v3rpc: return Unavailable instead of Unknown for ErrNotPrimary

[blackwell-systems]

When LeaseRenew returns lease.ErrNotPrimary (e.g. after a leader switch), the error was not mapped in toGRPCErrorMap, causing togRPCError to fall through to status.Error(codes.Unknown, err.Error()). Clients seeing Unknown (code 2) do not know to retry.

This adds ErrGRPCLeaseNotPrimary with codes.Unavailable (14) and maps lease.ErrNotPrimary to it, so clients receive a retryable status code. This is consistent with how ErrLeaderChanged and ErrNoLeader are already mapped to codes.Unavailable.

Changes:

• api/v3rpc/rpctypes/error.go: add ErrGRPCLeaseNotPrimary, ErrLeaseNotPrimary, and the errStringToError mapping
• server/etcdserver/api/v3rpc/util.go: add lease.ErrNotPrimary to toGRPCErrorMap
• server/etcdserver/api/v3rpc/util_test.go: add test case

Tests pass:

ok  go.etcd.io/etcd/server/v3/etcdserver/api/v3rpc (TestGRPCError)
ok  go.etcd.io/etcd/api/v3/v3rpc/rpctypes (TestConvert)

Fixes #21671

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @blackwell-systems. Thanks for your PR.

I'm waiting for a etcd-io member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

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[serathius]

/ok-to-test

[serathius]

Please provide a test

[blackwell-systems]

Added TestLeaseNotPrimaryReturnsUnavailable in 53cf384. It explicitly asserts the gRPC status code is codes.Unavailable, verifying that clients can distinguish this transient leadership error from permanent codes.Unknown failures and retry accordingly.

The existing TestGRPCError table also has a row for the mapping (lease.ErrNotPrimary → rpctypes.ErrGRPCLeaseNotPrimary).

[blackwell-systems]

/retest

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.24%. Comparing base (31ba53a) to head (79f4b60).

Additional details and impacted files

Files with missing lines	Coverage Δ
api/v3rpc/rpctypes/error.go	90.47% <ø> (ø)
server/etcdserver/api/v3rpc/util.go	67.74% <ø> (ø)

... and 29 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #21684      +/-   ##
==========================================
+ Coverage   69.09%   69.24%   +0.14%     
==========================================
  Files         432      432              
  Lines       35544    35544              
==========================================
+ Hits        24560    24613      +53     
+ Misses       9595     9544      -51     
+ Partials     1389     1387       -2     

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