Snapshot reference support

[linglingye001]

ref

[Copilot]

Pull request overview

This PR adds "Snapshot Reference" support to the Azure App Configuration Go provider. Snapshot references allow a key-value setting stored in App Configuration to point to a named snapshot — when loaded, the settings from that snapshot are merged into the configuration. The implementation refactors the existing snapshot loading into a shared helper function, adds content-type detection for snapshot references, and emits a tracing tag when they are used.

Changes:

• Extracts snapshot loading into a reusable loadSnapshotSettings function and adds snapshotSettingsLoader function type to support snapshot reference resolution with dependency injection.
• Adds detection of snapshotReferenceContentType in loadKeyValues, collects snapshot references, and resolves them via the new loadSettingsFromSnapshotRefs method.
• Adds UseSnapshotReference tracing option and SnapshotReferenceTag correlation context tag.

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
azureappconfiguration/azureappconfiguration.go	Core implementation: detection of snapshot reference content type, loadSettingsFromSnapshotRefs, and parseSnapshotReference
azureappconfiguration/settings_client.go	Extracts snapshot loading into loadSnapshotSettings helper; adds snapshotSettingsLoader type
azureappconfiguration/internal/tracing/tracing.go	Adds SnapshotReferenceTag and UseSnapshotReference option to correlation context header
azureappconfiguration/constants.go	Adds snapshotReferenceContentType constant
azureappconfiguration/options.go	Minor whitespace fix
azureappconfiguration/snapshot_test.go	Adds unit tests for parseSnapshotReference and loadSettingsFromSnapshotRefs

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[zhiyuanliang-ms]

I just realized that we introduced a breaking change when supporting snapshot reference for .net provider. This applies for all providers since they all use .net provider as blueprint.
In PR, we added a helper method to load configuration settings from snapshot and we will swallow the 404 if snapshot is not found. There are two code paths now: 1. select/load a snapshot (hard-coded in the code) 2. use a snapshot reference
Previously, if user selected a snapshot and that snapshot is not found, we will throw. Now this behavior change.

@jimmyca15 @avanigupta Is this behavior change intended?

[mrm9084]

@zhiyuanliang-ms I believe this was intentional. We discussed this in my python PR as originally, I didn't catch the error: Azure/azure-sdk-for-python#44116 (comment)

[jimmyca15]

Is this behavior change intended?

Yes.

I just realized that we introduced a breaking change

While I agree there was a change, I'm not sure I would qualify it as breaking. A consumer would have had to depend on exceptions for missing snapshots.