[release/10.0] Load handler DLL with load dir on the path

[github-actions]

Backport of #63773 to release/10.0

/cc @adityamandaleeka

Load handler DLL with load dir on the path

Description

This change updates the handler DLL load call from LoadLibrary to LoadLibraryEx with the flags
LOAD_LIBRARY_SEARCH_DEFAULT_DIRS | LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR

The handler DLL exports CreateApplication as a forwarded export to an architecture-specific DLL. The plain LoadLibrary does not search the handler’s directory when resolving that forwarder. As a result, the loader fails to locate the arch-specific DLL and the scenario breaks (the user gets a 500 error).

Fixes #63772

Customer Impact

Apps may fail to start because the arch-specific implementation for the forwarded export isn't found.

Regression?

• Yes
• No

This bug was introduced in .NET 10 Preview 2 as part of #59483

Risk

• High
• Medium
• Low

Localized change to one load site. Only adds the handler's directory to the probing path for that module's dependency resolution and does not enable PATH/CWD, nor change process-wide state.

Verification

• Manual (required)
• Automated

Packaging changes reviewed?

• Yes
• No
• N/A

---

[wtgodbe]

@adityamandaleeka is this for RC2 or RTM?

[danmoseley]

@wtgodbe it is for RC2 if possible (see Jeff's tactics mail about speculative changes).

Given the change is so localized, my inclination would be to get it into RC2 if we're allowed to today, even though vendor validation didn't yet happen.

[danmoseley]

Mechanistically should we kick the bot to make an rc2 port, or do you do that?

[wtgodbe]

/backport to release/10.0-rc2

[github-actions]

Started backporting to release/10.0-rc2: https://github.com/dotnet/aspnetcore/actions/runs/17981742507

[wtgodbe]

Given the change is so localized, my inclination would be to get it into RC2 if we're allowed to today, even though vendor validation didn't yet happen.

Sounds good, I just kicked the bot. Since this is already green we might as well merge it too

[dotnet-policy-service]

Hi @@github-actions[bot]. This PR was just approved to be included in the upcoming servicing release. Somebody from the @dotnet/aspnet-build team will get it merged when the branches are open. Until then, please make sure all the CI checks pass and the PR is reviewed.