEdit types exposed by CodeEditor, ICodeEditorView, and
ILanguageDefinition.

Resolved assets after the upgrade:

• net48: lib/net462/ICSharpCode.AvalonEdit.dll
• net10.0-windows: lib/net8.0-windows7.0/ICSharpCode.AvalonEdit.dll

Both hosts load assembly version 6.3.1.120.

AvalonEdit is strong-named, and its assembly version changes from 6.0.0.0 to
6.3.1.120. Extensions that use the exposed AvalonEdit types must rebuild
against the updated package family. This change does not add binding redirects
or promise binary compatibility for assemblies already compiled against
AvalonEdit 6.0.0.

Validation

dotnet restore src\Gemini.sln --configfile src\NuGet.config
dotnet build src\Gemini.sln --configuration Release --no-restore
dotnet test --project src\Gemini.Tests\Gemini.Tests.csproj --configuration Release --framework net48 --no-build --no-restore
dotnet test --project src\Gemini.Tests\Gemini.Tests.csproj --configuration Release --framework net10.0-windows --no-build --no-restore
dotnet pack src\Gemini.sln --configuration Release --no-build --no-restore --output build\packages
.\eng\validate-artifacts.ps1

Results:

• Release build: 0 warnings, 0 errors.
• Tests: 143 passed on net48; 143 passed on net10.0-windows.
• Eight primary packages and their symbol packages validated.
• Exact framework-specific AvalonEdit assets validated.
• Package-only external consumers passed on both retained targets.
• Gemini.Demo smoke checks passed for supported C# editing, highlighting,
  search navigation/options, document switching, and editor close/reopen
  cycles on both targets.

Base and rollback

• Based on tgjones/gemini@6994950fe49f4b7d344e673b2590441043730175.
• The search ownership fix is independent of the dependency upgrade.
• Reverting 28e1cb1 returns to the characterized AvalonEdit 6.0.0 contract
  without reverting the search ownership fix or its tests.
• Package publication remains handled by the existing upstream workflow.