fix: CNS should not mark itself as ready if it can't write out a conflist.

[paulgmiller]

Reason for Change:
CNS should not signal its healthz till it can write out a conflist. Going ready

1. makes it it harder for both engineers and systems to know CNS isn't getting to a good state.
2. makes it easier for a bad rollout to takea bug to all nodes.

Refactors

1. This moves alot of ncsync logic out of internalapi.go to synchostnc.go
2. It adds a new wait group like object (networkContainerSyncState) to httprestservice
3. Changes direct calls/loops in main to SyncHostNCVersion to use StartSyncHostNCVersionLoop for consistencey and better mangemetn of starting wait
4. has nodesubent also startwat/signal readiness and not write the conflist direcl
5. moves conf list writing to a wait function that also makes sure waits on nc (nodesubbnet and syncHostNCVersion) have signaled.

Tries to hide as much as possible to make movign to subpackage easier in future but pretty tangled with HttpRestServer still.

• uses conventional commit messages
• includes documentation
• adds unit tests
• relevant PR labels added

Notes:

[Copilot]

Pull request overview

This PR introduces a synchronization mechanism to prevent CNS from marking itself as ready before the CNI conflist has been successfully generated. It refactors the SyncHostNCVersion loop code by extracting it into a new file and adds a WaitForNCSynced function that blocks until the conflist is written out.

Key changes:

• Added WaitForNCSynced call in main.go before marking the service as ready
• Refactored duplicate SyncHostNCVersion loop code into a new StartSyncHostNCVersionLoop function
• Moved sync-related functions to a new file synchostnc.go for better code organization

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
cns/service/main.go	Adds WaitForNCSynced call before marking service ready; refactors duplicate SyncHostNCVersion loop initialization to use StartSyncHostNCVersionLoop
cns/restserver/synchostnc.go	New file containing refactored sync functionality including StartSyncHostNCVersionLoop, SyncHostNCVersion, syncHostNCVersion, MustGenerateCNIConflistOnce, and WaitForNCSynced
cns/restserver/restserver.go	Adds ncSynced channel field; removes MustGenerateCNIConflistOnce (moved to synchostnc.go)
cns/restserver/internalapi.go	Removes SyncHostNCVersion and syncHostNCVersion functions (moved to synchostnc.go); removes unused imports
cns/healthserver/healthz.go	Minor formatting improvement (adds blank line)

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[Copilot]

The ncSynced channel is closed before the conflist generation completes. If Generate() or Close() fail and panic, the channel will already be closed, potentially allowing WaitForNCSynced to return success even though the conflist generation failed. Consider moving close(service.ncSynced) to after both Generate() and Close() succeed, or handle it in a defer that checks if the operations succeeded.

[Copilot]

The ncSynced channel is unconditionally recreated without protection. If StartSyncHostNCVersionLoop is called multiple times (which could happen in error scenarios or test code), it will create a new channel and orphan any goroutines waiting on the previous channel. Consider using sync.Once to ensure the channel is only initialized once, or return an error if it's already initialized, as suggested by the comment on line 21.

[paulgmiller]

bad comment.

[paulgmiller]

Also can revert though maybe a commetn here is good.

[paulgmiller]

revert or push ready channel into here.