feat: decouple informer cache population and event handling

[weng271190436]

Description of your changes

decouple informer cache population and event handling

This is a pre-requisite for #366 to make validating webhook on follower hub agents work.

If I want to run a leader hub agent and multiple followers, the followers need to run webhook validation, which requires informer cache. However, the informer cache is populated by change detector, which only runs on leader replica.

Previously, change detector calls AddDynamicResources to add informer and attach event handler

Now, I am changing it so that a new controller informer populator starts the informer caches while change detector attaches event handler to the informer caches.

I have:

• Run make reviewable to ensure this PR is ready for review.

How has this code been tested

Special notes for your reviewer

[Copilot]

Pull request overview

This PR decouples informer cache population from event handling to enable webhook validation on follower hub agents. Previously, the ChangeDetector created informers and added event handlers in one step, which only ran on the leader. Now, a new InformerPopulator controller creates informers on all pods (leader and followers) while the ChangeDetector (leader-only) adds event handlers to those informers.

Key changes:

• Introduced InformerPopulator that runs on all pods to populate informer caches
• Refactored ChangeDetector to only add event handlers to existing informers
• Extracted shared resource discovery logic into reusable helper functions

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
pkg/resourcewatcher/informer_populator.go	New controller that discovers resources and creates informers without handlers on all pods
pkg/resourcewatcher/informer_populator_test.go	Comprehensive test coverage for the new InformerPopulator
pkg/resourcewatcher/change_dector.go	Refactored to use shared discovery logic and only add event handlers
pkg/resourcewatcher/change_detector_test.go	Tests for the refactored ChangeDetector behavior
pkg/resourcewatcher/resource_collector.go	Extracted shared helper functions for resource discovery and filtering
pkg/resourcewatcher/resource_collector_test.go	Tests for the shared resource discovery helpers
pkg/utils/informer/informermanager.go	Added new interface methods: CreateInformerForResource and AddEventHandlerToInformer
pkg/utils/informer/informermanager_test.go	Tests for the new informer manager methods
pkg/utils/informer/readiness/readiness.go	Updated comment to reference InformerPopulator instead of ChangeDetector
cmd/hubagent/workload/setup.go	Wired up InformerPopulator and ChangeDetector in the hub agent
test/utils/handler/handler.go	New test utility for testing event handlers
test/utils/informer/manager.go	Added stub implementations for new interface methods

[codecov]

Codecov Report

❌ Patch coverage is 83.58209% with 11 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/resourcewatcher/resource_collector.go	54.54%	3 Missing and 2 partials ⚠️
pkg/resourcewatcher/change_dector.go	50.00%	1 Missing and 1 partial ⚠️
pkg/resourcewatcher/informer_populator.go	88.88%	1 Missing and 1 partial ⚠️
pkg/utils/informer/informermanager.go	90.47%	1 Missing and 1 partial ⚠️

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