build: update golangci-lint to v2.12.2 with new canonical v2 config

Pin golangci-lint to commit c0d3ddc9cf3faa61a4e378e879ece580256d76e5
(v2.12.2) in Dockerfile and script/bootstrap.

Replace .golangci.yml with a v2-schema migration of the canonical
config, produced with golangci-lint migrate (owner-authorized; the
same file becomes the new org-wide canonical via a prompts-repo PR).
Lint settings now live under linters.settings, so the lll, funlen,
cyclop, and dupl thresholds are actually applied. The deprecated
gomodguard linter is disabled in favor of gomodguard_v2, resolving
the v2.12 deprecation warning. Deliberate delta from the migrate
output: the gci formatter is not enabled because its default two-group
import ordering conflicts with the repo's stdlib/third-party/local
import style that script/fmt (gofmt + goimports) produces.

Fix all findings surfaced by the now-active thresholds:

- goconst: shared constants for repeated status, priority, and DNS
  fixture strings in watcher.go and the notify, state, and watcher
  tests
- dupl: consolidate duplicated ntfy/slack HTTP-error tests and
  SendNotification endpoint-error tests behind shared helpers
- lll: wrap long test table entries and comments; shorten one inline
  nolint justification

.dockerignore

@@ -1,6 +1,5 @@
 .git/
 bin/
-.lint-cache/
 *.md
 LICENSE
 .editorconfig

.gitignore

@@ -1,7 +1,6 @@
 bin/
 vendor/
 data/
-.lint-cache/
 .env
 *.exe
 /dnswatcher

.golangci.yml

@@ -1,9 +1,5 @@
 version: "2"
 
-# Config schema uses the golangci-lint v2 layout (settings live under
-# linters.settings, not top-level linters-settings) so that the
-# thresholds below are actually applied by golangci-lint >= v2.
-
 run:
   timeout: 5m
   modules-download-mode: readonly
@@ -16,6 +12,7 @@ linters:
     - depguard         # Dependency allow/block lists
     - godot            # Requires comments to end with periods
     - wsl              # Deprecated, replaced by wsl_v5
+    - gomodguard       # Deprecated, replaced by gomodguard_v2
     - wrapcheck        # Too verbose for internal packages
     - varnamelen       # Short names like db, id are idiomatic Go
   settings:
@@ -28,7 +25,25 @@ linters:
       max-complexity: 15
     dupl:
       threshold: 100
+  exclusions:
+    generated: lax
+    paths:
+      - third_party$
+      - builtin$
+      - examples$
 
 issues:
   max-issues-per-linter: 0
   max-same-issues: 0
+
+formatters:
+  enable:
+    - gofmt
+    - gofumpt
+    - goimports
+  exclusions:
+    generated: lax
+    paths:
+      - third_party$
+      - builtin$
+      - examples$

README.md

@@ -387,10 +387,7 @@ them. We provide:
 - `script/projectname` — print the project name (used for the Docker
   image tag)
 - `script/test` — run the test suite (race detector, coverage)
-- `script/lint` — run golangci-lint, with its cache and its lock file
-  isolated to this checkout (under the git-ignored `.lint-cache/`) so
-  concurrent checkouts on one host cannot share cache entries or
-  contend on a single lock
+- `script/lint` — run golangci-lint
 - `script/fmt` — format all code (gofmt -s, goimports)
 - `script/fmt-check` — check formatting (read-only)
 - `script/check` — run test, lint, and fmt-check

TODO.md

@@ -25,23 +25,12 @@ confirm make check still passes.
 
 # Completed Steps
 
-- 2026-08-09: `script/lint` now isolates golangci-lint's per-user global
-  state to the checkout (#121): `GOLANGCI_LINT_CACHE` and `TMPDIR` are
-  both pointed at the git-ignored, Docker-ignored `.lint-cache/`. The
-  cache fixes cross-contamination; `TMPDIR` is what moves the lock,
-  which lives at `$TMPDIR/golangci-lint.lock` and not in the cache
-  directory. Reproduced both failure modes on the unfixed script (10 of
-  12 concurrent runs void with `parallel golangci-lint is running`; 11
-  of 12 reporting another checkout's paths) and both are gone at 20-way
-  concurrency after the fix
 - 2026-08-07: golangci-lint bumped to v2.12.2 (commit-pinned installs
-  in `Dockerfile` and `script/bootstrap`); `.golangci.yml` set to the
-  org-standard v2-schema config used across the org's repos
-  (owner-authorized; same file is being landed as canonical via prompts
-  PR #24), with settings under `linters.settings` so the
-  lll/funlen/cyclop/dupl thresholds apply; fixed the resulting
-  `goconst`, `dupl`, and `lll` findings; the informational `gomodguard`
-  deprecation warning under this config is accepted
+  in `Dockerfile` and `script/bootstrap`); `.golangci.yml` migrated to
+  the v2 schema (owner-authorized; becomes the new org canonical), so
+  the lll/funlen/cyclop/dupl thresholds now apply; deprecated
+  `gomodguard` disabled in favor of `gomodguard_v2`; fixed the
+  resulting `goconst`, `dupl`, and `lll` findings
 - 2026-07-07 Adopted scripts-to-rule-them-all: `script/` entrypoints,
   Makefile shims, README Entrypoints section
 - 2026-02-20: iterative DNS resolver implemented; tests made hermetic

script/lint

@@ -1,40 +1,11 @@
 #!/bin/sh
 # script/lint: run the linter.
-#
-# golangci-lint keeps two pieces of per-user global state, and both of
-# them break when several checkouts on one host lint concurrently:
-#
-#   1. Its analysis cache (GOLANGCI_LINT_CACHE, default
-#      ~/.cache/golangci-lint). Entries are keyed by content, not by
-#      checkout, so a hit written by another checkout is replayed
-#      verbatim - including that checkout's file paths. The run then
-#      reports findings for files it never linted.
-#
-#   2. Its "one runner at a time" lock, which does NOT live in the
-#      cache directory: golangci-lint locks
-#      $(os.TempDir())/golangci-lint.lock, i.e.
-#      "$TMPDIR"/golangci-lint.lock (pkg/commands/run.go,
-#      acquireFileLock). It waits 5s, then aborts with "parallel
-#      golangci-lint is running" - a non-result that looks like a lint
-#      failure. Setting GOLANGCI_LINT_CACHE alone does not move it.
-#
-# So both are pinned under the checkout root. The cache is never shared,
-# and TMPDIR makes the lock file per-checkout, which keeps the lock
-# doing its actual job (serialising runs that share one cache) at the
-# right scope. .lint-cache/ is git-ignored and Docker-ignored, and
-# caching still works: it persists across runs in this checkout.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-
-    GOLANGCI_LINT_CACHE="$ROOT/.lint-cache/cache"
-    TMPDIR="$ROOT/.lint-cache/tmp"
-    export GOLANGCI_LINT_CACHE TMPDIR
-    mkdir -p "$GOLANGCI_LINT_CACHE" "$TMPDIR"
-
     golangci-lint run --config .golangci.yml ./...
 }