Integration branch for PR #5710: Expand OTel fallback exception handling

[Copilot]

Changes proposed in this request

Integration branch for external PR #5710 to enable CI testing. Expands exception handling when OpenTelemetry instrumentation fails to load.

Code changes:

• AbstractPlatformProxy.cs: Catch TypeLoadException and TypeInitializationException in addition to FileNotFoundException when instantiating OTel instrumentation
• Uses pattern matching with when clause for cleaner exception filtering

Context:
Observed in Azure Functions environments with older System.Diagnostics.DiagnosticSource versions. Original issue (#4456) identified FileNotFoundException, but contributor @fowl2 encountered TypeLoadException in production.

Testing

No new tests added. Change expands existing fallback behavior to handle additional exception types in the same code path.

Performance impact

None. Exception handling only triggered when OTel dependencies unavailable (existing failure path).

Documentation

• All relevant documentation is updated.

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Reference: #5710
Credit: Original contribution by @fowl2

Original prompt

Create an integration branch off main to allow CI tests to run for PR #5710 (external fork), and adjust the workflow so the changes can be merged safely.

Context:

• Repo: AzureAD/microsoft-authentication-library-for-dotnet
• Existing PR: Fix fallback where OpenTelemetry instrumentation is not available #5710 ("Fix fallback where OpenTelemetry instrumentation is not available")
• Rationale: tests do not run on forks from external contributors; we want an internal branch/PR path so CI runs.

Tasks:

1. Create a new branch from main named something like integrate/pr-5710-otel-fallback.
2. Bring the commits/changes from PR Fix fallback where OpenTelemetry instrumentation is not available #5710 onto this new branch (prefer merge PR into integration branch, or cherry-pick commits if required).
3. Open a new PR (or retarget existing PR if appropriate) such that the PR head is the integration branch in the main repo and base is main, ensuring CI runs.
4. Ensure the PR description references the original PR Fix fallback where OpenTelemetry instrumentation is not available #5710 and explains why the integration branch exists.
5. Confirm the new PR triggers the expected CI checks and that it is merge-ready.

Acceptance criteria:

• There is a branch in the upstream repo containing PR Fix fallback where OpenTelemetry instrumentation is not available #5710’s changes atop latest main.
• There is an upstream PR that runs CI and can be merged into main.
• Traceability back to Fix fallback where OpenTelemetry instrumentation is not available #5710 is clear.

This pull request was created from Copilot chat.

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