feat: retarget Go standards baseline to Go 1.26 (1.25-compatible)

[sebastian-iancu]

Summary

Moves the plugin's Go standards baseline from Go 1.25 to Go 1.26 (minimum 1.26.4), while keeping the guidance effective for 1.25 modules through the existing Since/go.mod version-gating in go-idioms. This satisfies "act effective for modern code (1.26+) while still supporting 1.25."

Grounded in the Go 1.26 release notes and the go fix blog post.

New Go 1.26 material added to the skills:

• go-idioms — new(expr) idiom (allocate + initialize a pointer in one step, ideal for optional/JSON pointer fields) as a Since 1.26 row; a note on self-referencing generic type parameters (type Adder[A Adder[A]] interface{ Add(A) A }); and go fix ./... reframed as the canonical, toolchain-native modernizer runner on 1.26.
• go-testing — testing/cryptotest.SetGlobalRandom for deterministic crypto tests; note that the pre-1.25 GOEXPERIMENT=synctest (synctest.Run) API was removed in Go 1.26.
• go-concurrency — experimental goroutineleak profile in runtime/pprof as a toolchain-native complement to goleak.

Baseline / tooling updates:

• Standards baseline moved to Go 1.26 across go-coding, go-linting, go-explain, the go-reviewer agent, and rules/go-context.mdc; go fix ./... framed as the native modernizer runner with golangci-lint --enable-only=modernize retained for CI reproducibility and older toolchains.
• docs/install.md + README.md — minimum host toolchain raised to Go 1.26.x (1.26.4+); tarball example → go1.26.4; gopls pin → v0.22.x (the gopls line adding Go 1.26 support).
• Version bumped to 0.3.0 in both manifests; CHANGELOG 0.3.0 section added; AGENTS.md status line updated.

Checklist

• ./scripts/validate.sh passes (or claude plugin validate . if Python is unavailable)
• claude plugin validate . passes
• Skill / command / agent triggering tested locally (see docs/testing.md) — content-only change; not exercised in this environment
• Cursor install tested locally when manifest, rule, or hook content changed (see docs/install.md) — not exercised in this environment
• Both manifests kept in sync when metadata changed: .claude-plugin/plugin.json and .cursor-plugin/plugin.json
• Cursor rule files and the .cursor-plugin/plugin.json path map kept in step with the components that exist
• Version bumped and CHANGELOG.md updated (if component content changed) — see docs/versioning.md
• Docs synced (AGENTS.md, README.md, hooks/session-start.sh) when components were added or renamed

🤖 Generated with Claude Code

https://claude.ai/code/session_016DwDkMcyVnq9RqzJK7CHKu

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Generated by Claude Code

[sebastian-iancu]

Review — LGTM ✅ (merge-ready)

Reviewed with /review + plugin-dev:skill-development + plugin-dev:agent-development. Because this plugin's value is factual grounding in authoritative Go sources, I verified every net-new Go 1.26 claim against the release notes and pkg.go.dev (Go 1.26 shipped Feb 2026, after my training cutoff) rather than trusting memory.

Factual accuracy — all verified

Claim	Verification	Status
new(expr) allocate+init a pointer	Release notes: "the built-in new… now allows its operand to be an expression"; example Age: new(yearsSince(born))	✅
new(expr) auto-fixed by modernize/go fix	newexpr analyzer exists in x/tools/.../modernize/newexpr.go, runnable via go fix on 1.26	✅
go fix revamped as the modernizer home	Release notes: "now the home of Go's modernizers… builds atop the same analysis framework as go vet"	✅
testing/cryptotest.SetGlobalRandom	pkg.go.dev/testing/cryptotest: SetGlobalRandom(t, seed) deterministic source for crypto/rand	✅
experimental goroutineleak profile	Release notes: profile named goroutineleak, enabled via GOEXPERIMENT=goroutineleakprofile	✅
synctest.Run removed in 1.26	Go 1.25 notes + tracking issue golang/go#74012 "remove Run in Go 1.26"; 1.26.4 shows only Test+Wait	✅
self-referential generic type params	Release notes: exact type Adder[A Adder[A]] example matches	✅
Go 1.26 Feb 2026 / 1.26.4 Jun 2 2026 / gopls v0.22.0 May 15 2026	release timeline consistent	✅

Conventions / parity / hygiene — clean

• Skill descriptions stay third-person with trigger phrases; go-reviewer keeps tools: (not allowed-tools:).
• Both manifests → 0.3.0, valid JSON, Cursor path keys intact.
• SemVer minor bump correct; CHANGELOG follows Keep a Changelog; historical 1.25 entries correctly left untouched.
• Retarget is complete — every residual 1.25 is intentional; session-start.sh has no stale version string.

Optional polish (non-blocking) — being fixed in a follow-up commit

1. goroutineleak needs a build flag — go-concurrency says the runtime "ships" the profile, but it only appears with GOEXPERIMENT=goroutineleakprofile at build time. Noting the flag saves a fruitless hunt.
2. SetGlobalRandom can't run under t.Parallel() — it's process-global and forbidden in parallel tests. go-testing heavily promotes t.Parallel(), so a caveat (and a nod to the seed arg) prevents a footgun.
3. go-idioms "Over" column slightly broad — the newexpr modernizer targets the ptr[T](v) helper form; the inline tmp := v; &tmp pattern is more a review catch than an auto-fix. Minor precision.

[sebastian-iancu]

✅ Resolved in d0a7c22 — all three review nits addressed:

• go-concurrency: goroutineleak profile now notes it needs GOEXPERIMENT=goroutineleakprofile at build time.
• go-testing: SetGlobalRandom(t, seed) now surfaces the seed arg and the process-global caveat (not usable under t.Parallel()).
• go-idioms: "Over" column now distinguishes the newexpr-auto-fixed ptr[T](v) helper from the review-catch tmp := v; &tmp inline form.

Docs-only prose refinements; ./scripts/validate.sh and claude plugin validate . both pass.