When an assembly fails to load, the FileLoadException/FileNotFoundException
now includes the name of the requesting (parent) assembly in the FusionLog
property. This helps diagnose dependency chain issues by showing which
assembly triggered the failed load.

The information flows from the native AssemblySpec::GetParentAssembly()
through EEFileLoadException::CreateThrowable() to the managed exception's
FusionLog property, which is displayed in ToString() output.

Fixes #9185

Co-authored-by: elinor-fung <[email protected]>

Walk the inner exception chain to build the full dependency path.
When A→B→C→D and D fails, D's FusionLog now shows:

  Requesting assembly: 'C'
  Requesting assembly: 'B'
  Requesting assembly: 'A'

At each Throw(AssemblySpec*) level, the current parent assembly name
is appended to every inner EEFileLoadException's chain. The managed
FormatRequestingAssemblyChain helper formats each newline-separated
name with the "Requesting assembly:" resource string.

Co-authored-by: elinor-fung <[email protected]>

…dd tests

The requesting assembly chain is now appended to the exception's Message
property instead of FusionLog. This means users see the chain directly
in the exception message when it is thrown, without needing to inspect
FusionLog separately.

Added tests for all three exception types (FileLoadException,
FileNotFoundException, BadImageFormatException) that verify:
- Single requesting assembly appears in Message
- Multiple requesting assemblies (chain) appear in Message
- FusionLog remains null

Co-authored-by: elinor-fung <[email protected]>

…missing transitive dependency

Remove the 6 reflection-based tests that invoked private constructors via
reflection from BadImageFormatExceptionTests, FileLoadExceptionTests, and
FileNotFoundExceptionTests.

Add an integration test in System.Runtime.Loader.Tests that creates a real
dependency chain (Root -> Mid -> Leaf) where the transitive dependency
(Leaf) is missing at runtime. The test verifies that a FileNotFoundException
is thrown with the correct missing assembly name when the chain is exercised.

Three helper assembly projects are added:
- MissingDependency.Leaf (not deployed via PrivateAssets=all)
- MissingDependency.Mid (depends on Leaf)
- MissingDependency.Root (depends on Mid)

Co-authored-by: elinor-fung <[email protected]>

The test now asserts that the FileNotFoundException message contains
"MissingDependency.Mid" (the requesting assembly), verifying that the
entire dependency chain is reported in the exception message, not just
the missing assembly file name.

Co-authored-by: elinor-fung <[email protected]>

The test now asserts that both MissingDependency.Mid and
MissingDependency.Root appear in the exception message, verifying
the entire dependency chain (Root → Mid → Leaf) is reported.

Co-authored-by: elinor-fung <[email protected]>

…nsitive root

The runtime correctly includes the immediate requesting assembly (Mid)
in the FileNotFoundException message, but does not include the full
transitive chain (Root). The chain-building code in clrex.cpp only
propagates when there are nested EEFileLoadException inner exceptions,
which doesn't apply in this single-level missing dependency scenario.

Co-authored-by: elinor-fung <[email protected]>
Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/aefe2c66-6ab2-450f-a995-01336b6c0328

…ore Root assertion

Co-authored-by: elinor-fung <[email protected]>
Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/2526f574-f7a8-4834-991a-6d60b25ed913

…::Throw

The dependency chain comes from the binding cache walk, not from inner
exceptions. An exception is only thrown for the missing dependency itself,
so walking inner exceptions to propagate requesting assembly chains is
unnecessary.

Co-authored-by: elinor-fung <[email protected]>
Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/c54f4451-c7fd-4071-a6fc-57dbfb164795

…g assembly only

Co-authored-by: elinor-fung <[email protected]>
Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/19532b90-dceb-4aa5-bb93-6744037be55c