Org upkeep (.github#1): lint baseline, Go 1.27.1, tool pins, core v0.1.5, JSON logs off a terminal

[CMGS]

Implements the per-repo part of cocoonstack/.github#1: revive default rules, nolintlint, Go 1.27.1, the pinned tool versions, projecteru2/core v0.1.5 and JSON log records when stderr is not a terminal (only the sections that apply here).

Commits

• 735921e lint: enable revive default rules
• 96eb380 lint: enable nolintlint, drop unused directives
• b24b174 build: go 1.27.1
• 93de917 build: goreleaser v2.18.2
• 1091179 log: JSON records when stderr is not a terminal
• 291a3a1 deps: projecteru2/core v0.1.5

Notes

• The empty-block drain loop in agent/agent_test.go is now an explicit loop that returns on the first encode error.
• core v0.1.5 moves only indirect lines (sentry-go, genproto/rpc).

JSON logs off a terminal

cocoon-agent bogus: stderr to a file gives {"level":"error","func":"cmd.run",...}; under script -q the console line has ANSI colour codes.

Gates

Run with GOWORK=off against the pinned golangci-lint v2.13.2 (built with go1.27.1):

fmt-check PASS
lint PASS
asl-linux PASS
asl-darwin PASS
asl-windows PASS
test PASS
build PASS

gofumpt v0.12.0 / goimports v0.50.0 are held until the next golangci-lint release vendors them (see the issue).