build: upgrade golangci-lint to v2.13.1 and fix resulting lint issues

[bhatnitish]

Why

make lint does not currently work in this repo. It fails before reporting anything:

Error: can't load config: the Go language version (go1.23) used to build
golangci-lint is lower than the targeted Go version (1.25.8)

[email protected] has a toolchain directive forcing it to build with go1.23.6, while go.mod targets Go 1.25.8 — golangci-lint refuses that combination outright, so lint has effectively been unenforced.

Staying on v1 isn't an option: every v1 release, up to and including the final v1.64.8, is built with Go ≤ 1.24 and rejects this module.

This is a prerequisite for adding a Lint job to CI (follow-up PR).

What

Toolchain bump. v1.63.4 → v2.13.1 (built with go1.26.7); module path gains a /v2 suffix. There is no .golangci.yml here, so there's no config to migrate — the only behavioural change is that the default linter set folds gosimple into staticcheck.

34 issues fixed. Worth flagging: golangci-lint caps duplicate messages at 3 by default, which reports only 21. The true count came from --max-same-issues=0 — fixing just the visible 21 would have made the remaining 13 surface immediately.

Linter	n	Fix
errcheck	7	unchecked Close() / os.Setenv / os.Unsetenv returns
staticcheck ST1005	13	capitalized error strings → lowercase
staticcheck QF1004	5	strings.Replace(…, -1) → strings.ReplaceAll
staticcheck QF1008	4	redundant embedded-field selectors
staticcheck QF1003	2	if/else if chain → tagged switch
staticcheck SA1019	2	deprecated NodeSystemInfo.KubeProxyVersion
staticcheck ST1001	1	dot import

Two judgement calls

SA1019 — KubeProxyVersion. I checked whether any non-test code reads it: nothing does, it's purely test fixture data. So the field is dropped rather than suppressed.

ST1001 — dot import in tests/e2e/suite.go. . "gopkg.in/check.v1" is gocheck's documented idiom, and there are 66 *C call sites across 5 files that would need qualifying. Churning the whole e2e suite for a style rule isn't a good trade, so this one is suppressed with a //nolint carrying that rationale.

The QF1008 fixes rely on field promotion, so I checked for shadowing: ctrl.Request embeds types.NamespacedName and defines no String() of its own, and rest.Config embeds ContentConfig. Neither promotion recurses.

Verification

Command	Result
make manager	pass
make vet	pass
make unit-test	pass
make lint	pass — 0 issues uncapped (--max-same-issues=0 --max-issues-per-linter=0)

All changes are behaviour-preserving.

Note

Installing golangci-lint v2.13.1 requires Go ≥ 1.26, so the go command switches toolchains automatically. That will fail anywhere GOTOOLCHAIN=local is pinned.