add dependency policy events

[Kexin2000]

What type of PR is this?

/kind feature
/kind cleanup

What this PR does / why we need it:
This PR introduces two key improvements to the dependency distribution mechanism in Karmada:

1. Enhanced Observability: Adds new event reasons to improve visibility into dependency policy conflicts and aggregation.
2. Behavioral Fix: Prevents the dependency controller from overwriting ConflictResolution and PreserveResourcesOnDeletion fields on ResourceBindings (RBs) that are explicitly governed by PropagationPolicy or ClusterPropagationPolicy.

These changes address issues where multi-path distribution could cause field flapping and unpredictable behavior, ensuring more stable and predictable resource management.

Which issue(s) this PR fixes:
Fixes #6000

Special notes for your reviewer:

• Adds the following event reasons in pkg/events/events.go:
  • DependencyPolicyConflict: Indicates multiple parents have divergent dependency policies.
  • DependencyPolicyAggregated: Indicates aggregated dependency policies have been applied.
  • DependencyOverriddenByExplicitPolicy: Indicates dependency path is overridden by explicit policy.
• Updates createOrUpdateAttachedBinding in pkg/dependenciesdistributor/dependencies_distributor.go to:
  • Only set ConflictResolution and PreserveResourcesOnDeletion when the existing RB is dependency-generated (Spec.Placement == nil).
  • Emit a warning event when dependency path settings are ignored due to explicit policy ownership.

Does this PR introduce a user-facing change?:

- Added new event reasons for dependency policy conflicts and aggregation.  
- Dependency controller no longer overwrites [ConflictResolution](http://_vscodecontentref_/0) and [PreserveResourcesOnDeletion](http://_vscodecontentref_/1) fields on explicitly governed ResourceBindings.  

[karmada-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[karmada-bot]

Welcome @Kexin2000! It looks like this is your first PR to karmada-io/karmada 🎉

[gemini-code-assist]

Summary of Changes

Hello @Kexin2000, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly improves the stability and predictability of resource management in Karmada by addressing issues related to multi-path distribution. It enhances the system's ability to communicate dependency policy states through new event reasons and rectifies a behavioral flaw where dependency mechanisms could inadvertently override explicitly defined resource binding configurations. These changes collectively aim to prevent field flapping and ensure that explicit policies are respected, leading to more robust and understandable resource propagation.

Highlights

• Enhanced Observability: Introduced new event reasons (DependencyPolicyConflict, DependencyPolicyAggregated, DependencyOverriddenByExplicitPolicy) to provide better visibility into dependency policy conflicts and aggregation within Karmada's dependency distribution mechanism.
• Behavioral Fix for ResourceBindings: Prevented the dependency controller from overwriting ConflictResolution and PreserveResourcesOnDeletion fields on ResourceBindings (RBs) that are explicitly governed by PropagationPolicy or ClusterPropagationPolicy, ensuring explicit policies take precedence.

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[Copilot]

Pull Request Overview

This PR enhances the dependency distribution mechanism in Karmada by adding observability events and preventing field overrides on explicitly governed ResourceBindings. The changes address issues with multi-path distribution causing field flapping and unpredictable behavior.

• Adds three new event reasons for better visibility into dependency policy conflicts and aggregation
• Modifies dependency controller to respect explicit policy ownership of ResourceBindings
• Prevents overwriting of ConflictResolution and PreserveResourcesOnDeletion fields when ResourceBindings are governed by PropagationPolicy or ClusterPropagationPolicy

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
pkg/events/events.go	Adds three new event reason constants for dependency policy handling
pkg/dependenciesdistributor/dependencies_distributor.go	Updates binding update logic to conditionally set fields and emit warning events

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[Copilot]

The error message format uses string formatting with %s placeholders but the message text says "Ignore" which is grammatically awkward. Consider changing to "Ignoring dependency settings for %s/%s because it is governed by explicit policy."

Suggested change

	"Ignore dependency settings for %s/%s because it is governed by explicit policy.", existBinding.Namespace, existBinding.Name)
	"Ignoring dependency settings for %s/%s because it is governed by explicit policy.", existBinding.Namespace, existBinding.Name)

[gemini-code-assist]

Code Review

This pull request introduces new events for dependency policies and prevents the dependency distributor from overwriting fields on ResourceBindings that are managed by an explicit policy. The changes are logical and address the intended issue. However, I've found one issue with the implementation of the new warning event, which could lead to excessive event logging. My review includes a suggestion to refine the condition for firing this event to make it more meaningful and less noisy.

[gemini-code-assist]

The current condition for triggering a warning event, attachedBinding.Spec.ConflictResolution != "", will always be true because ConflictResolution is a required field with a default value of "Abort". This will cause an event to be logged on every reconciliation for every dependency with an explicit policy, leading to excessive and noisy event logs.

A better approach is to check if the values from the dependency path (attachedBinding) actually differ from what's already on the explicit ResourceBinding (existBinding). This ensures that a warning is only emitted when a meaningful configuration difference is being ignored.

Suggested change

	if attachedBinding.Spec.PreserveResourcesOnDeletion != nil || attachedBinding.Spec.ConflictResolution != "" {
	if !equality.Semantic.DeepEqual(attachedBinding.Spec.PreserveResourcesOnDeletion, existBinding.Spec.PreserveResourcesOnDeletion) || attachedBinding.Spec.ConflictResolution != existBinding.Spec.ConflictResolution {

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 22.22222% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.83%. Comparing base (768f929) to head (7ad6c3f).
⚠️ Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
...ependenciesdistributor/dependencies_distributor.go	22.22%	6 Missing and 1 partial ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6795      +/-   ##
==========================================
+ Coverage   45.75%   45.83%   +0.08%     
==========================================
  Files         689      690       +1     
  Lines       57176    57307     +131     
==========================================
+ Hits        26159    26268     +109     
- Misses      29390    29407      +17     
- Partials     1627     1632       +5     

Flag	Coverage Δ
unittests	45.83% <22.22%> (+0.08%)	⬆️

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