Add pkg/shardlookup

[ntnn]

Summary

Refactors the cache implemented for cross-shard SA lookup into pkg/shardlookup to be reused.

Related: #4061

What Type of PR Is This?

/kind cleanup

Related Issue(s)

Fixes #

Release Notes

NONE

[Copilot]

Pull request overview

This PR extracts the shard-local vs remote-shard lookup and request coalescing logic (previously embedded in the serviceaccount token getter cache) into a new reusable pkg/shardlookup package, and updates the serviceaccount cache to use the new primitives.

Changes:

• Added pkg/shardlookup.TTLCache (TTL + singleflight request coalescing) and pkg/shardlookup.Lookup (local-or-fetch wrapper).
• Migrated pkg/server/serviceaccount/cache.go to use the new shardlookup abstractions.
• Removed the serviceaccount-specific coalescing_cache.go implementation.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pkg/shardlookup/ttl_cache.go	Introduces a generic TTL + singleflight cache used for cross-shard lookups.
pkg/shardlookup/lookup.go	Adds a reusable “local lister vs remote fetch” lookup wrapper keyed by cluster-aware keys.
pkg/shardlookup/doc.go	Provides package-level guidance on when to use shardlookup vs the cache server.
pkg/server/serviceaccount/cache.go	Switches SA/secret lookup to the new shardlookup cache + lookup wrappers.
pkg/server/serviceaccount/coalescing_cache.go	Deletes the previous serviceaccount-specific coalescing cache implementation.

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[mjudeikis]

/lgtm
/approve

Im not sure about naming of the packages but we can change this later. Or never :D

[kcp-ci-bot]

LGTM label has been added.

Details

Git tree hash: bfd0cd9aa6895135c412ce254f7c5b58d21587bc

[kcp-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mjudeikis

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• OWNERS [mjudeikis]

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[ntnn]

Im not sure about naming of the packages

You and me both :D

[ntnn]

/cherry-pick 0.31

[kcp-ci-bot]

@ntnn: once the present PR merges, I will cherry-pick it on top of 0.31 in a new PR and assign it to you.

Details

In response to this:

/cherry-pick 0.31

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[kcp-ci-bot]

@ntnn: cannot checkout 0.31: error checking out "0.31": exit status 1 error: pathspec '0.31' did not match any file(s) known to git

Details

In response to this:

/cherry-pick 0.31

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[ntnn]

/cherry-pick release-0.31

[kcp-ci-bot]

@ntnn: new pull request created: #4065

Details

In response to this:

/cherry-pick release-0.31

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