Test coverage: AddRangeFromSync failure dump (DumpFailedSync) path

[hahn-kev-bot]

Follow-up from the test-suite review (batches merged as #92–#96).

Gap

DataModel.AddRangeFromSync: on a DbUpdateException the catch block logs, writes last-failed-import.json (DumpFailedSync), and rethrows. Neither the dump-file side effect nor the rethrow is asserted anywhere.

harmony/src/SIL.Harmony/DataModel.cs

Lines 138 to 168 in 03f609f

	async Task ISyncable.AddRangeFromSync(IEnumerable<Commit> commits)
	{
	commits = commits.ToArray();
	try
	{
	await using var repo = await _crdtRepositoryFactory.CreateRepository();
	using var locked = await repo.Lock();
	repo.ClearChangeTracker();
	_timeProvider.TakeLatestTime(commits.Select(c => c.HybridDateTime));
	var (oldestChange, newCommits) = await repo.FilterExistingCommits(commits.ToArray());
	//no changes added
	if (oldestChange is null || newCommits is []) return;
	await using var transaction = await repo.BeginTransactionAsync();
	var updatedCommits = await repo.AddCommits(newCommits);
	await UpdateSnapshots(repo, updatedCommits);
	await ValidateCommits(repo);
	await transaction.CommitAsync();
	}
	catch (DbUpdateException e)
	{
	_logger.LogError(e, "Failed to sync commits, check {FailedImportPath} for more details", _crdtConfig.Value.FailedSyncOutputPath);
	await DumpFailedSync(new
	{
	ExceptionMessage = e.ToString(),
	Commits = commits.DefaultOrder(),
	Objects = e.Entries.Select(entry => entry.Entity)
	});
	throw;
	}
	}

harmony/src/SIL.Harmony/DataModel.cs

Lines 170 to 182 in 03f609f

	private async Task DumpFailedSync(object data)
	{
	try
	{
	Directory.CreateDirectory(_crdtConfig.Value.FailedSyncOutputPath);
	await using var failedImport =
	File.Create(Path.Combine(_crdtConfig.Value.FailedSyncOutputPath, "last-failed-import.json"));
	await JsonSerializer.SerializeAsync(failedImport, data, _serializerOptions);
	}
	catch (Exception e)
	{
	_logger.LogError(e, "Failed to dump failed import");
	}

Suggested test

• AddRangeFromSync_OnDbUpdateException_DumpsFailedImportAndRethrows

Why it matters

This is the sync failure-diagnostics contract — if it silently breaks, all sync debugging output is lost with no signal. The test needs a way to force a DbUpdateException during import (e.g. a conflicting/duplicate commit) and to point FailedSyncOutputPath at a temp directory.