srtm: fix for old cached srtm files

[meee1]

No description provided.

[Copilot]

Pull request overview

Adds a cleanup step for cached SRTM files to address issues with older/invalid cache entries.

Changes:

• Deletes zero-length cached files in the SRTM data directory during static initialization.
• Purges cached files older than a fixed cutoff date to mitigate the “srtm3 bug cache” issue referenced in the linked discussion.

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[Copilot]

This runs in a static constructor; any IOException/UnauthorizedAccessException (e.g., directory missing, file locked, permissions) will bubble up as a TypeInitializationException and can break any feature that touches this type. Wrap the enumeration and per-file delete in a try/catch (ideally per file), and log failures rather than letting initialization fail.

Suggested change

	Directory.GetFiles(datadirectory).ToList().ForEach(x =>
	{
	var fi = new FileInfo(x);
	if (fi.Length == 0)
	File.Delete(x);
	// fix srtm3 bug cache - delete old files https://discuss.ardupilot.org/t/serious-terrain-data-error-and-how-to-fix-your-vehicle/142593
	if (fi.LastWriteTimeUtc < new DateTime(2026,03,01,0,0,0, DateTimeKind.Utc))
	File.Delete(x);
	});
	try
	{
	if (!Directory.Exists(datadirectory))
	{
	log.Warn($"SRTM data directory does not exist: '{datadirectory}'");
	return;
	}
	Directory.GetFiles(datadirectory).ToList().ForEach(x =>
	{
	try
	{
	var fi = new FileInfo(x);
	if (fi.Length == 0)
	File.Delete(x);
	// fix srtm3 bug cache - delete old files https://discuss.ardupilot.org/t/serious-terrain-data-error-and-how-to-fix-your-vehicle/142593
	if (fi.LastWriteTimeUtc < new DateTime(2026, 03, 01, 0, 0, 0, DateTimeKind.Utc))
	File.Delete(x);
	}
	catch (IOException ex)
	{
	log.Warn($"Failed to process SRTM file '{x}'", ex);
	}
	catch (UnauthorizedAccessException ex)
	{
	log.Warn($"Access denied processing SRTM file '{x}'", ex);
	}
	});
	}
	catch (IOException ex)
	{
	log.Warn($"Failed to enumerate SRTM data directory '{datadirectory}'", ex);
	}
	catch (UnauthorizedAccessException ex)
	{
	log.Warn($"Access denied enumerating SRTM data directory '{datadirectory}'", ex);
	}

[Copilot]

Using ToList().ForEach() for side effects forces an unnecessary list allocation and is harder to debug/step through. Prefer a simple foreach loop over Directory.GetFiles(datadirectory) to avoid the allocation and improve readability.

[Copilot]

The cleanup deletes all files in datadirectory that are older than the cutoff date, regardless of filename/extension. If that directory can contain anything besides SRTM cache files, this risks deleting unrelated files. Consider filtering by known cache filename pattern/extension (or checking expected prefixes) before applying the size/date deletion rules.

Suggested change

	if (fi.LastWriteTimeUtc < new DateTime(2026,03,01,0,0,0, DateTimeKind.Utc))
	if (fi.Extension.Equals(".hgt", StringComparison.OrdinalIgnoreCase) &&
	fi.LastWriteTimeUtc < new DateTime(2026,03,01,0,0,0, DateTimeKind.Utc))