Code audit fix: BSDIFF overflow, Zip path traversal, process lifecycle, event system

[JusterZhu]

Code Audit — Critical/High Bug Fixes

Based on a full code audit of GeneralUpdate.Core and GeneralUpdate.Differential, this PR fixes ~25 bugs across the Core and Differential libraries.

🔴 Critical

Bug	File	Description
WriteInt64 overflow	BsdiffDiffer.cs:691	-long.MinValue overflows, corrupting BSDIFF sign-magnitude encoding
(int)control[0] truncation	BsdiffDiffer.cs:386,396,428	long > int.MaxValue silently truncated to negative — data loss on large patches
ReadFileWithBudget silent truncation	StreamingHdiffDiffer.cs:436-454	Files > 128MB silently truncated, producing incorrect patches
Zip decompress path traversal	ZipCompressionStrategy.cs:140-160	No validation — malicious ../../evil.exe entries can escape extraction dir
Overly broad StartsWith match	ZipCompressionStrategy.cs:51,85	"foo.dll" matches "foobar.dll" — wrong entries deleted in existing zip

🟠 High

Bug	File	Description
ProcessExit deadlock	ClientStrategy.cs:776	GetAwaiter().GetResult() in AppDomain.ProcessExit handler can deadlock with WPF/WinForms sync ctx
Strategy unconditional suicide	WindowsStrategy.cs, LinuxStrategy.cs, MacStrategy.cs	finally kills updater even when app launch failed — no recovery possible
Trace.Listeners global pollution	GeneralTracer.cs:158	Dispose() calls Trace.Listeners.Clear() — kills other libraries trace output
ProcessContract null check order	ProcessContract.cs:186-188	Directory.Exists(null) before null check — misleading error message
HubConnection dispose lifecycle	UpgradeHubService.cs:49-88	DisposeAsync doesnt null _connection — StartAsync after dispose throws NRE
ConfigurationMapper silent null	ConfigurationMapper.cs:80	null source returns empty config — caller unaware of misconfiguration
DefaultRetryPolicy status code match	DefaultRetryPolicy.cs:134-138	s.Contains("500") can match URL paths, not just status codes

🟡 Medium

Bug	File	Description
EventManager singleton not resettable	EventManager.cs	Added Reset() static method

Files Changed

• GeneralUpdate.Differential/Differ/BsdiffDiffer.cs
• GeneralUpdate.Differential/Differ/StreamingHdiffDiffer.cs
• GeneralUpdate.Core/Compress/ZipCompressionStrategy.cs
• GeneralUpdate.Core/Strategy/ClientStrategy.cs
• GeneralUpdate.Core/Strategy/WindowsStrategy.cs
• GeneralUpdate.Core/Strategy/LinuxStrategy.cs
• GeneralUpdate.Core/Strategy/MacStrategy.cs
• GeneralUpdate.Core/Tracer/GeneralTracer.cs
• GeneralUpdate.Core/Configuration/ProcessContract.cs
• GeneralUpdate.Core/Configuration/ConfigurationMapper.cs
• GeneralUpdate.Core/Hubs/UpgradeHubService.cs
• GeneralUpdate.Core/Download/Policy/DefaultRetryPolicy.cs
• GeneralUpdate.Core/Event/EventManager.cs