AB#3752409: Add platform broker telemetry tests and documentation

[Lalima Sharda (lalimasharda)]

Summary

Correct the platform broker performance documentation to describe the final nested extension-handshake telemetry model and its queryable outcome signals.

Add focused telemetry coverage for an unavailable extension, an extension handshake timeout, and user cancellation returned by the platform broker.

Implements

• AB#3752409 — Platform brokering telemetry improvements
• AB#3752410 — Improve platform brokering observability

How to validate

• Run the focused PlatformAuthExtensionHandler and PlatformAuthInteractionClient tests.
• Verify unavailable and timed-out extension discovery emit their expected root-event context without a standalone handshake event.
• Verify broker user cancellation is recorded as BrowserAuthError/user_cancelled.
• Verify the performance documentation provides query dimensions and a request-level troubleshooting workflow.

Validation

• 94 focused tests passed.
• MSAL Common and MSAL Browser builds passed.
• Browser formatting, API Extractor, and Beachball checks passed.
• Repository-wide browser source lint reports pre-existing errors in untouched files.

assistance: agentic-cli
type: telemetry
agent-tool: copilot-cli
agent-model: gpt-5.6-sol
work-item: AB#3752409

[Copilot]

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Copilot review overview

Review effort: Lite
Findings: 3 · 1

Open (4)

• The table rows are prefixed with ||, which renders as an extra empty column in many Markdown… · New
• This callback registration is not removed, which can leak into later tests and make events… · New
• toHaveBeenCalledWith requires the first argument object to match exactly. If the implementation… · New
• If createProviderEvent is undefined, toMatchObject will fail but Jest will continue executing… · New

What changed in this PR

Updates platform broker performance documentation and adds focused test coverage to ensure telemetry correctly records extension discovery outcomes (unavailable/timeout) and broker user-cancellation.

Changes:

• Add a test asserting broker user cancellation maps to BrowserAuthError/user_cancelled telemetry.
• Expand extension handler tests to validate timeout behavior emits only the root createProvider event context (and no standalone handshake event).
• Update performance documentation to describe nested extension-handshake telemetry fields and queryable outcome signals.

File	Description
lib/​msal-browser/​test/​interaction_client/​PlatformAuthInteractionClient.spec.ts	Adds test coverage for broker user-cancellation telemetry mapping.
lib/​msal-browser/​test/​broker/​PlatformAuthExtensionHandler.spec.ts	Strengthens timeout test and asserts root-event context + no handshake event emission.
lib/​msal-browser/​docs/​performance.md	Documents the nested platform broker telemetry model and recommended query dimensions.

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