Fix dangling stack references in ParseGuid and subscription parsing

[ritchiecarroll]

Summary

Fixes two uses of stack memory after its lifetime ended (undefined behavior). Both are one-line changes.

ParseGuid(const uint8_t* data, bool swapEndianness) — src/lib/Convert.cpp

swappedBytes[16] was declared inside the if (swapEndianness) block, encodedBytes was pointed at it, and the bytes were read through encodedBytes after the block had ended. With g++ 10.5 at -O2 the swapped bytes are never stored, so every .NET-ordered Guid decodes as garbage; unoptimized builds happen to work. The array is now declared at function scope.

No code in this repository calls ParseGuid with swapEndianness = true, so this only affects consumers of the public API. It was found in a port of this code (snapdb/cppapi), where Release builds decoded every Guid incorrectly.

SubscriberConnection::ParseSubscriptionRequest — src/lib/transport/SubscriberConnection.cpp

const Guid& signalID = row->ValueAsGuid(signalIDColumn).GetValueOrDefault();

ValueAsGuid returns a temporary Nullable<Guid> and GetValueOrDefault returns a reference to its member, so signalID dangled once the statement ended. It was then passed to SignalIndexCache::AddMeasurementKey. This is publisher side: it determines the signal IDs placed in a subscriber's signal index cache. signalID is now held by value.

The existing tests pass in Release with or without this change; it was only caught by AddressSanitizer.

Testing

Check	Linux (g++ 10.5, Boost 1.92, Release)	Windows (VS 2026 v145, Release x64)
Library and all samples build	OK	OK, 0 warnings
ParseGuid(…, true) before	Fails at -O2 (garbage / all-zero Guids), passes at -O0	Passes
ParseGuid(…, true) after	Passes	Passes
FilterExpressionTests, PublisherCacheIndexTest, ConfigurationFramesTest, SubscriberStartupTest	Pass	Pass
SimpleSubscribe against a local openHistorian	Subscribed with 14 signals	Not run

AddressSanitizer (-fsanitize=address -fsanitize-address-use-after-scope, Linux):

• Original ParseGuid: stack-use-after-scope at Convert.cpp:604; clean after the fix.
• PublisherCacheIndexTest: aborted with stack-use-after-scope under SubscriberConnection.cpp:1410 before the fix; clean after.
• The other samples listed above report nothing.

Not included

• No regression test is added for ParseGuid(…, true); it was checked with a throwaway program linked against the built library.
• No version bump.
• Debug and Win32 configurations were not built.
• The vendored antlr4 runtime and pugixml were not reviewed for the same pattern.

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