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

.golangci.yml

@@ -12,21 +12,38 @@ 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
-
-linters-settings:
-  lll:
-    line-length: 88
-  funlen:
-    lines: 80
-    statements: 50
-  cyclop:
-    max-complexity: 15
-  dupl:
-    threshold: 100
+  settings:
+    lll:
+      line-length: 88
+    funlen:
+      lines: 80
+      statements: 50
+    cyclop:
+      max-complexity: 15
+    dupl:
+      threshold: 100
+  exclusions:
+    generated: lax
+    paths:
+      - third_party$
+      - builtin$
+      - examples$
 
 issues:
-  exclude-use-default: false
   max-issues-per-linter: 0
   max-same-issues: 0
+
+formatters:
+  enable:
+    - gofmt
+    - gofumpt
+    - goimports
+  exclusions:
+    generated: lax
+    paths:
+      - third_party$
+      - builtin$
+      - examples$

Dockerfile

@@ -4,8 +4,8 @@ FROM golang@sha256:f6751d823c26342f9506c03797d2527668d095b0a15f1862cddb4d927a7a4
 
 RUN apk add --no-cache git make gcc musl-dev binutils-gold
 
-# golangci-lint v2.10.1
-RUN go install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@5d1e709b7be35cb2025444e19de266b056b7b7ee
+# golangci-lint v2.12.2, 2026-08-07
+RUN go install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@c0d3ddc9cf3faa61a4e378e879ece580256d76e5
 # goimports v0.42.0
 RUN go install golang.org/x/tools/cmd/goimports@009367f5c17a8d4c45a961a3a509277190a9a6f0
 

README.md

@@ -17,6 +17,26 @@ without requiring an external database.
 
 ---
 
+## No DNS mocking. Ever.
+
+**DNS is never mocked in this project — not in tests, not anywhere else.**
+No mock resolvers, no fake DNS servers, no stubbed lookups.
+
+dnswatcher's entire purpose is correct behavior against the real DNS.
+Tests exercise real iterative resolution against live nameservers by
+design; a test suite that passes against a mock proves nothing about the
+one thing this program exists to do.
+
+When live tests are flaky, that is a robustness problem, and it gets
+fixed with robustness: retries with backoff, querying multiple
+independent nameservers, longer timeouts — or explicit opt-in gating
+decided by the project owner. Never with mocks.
+
+Contributions that introduce mocked, faked, or stubbed DNS will be
+rejected.
+
+---
+
 ## Features
 
 ### DNS Domain Monitoring (Apex Domains)

TESTING.md

@@ -2,10 +2,8 @@
 
 ## DNS Resolution Tests
 
-All tests that involve DNS resolution — in every package, including
-consumers of the resolver such as the watcher — **MUST** use live
-queries against real DNS servers. No mocking, faking, or stubbing of
-DNS at any layer is permitted.
+All resolver tests **MUST** use live queries against real DNS servers.
+No mocking of the DNS client layer is permitted.
 
 ### Rationale
 
@@ -14,8 +12,6 @@ the full delegation chain. Mocked responses cannot faithfully represent
 the variety of real-world DNS behavior (truncation, referrals, glue
 records, DNSSEC, varied response times, EDNS, etc.). Testing against
 real servers ensures the resolver works correctly in production.
-Robustness comes from handling real-world DNS behavior with tolerant
-assertions and sensible timeouts, not from mocks.
 
 ### Constraints
 
@@ -28,14 +24,11 @@ assertions and sensible timeouts, not from mocks.
 - Flaky failures from transient network issues are acceptable and
   should be investigated as potential resolver bugs, not papered over
   with mocks or skip flags
-- Watcher change-detection tests seed a synthetic *previous state*
-  and compare it against fresh live lookups; the DNS side is never
-  faked
 
 ### What NOT to do
 
-- **Do not mock `DNSClient`**, the watcher's `DNSResolver` interface,
-  or any other DNS abstraction — in any package, for any reason
+- **Do not mock `DNSClient`** for resolver tests (the mock constructor
+  exists for unit-testing other packages that consume the resolver)
 - **Do not add `-short` flags** to skip slow tests
 - **Do not increase `-timeout`** to hide hanging queries
 - **Do not modify linter configuration** to suppress findings

TODO.md

@@ -14,10 +14,7 @@ pre-1.0. No git tags. Core resolver work in flight on feature/resolver
 (dirty: internal/resolver/resolver_test.go). Local checkout has diverged
 from origin: origin/main is 8 commits ahead (watcher orchestrator,
 unified TARGETS) and origin/feature/resolver already contains the full
-iterative resolver implementation. DNS mocking is banned in this repo
-(see `TESTING.md`): all tests use live DNS only. The hermetic mocked
-tests previously noted on `feature/resolver` are gone from its current
-tip, which carries a live-DNS suite against `*.dns.sneak.cloud`.
+iterative resolver implementation with hermetic mocked tests.
 
 # Next Step
 
@@ -28,15 +25,16 @@ confirm make check still passes.
 
 # Completed Steps
 
-- 2026-08-07: DNS mocking removed from the entire test suite; watcher
-  tests now drive the real iterative resolver against live DNS and
-  `TESTING.md` bans DNS mocks in every package (`remove-dns-mocking`
-  branch)
+- 2026-08-07: golangci-lint bumped to v2.12.2 (commit-pinned installs
+  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
-  with mocked DNS (origin/feature/resolver, unmerged; superseded — DNS
-  mocking is banned, see `TESTING.md`)
+  with mocked DNS (origin/feature/resolver, unmerged)
 - 2026-02-20: CI actions and go install refs pinned to commit SHAs;
   Gitea Actions workflow for make check (origin/ci/make-check, unmerged)
 - 2026-02-20: watcher monitoring orchestrator merged to main (#8)
@@ -63,9 +61,8 @@ Branch reconciliation:
 - Sync local checkout with origin: local main is 8 commits behind
   origin/main; local feature/resolver has diverged from
   origin/feature/resolver, which already implements the resolver
-- Merge in-flight branches to main once green: feature/resolver
-  (confirm its tests remain live-DNS — DNS mocking is banned, see
-  `TESTING.md`), ci/make-check, feature/portcheck-implementation,
+- Merge in-flight branches to main once green: feature/resolver,
+  ci/make-check, feature/portcheck-implementation,
   feature/tlscheck-implementation
 
 Resolver (plan from untracked TODO.md; largely implemented on
@@ -149,7 +146,6 @@ Infrastructure notes (from untracked TODO.md):
 - Module path sneak.berlin/go/dnswatcher differs from the git.eeqj.de
   remote intentionally; do not "fix" it
 - Dependencies: github.com/miekg/dns, golang.org/x/net/publicsuffix
-- Resolver tests originally used live DNS against `*.dns.sneak.cloud`
-  (required records documented in the test file header); `main` now
-  tests against live public DNS. DNS mocking is banned (see
-  `TESTING.md`); never reintroduce hermetic mocked DNS tests
+- Resolver tests originally used live DNS against *.dns.sneak.cloud
+  (required records documented in the test file header); origin now has
+  mocked hermetic tests, keep them hermetic

internal/config/classify_test.go

@@ -17,13 +17,33 @@ func TestClassifyDNSName(t *testing.T) {
 	}{
 		{name: "apex domain simple", input: "example.com", want: config.DNSNameTypeDomain},
 		{name: "hostname simple", input: "www.example.com", want: config.DNSNameTypeHostname},
-		{name: "apex domain multi-part TLD", input: "example.co.uk", want: config.DNSNameTypeDomain},
-		{name: "hostname multi-part TLD", input: "api.example.co.uk", want: config.DNSNameTypeHostname},
+		{
+			name:  "apex domain multi-part TLD",
+			input: "example.co.uk",
+			want:  config.DNSNameTypeDomain,
+		},
+		{
+			name:  "hostname multi-part TLD",
+			input: "api.example.co.uk",
+			want:  config.DNSNameTypeHostname,
+		},
 		{name: "public suffix itself", input: "co.uk", wantErr: true},
 		{name: "empty string", input: "", wantErr: true},
-		{name: "deeply nested hostname", input: "a.b.c.example.com", want: config.DNSNameTypeHostname},
-		{name: "trailing dot stripped", input: "example.com.", want: config.DNSNameTypeDomain},
-		{name: "uppercase normalized", input: "WWW.Example.COM", want: config.DNSNameTypeHostname},
+		{
+			name:  "deeply nested hostname",
+			input: "a.b.c.example.com",
+			want:  config.DNSNameTypeHostname,
+		},
+		{
+			name:  "trailing dot stripped",
+			input: "example.com.",
+			want:  config.DNSNameTypeDomain,
+		},
+		{
+			name:  "uppercase normalized",
+			input: "WWW.Example.COM",
+			want:  config.DNSNameTypeHostname,
+		},
 	}
 
 	for _, tt := range tests {

internal/notify/delivery_test.go

@@ -25,6 +25,20 @@ const (
 	colorDefault = "#6c757d"
 )
 
+// Priority strings used across multiple tests.
+const (
+	prioError   = "error"
+	prioWarning = "warning"
+	prioSuccess = "success"
+	prioInfo    = "info"
+	prioUnknown = "unknown"
+	prioDefault = "default"
+	prioUrgent  = "urgent"
+)
+
+// testHost is the hostname used in request construction tests.
+const testHost = "example.com"
+
 // errSimulated is a static error for transport failures.
 var errSimulated = errors.New("simulated transport failure")
 
@@ -101,13 +115,13 @@ func TestNtfyPriority(t *testing.T) {
 		input string
 		want  string
 	}{
-		{"error", "urgent"},
-		{"warning", "high"},
-		{"success", "default"},
-		{"info", "low"},
-		{"", "default"},
-		{"unknown", "default"},
-		{"critical", "default"},
+		{prioError, prioUrgent},
+		{prioWarning, "high"},
+		{prioSuccess, prioDefault},
+		{prioInfo, "low"},
+		{"", prioDefault},
+		{prioUnknown, prioDefault},
+		{"critical", prioDefault},
 	}
 
 	for _, tc := range cases {
@@ -134,12 +148,12 @@ func TestSlackColor(t *testing.T) {
 		input string
 		want  string
 	}{
-		{"error", colorError},
-		{"warning", colorWarning},
-		{"success", colorSuccess},
-		{"info", colorInfo},
+		{prioError, colorError},
+		{prioWarning, colorWarning},
+		{prioSuccess, colorSuccess},
+		{prioInfo, colorInfo},
 		{"", colorDefault},
-		{"unknown", colorDefault},
+		{prioUnknown, colorDefault},
 		{"critical", colorDefault},
 	}
 
@@ -165,7 +179,7 @@ func TestNewRequest(t *testing.T) {
 
 	target := &url.URL{
 		Scheme: "https",
-		Host:   "example.com",
+		Host:   testHost,
 		Path:   "/webhook",
 	}
 	body := bytes.NewBufferString("hello")
@@ -187,9 +201,9 @@ func TestNewRequest(t *testing.T) {
 		)
 	}
 
-	if req.Host != "example.com" {
+	if req.Host != testHost {
 		t.Errorf(
-			"Host = %q, want %q", req.Host, "example.com",
+			"Host = %q, want %q", req.Host, testHost,
 		)
 	}
 
@@ -217,7 +231,7 @@ func TestNewRequestPreservesContext(t *testing.T) {
 		ctxKey("k"),
 		"v",
 	)
-	target := &url.URL{Scheme: "https", Host: "example.com"}
+	target := &url.URL{Scheme: "https", Host: testHost}
 
 	req := notify.NewRequestForTest(
 		ctx, http.MethodGet, target, http.NoBody,
@@ -289,10 +303,10 @@ func TestSendNtfyHeaders(t *testing.T) {
 		)
 	}
 
-	if captured.priority != "urgent" {
+	if captured.priority != prioUrgent {
 		t.Errorf(
 			"Priority header = %q, want %q",
-			captured.priority, "urgent",
+			captured.priority, prioUrgent,
 		)
 	}
 
@@ -311,10 +325,10 @@ func TestSendNtfyAllPriorities(t *testing.T) {
 		input string
 		want  string
 	}{
-		{"error", "urgent"},
-		{"warning", "high"},
-		{"success", "default"},
-		{"info", "low"},
+		{prioError, prioUrgent},
+		{prioWarning, "high"},
+		{prioSuccess, prioDefault},
+		{prioInfo, "low"},
 	}
 
 	for _, tc := range priorities {
@@ -356,56 +370,69 @@ func TestSendNtfyAllPriorities(t *testing.T) {
 	}
 }
 
-func TestSendNtfyClientError(t *testing.T) {
-	t.Parallel()
+// assertSendStatusError verifies that send returns an error
+// wrapping wantErr when the server responds with status.
+func assertSendStatusError(
+	t *testing.T,
+	status int,
+	wantErr error,
+	send func(*notify.Service, *url.URL) error,
+) {
+	t.Helper()
 
 	srv := httptest.NewServer(
 		http.HandlerFunc(
 			func(w http.ResponseWriter, _ *http.Request) {
-				w.WriteHeader(http.StatusForbidden)
+				w.WriteHeader(status)
 			}),
 	)
 	defer srv.Close()
 
 	svc := notify.NewTestService(srv.Client().Transport)
-	topicURL, _ := url.Parse(srv.URL)
+	target, _ := url.Parse(srv.URL)
 
-	err := svc.SendNtfy(
-		context.Background(), topicURL, "t", "m", "info",
-	)
+	err := send(svc, target)
 	if err == nil {
-		t.Fatal("expected error for 403 response")
+		t.Fatalf("expected error for %d response", status)
 	}
 
-	if !errors.Is(err, notify.ErrNtfyFailed) {
-		t.Errorf("error = %v, want ErrNtfyFailed", err)
+	if !errors.Is(err, wantErr) {
+		t.Errorf("error = %v, want %v", err, wantErr)
 	}
 }
 
+func sendNtfyInfo(
+	svc *notify.Service, target *url.URL,
+) error {
+	return svc.SendNtfy(
+		context.Background(), target, "t", "m", prioInfo,
+	)
+}
+
+func sendSlackInfo(
+	svc *notify.Service, target *url.URL,
+) error {
+	return svc.SendSlack(
+		context.Background(), target, "t", "m", prioInfo,
+	)
+}
+
+func TestSendNtfyClientError(t *testing.T) {
+	t.Parallel()
+
+	assertSendStatusError(
+		t, http.StatusForbidden,
+		notify.ErrNtfyFailed, sendNtfyInfo,
+	)
+}
+
 func TestSendNtfyServerError(t *testing.T) {
 	t.Parallel()
 
-	srv := httptest.NewServer(
-		http.HandlerFunc(
-			func(w http.ResponseWriter, _ *http.Request) {
-				w.WriteHeader(http.StatusInternalServerError)
-			}),
+	assertSendStatusError(
+		t, http.StatusInternalServerError,
+		notify.ErrNtfyFailed, sendNtfyInfo,
 	)
-	defer srv.Close()
-
-	svc := notify.NewTestService(srv.Client().Transport)
-	topicURL, _ := url.Parse(srv.URL)
-
-	err := svc.SendNtfy(
-		context.Background(), topicURL, "t", "m", "info",
-	)
-	if err == nil {
-		t.Fatal("expected error for 500 response")
-	}
-
-	if !errors.Is(err, notify.ErrNtfyFailed) {
-		t.Errorf("error = %v, want ErrNtfyFailed", err)
-	}
 }
 
 func TestSendNtfySuccess(t *testing.T) {
@@ -550,11 +577,11 @@ func TestSendSlackAllColors(t *testing.T) {
 		priority string
 		want     string
 	}{
-		{"error", colorError},
-		{"warning", colorWarning},
-		{"success", colorSuccess},
-		{"info", colorInfo},
-		{"unknown", colorDefault},
+		{prioError, colorError},
+		{prioWarning, colorWarning},
+		{prioSuccess, colorSuccess},
+		{prioInfo, colorInfo},
+		{prioUnknown, colorDefault},
 	}
 
 	for _, tc := range colors {
@@ -606,53 +633,19 @@ func TestSendSlackAllColors(t *testing.T) {
 func TestSendSlackClientError(t *testing.T) {
 	t.Parallel()
 
-	srv := httptest.NewServer(
-		http.HandlerFunc(
-			func(w http.ResponseWriter, _ *http.Request) {
-				w.WriteHeader(http.StatusBadRequest)
-			}),
+	assertSendStatusError(
+		t, http.StatusBadRequest,
+		notify.ErrSlackFailed, sendSlackInfo,
 	)
-	defer srv.Close()
-
-	svc := notify.NewTestService(srv.Client().Transport)
-	webhookURL, _ := url.Parse(srv.URL)
-
-	err := svc.SendSlack(
-		context.Background(), webhookURL, "t", "m", "info",
-	)
-	if err == nil {
-		t.Fatal("expected error for 400 response")
-	}
-
-	if !errors.Is(err, notify.ErrSlackFailed) {
-		t.Errorf("error = %v, want ErrSlackFailed", err)
-	}
 }
 
 func TestSendSlackServerError(t *testing.T) {
 	t.Parallel()
 
-	srv := httptest.NewServer(
-		http.HandlerFunc(
-			func(w http.ResponseWriter, _ *http.Request) {
-				w.WriteHeader(http.StatusBadGateway)
-			}),
+	assertSendStatusError(
+		t, http.StatusBadGateway,
+		notify.ErrSlackFailed, sendSlackInfo,
 	)
-	defer srv.Close()
-
-	svc := notify.NewTestService(srv.Client().Transport)
-	webhookURL, _ := url.Parse(srv.URL)
-
-	err := svc.SendSlack(
-		context.Background(), webhookURL, "t", "m", "error",
-	)
-	if err == nil {
-		t.Fatal("expected error for 502 response")
-	}
-
-	if !errors.Is(err, notify.ErrSlackFailed) {
-		t.Errorf("error = %v, want ErrSlackFailed", err)
-	}
 }
 
 func TestSendSlackNetworkError(t *testing.T) {
@@ -977,74 +970,62 @@ func TestSendNotificationMattermostOnly(t *testing.T) {
 	}
 }
 
-func TestSendNotificationNtfyError(t *testing.T) {
-	t.Parallel()
+// assertSendNotificationTolerates verifies SendNotification
+// neither panics nor blocks when the endpoint configured by
+// setURL responds with status.
+func assertSendNotificationTolerates(
+	t *testing.T,
+	status int,
+	priority string,
+	setURL func(*notify.Service, *url.URL),
+) {
+	t.Helper()
 
 	srv := httptest.NewServer(
 		http.HandlerFunc(
 			func(w http.ResponseWriter, _ *http.Request) {
-				w.WriteHeader(http.StatusInternalServerError)
+				w.WriteHeader(status)
 			}),
 	)
 	defer srv.Close()
 
-	ntfyURL, _ := url.Parse(srv.URL)
+	target, _ := url.Parse(srv.URL)
 
 	svc := notify.NewTestService(http.DefaultTransport)
-	svc.SetNtfyURL(ntfyURL)
+	setURL(svc, target)
 
-	// Should not panic or block.
 	svc.SendNotification(
-		context.Background(), "t", "m", "error",
+		context.Background(), "t", "m", priority,
 	)
 
 	time.Sleep(100 * time.Millisecond)
 }
 
+func TestSendNotificationNtfyError(t *testing.T) {
+	t.Parallel()
+
+	assertSendNotificationTolerates(
+		t, http.StatusInternalServerError, prioError,
+		(*notify.Service).SetNtfyURL,
+	)
+}
+
 func TestSendNotificationSlackError(t *testing.T) {
 	t.Parallel()
 
-	srv := httptest.NewServer(
-		http.HandlerFunc(
-			func(w http.ResponseWriter, _ *http.Request) {
-				w.WriteHeader(http.StatusForbidden)
-			}),
+	assertSendNotificationTolerates(
+		t, http.StatusForbidden, prioError,
+		(*notify.Service).SetSlackWebhookURL,
 	)
-	defer srv.Close()
-
-	slackURL, _ := url.Parse(srv.URL)
-
-	svc := notify.NewTestService(http.DefaultTransport)
-	svc.SetSlackWebhookURL(slackURL)
-
-	svc.SendNotification(
-		context.Background(), "t", "m", "error",
-	)
-
-	time.Sleep(100 * time.Millisecond)
 }
 
 func TestSendNotificationMattermostError(t *testing.T) {
 	t.Parallel()
 
-	srv := httptest.NewServer(
-		http.HandlerFunc(
-			func(w http.ResponseWriter, _ *http.Request) {
-				w.WriteHeader(http.StatusBadGateway)
-			}),
+	assertSendNotificationTolerates(
+		t, http.StatusBadGateway, prioWarning,
+		(*notify.Service).SetMattermostWebhookURL,
 	)
-	defer srv.Close()
-
-	mmURL, _ := url.Parse(srv.URL)
-
-	svc := notify.NewTestService(http.DefaultTransport)
-	svc.SetMattermostWebhookURL(mmURL)
-
-	svc.SendNotification(
-		context.Background(), "t", "m", "warning",
-	)
-
-	time.Sleep(100 * time.Millisecond)
 }
 
 // ── SlackPayload JSON marshaling ──────────────────────────

internal/notify/history_test.go

@@ -29,14 +29,14 @@ func TestAlertHistoryAddAndRecent(t *testing.T) {
 		Timestamp: now.Add(-2 * time.Minute),
 		Title:     "first",
 		Message:   "msg1",
-		Priority:  "info",
+		Priority:  prioInfo,
 	})
 
 	h.Add(notify.AlertEntry{
 		Timestamp: now.Add(-1 * time.Minute),
 		Title:     "second",
 		Message:   "msg2",
-		Priority:  "warning",
+		Priority:  prioWarning,
 	})
 
 	entries := h.Recent()

internal/notify/retry.go

@@ -69,7 +69,7 @@ func (rc RetryConfig) backoff(attempt int) time.Duration {
 	lo := raw * (1 - jitterFraction)
 	hi := raw * (1 + jitterFraction)
 
-	jittered := lo + rand.Float64()*(hi-lo) //nolint:gosec // jitter does not need crypto/rand
+	jittered := lo + rand.Float64()*(hi-lo) //nolint:gosec // jitter needs no crypto/rand
 
 	return time.Duration(jittered)
 }

internal/resolver/dns_client.go

@@ -7,8 +7,8 @@ import (
 	"github.com/miekg/dns"
 )
 
-// DNSClient abstracts DNS wire-protocol exchanges over a single
-// transport, letting the resolver switch between UDP and TCP.
+// DNSClient abstracts DNS wire-protocol exchanges so the resolver
+// can be tested without hitting real nameservers.
 type DNSClient interface {
 	ExchangeContext(
 		ctx context.Context,

internal/resolver/resolver.go

@@ -67,4 +67,17 @@ func NewFromLogger(log *slog.Logger) *Resolver {
 	}
 }
 
+// NewFromLoggerWithClient creates a Resolver with a custom DNS
+// client, useful for testing with mock DNS responses.
+func NewFromLoggerWithClient(
+	log *slog.Logger,
+	client DNSClient,
+) *Resolver {
+	return &Resolver{
+		log:    log,
+		client: client,
+		tcp:    client,
+	}
+}
+
 // Method implementations are in iterative.go.

internal/resolver/resolver_test.go

@@ -10,6 +10,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/miekg/dns"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
@@ -623,41 +624,58 @@ func TestQueryAllNameservers_ContextCanceled(t *testing.T) {
 }
 
 // ----------------------------------------------------------------
-// Unreachable nameserver tests
+// Timeout tests
 // ----------------------------------------------------------------
 
-func TestQueryNameserverIP_UnreachableServer(t *testing.T) {
+func TestQueryNameserverIP_Timeout(t *testing.T) {
 	t.Parallel()
 
-	r := newTestResolver(t)
+	log := slog.New(slog.NewTextHandler(
+		os.Stderr,
+		&slog.HandlerOptions{Level: slog.LevelDebug},
+	))
+
+	r := resolver.NewFromLoggerWithClient(
+		log, &timeoutClient{},
+	)
 
 	ctx, cancel := context.WithTimeout(
 		context.Background(), 10*time.Second,
 	)
 	t.Cleanup(cancel)
 
-	// 192.0.2.1 is an RFC 5737 documentation address: no
-	// nameserver can exist there. Depending on the network
-	// path the queries either time out (silent drop) or fail
-	// fast (ICMP unreachable), so accept any non-OK status;
-	// the resolver must return a classified response with no
-	// records rather than an error or a hang.
+	// Query any IP — the client always returns a timeout error.
 	resp, err := r.QueryNameserverIP(
 		ctx, "unreachable.test.", "192.0.2.1",
 		"example.com",
 	)
 	require.NoError(t, err)
 
-	assert.NotEqual(t, resolver.StatusOK, resp.Status)
-
-	totalRecords := 0
-	for _, values := range resp.Records {
-		totalRecords += len(values)
-	}
-
-	assert.Zero(t, totalRecords)
+	assert.Equal(t, resolver.StatusTimeout, resp.Status)
+	assert.NotEmpty(t, resp.Error)
 }
 
+// timeoutClient simulates DNS timeout errors for testing.
+type timeoutClient struct{}
+
+func (c *timeoutClient) ExchangeContext(
+	_ context.Context,
+	_ *dns.Msg,
+	_ string,
+) (*dns.Msg, time.Duration, error) {
+	return nil, 0, &net.OpError{
+		Op:  "read",
+		Net: "udp",
+		Err: &timeoutError{},
+	}
+}
+
+type timeoutError struct{}
+
+func (e *timeoutError) Error() string   { return "i/o timeout" }
+func (e *timeoutError) Timeout() bool   { return true }
+func (e *timeoutError) Temporary() bool { return true }
+
 func TestResolveIPAddresses_ContextCanceled(t *testing.T) {
 	t.Parallel()
 

internal/state/state_test.go

@@ -13,6 +13,16 @@ import (
 
 const testHostname = "www.example.com"
 
+// Shared fixture values used across tests.
+const (
+	testNS1     = "ns1.example.com."
+	testNS2     = "ns2.example.com."
+	testAltNS1  = "ns1.test.com."
+	testIPv4    = "93.184.216.34"
+	testIP      = "1.2.3.4"
+	statusError = "error"
+)
+
 // populateState fills a State with representative test data across all categories.
 func populateState(t *testing.T, s *state.State) {
 	t.Helper()
@@ -20,7 +30,7 @@ func populateState(t *testing.T, s *state.State) {
 	now := time.Now().UTC().Truncate(time.Second)
 
 	s.SetDomainState("example.com", &state.DomainState{
-		Nameservers: []string{"ns1.example.com.", "ns2.example.com."},
+		Nameservers: []string{testNS1, testNS2},
 		LastChecked: now,
 	})
 
@@ -31,17 +41,17 @@ func populateState(t *testing.T, s *state.State) {
 
 	s.SetHostnameState(testHostname, &state.HostnameState{
 		RecordsByNameserver: map[string]*state.NameserverRecordState{
-			"ns1.example.com.": {
+			testNS1: {
 				Records: map[string][]string{
-					"A":    {"93.184.216.34"},
+					"A":    {testIPv4},
 					"AAAA": {"2606:2800:220:1:248:1893:25c8:1946"},
 				},
 				Status:      "ok",
 				LastChecked: now,
 			},
-			"ns2.example.com.": {
+			testNS2: {
 				Records: map[string][]string{
-					"A": {"93.184.216.34"},
+					"A": {testIPv4},
 				},
 				Status:      "ok",
 				LastChecked: now,
@@ -152,13 +162,13 @@ func TestSaveLoadRoundTrip_Hostnames(t *testing.T) {
 func verifyNS1Records(t *testing.T, hn *state.HostnameState) {
 	t.Helper()
 
-	ns1, ok := hn.RecordsByNameserver["ns1.example.com."]
+	ns1, ok := hn.RecordsByNameserver[testNS1]
 	if !ok {
 		t.Fatal("missing nameserver ns1.example.com.")
 	}
 
 	aRecords := ns1.Records["A"]
-	if len(aRecords) != 1 || aRecords[0] != "93.184.216.34" {
+	if len(aRecords) != 1 || aRecords[0] != testIPv4 {
 		t.Errorf("ns1 A records: got %v", aRecords)
 	}
 
@@ -213,7 +223,8 @@ func TestSaveLoadRoundTrip_Ports(t *testing.T) {
 	}
 }
 
-// TestSaveLoadRoundTrip_Certificates verifies certificate data survives a save/load cycle.
+// TestSaveLoadRoundTrip_Certificates verifies certificate data
+// survives a save/load cycle.
 func TestSaveLoadRoundTrip_Certificates(t *testing.T) {
 	t.Parallel()
 
@@ -653,7 +664,7 @@ func TestDomainState_GetSet(t *testing.T) {
 
 	now := time.Now().UTC().Truncate(time.Second)
 	ds := &state.DomainState{
-		Nameservers: []string{"ns1.test.com."},
+		Nameservers: []string{testAltNS1},
 		LastChecked: now,
 	}
 
@@ -664,7 +675,7 @@ func TestDomainState_GetSet(t *testing.T) {
 		t.Fatal("expected true for existing domain")
 	}
 
-	if len(got.Nameservers) != 1 || got.Nameservers[0] != "ns1.test.com." {
+	if len(got.Nameservers) != 1 || got.Nameservers[0] != testAltNS1 {
 		t.Errorf("nameservers: got %v", got.Nameservers)
 	}
 
@@ -674,7 +685,7 @@ func TestDomainState_GetSet(t *testing.T) {
 
 	// Overwrite.
 	ds2 := &state.DomainState{
-		Nameservers: []string{"ns1.test.com.", "ns2.test.com."},
+		Nameservers: []string{testAltNS1, "ns2.test.com."},
 		LastChecked: now.Add(time.Hour),
 	}
 
@@ -704,8 +715,8 @@ func TestHostnameState_GetSet(t *testing.T) {
 	now := time.Now().UTC().Truncate(time.Second)
 	hs := &state.HostnameState{
 		RecordsByNameserver: map[string]*state.NameserverRecordState{
-			"ns1.example.com.": {
-				Records:     map[string][]string{"A": {"1.2.3.4"}},
+			testNS1: {
+				Records:     map[string][]string{"A": {testIP}},
 				Status:      "ok",
 				LastChecked: now,
 			},
@@ -720,7 +731,7 @@ func TestHostnameState_GetSet(t *testing.T) {
 		t.Fatal("expected true for existing hostname")
 	}
 
-	nsState, ok := got.RecordsByNameserver["ns1.example.com."]
+	nsState, ok := got.RecordsByNameserver[testNS1]
 	if !ok {
 		t.Fatal("missing nameserver entry")
 	}
@@ -730,7 +741,7 @@ func TestHostnameState_GetSet(t *testing.T) {
 	}
 
 	aRecords := nsState.Records["A"]
-	if len(aRecords) != 1 || aRecords[0] != "1.2.3.4" {
+	if len(aRecords) != 1 || aRecords[0] != testIP {
 		t.Errorf("A records: got %v", aRecords)
 	}
 }
@@ -869,7 +880,7 @@ func TestCertificateState_ErrorField(t *testing.T) {
 
 	now := time.Now().UTC().Truncate(time.Second)
 	cs := &state.CertificateState{
-		Status:      "error",
+		Status:      statusError,
 		Error:       "connection refused",
 		LastChecked: now,
 	}
@@ -893,8 +904,8 @@ func TestCertificateState_ErrorField(t *testing.T) {
 		t.Fatal("missing certificate after load")
 	}
 
-	if got.Status != "error" {
-		t.Errorf("status: got %q, want %q", got.Status, "error")
+	if got.Status != statusError {
+		t.Errorf("status: got %q, want %q", got.Status, statusError)
 	}
 
 	if got.Error != "connection refused" {
@@ -912,9 +923,9 @@ func TestHostnameState_ErrorField(t *testing.T) {
 	now := time.Now().UTC().Truncate(time.Second)
 	hs := &state.HostnameState{
 		RecordsByNameserver: map[string]*state.NameserverRecordState{
-			"ns1.example.com.": {
+			testNS1: {
 				Records:     nil,
-				Status:      "error",
+				Status:      statusError,
 				Error:       "SERVFAIL",
 				LastChecked: now,
 			},
@@ -941,9 +952,9 @@ func TestHostnameState_ErrorField(t *testing.T) {
 		t.Fatal("missing hostname after load")
 	}
 
-	nsState := got.RecordsByNameserver["ns1.example.com."]
-	if nsState.Status != "error" {
-		t.Errorf("status: got %q, want %q", nsState.Status, "error")
+	nsState := got.RecordsByNameserver[testNS1]
+	if nsState.Status != statusError {
+		t.Errorf("status: got %q, want %q", nsState.Status, statusError)
 	}
 
 	if nsState.Error != "SERVFAIL" {
@@ -1062,7 +1073,8 @@ func TestConcurrentGetSet(t *testing.T) {
 	wg.Wait()
 }
 
-// runConcurrentOps performs a series of get/set/delete operations for concurrency testing.
+// runConcurrentOps performs a series of get/set/delete
+// operations for concurrency testing.
 func runConcurrentOps(s *state.State, key string, now time.Time) {
 	const iterations = 50
 
@@ -1085,7 +1097,7 @@ func runConcurrentOps(s *state.State, key string, now time.Time) {
 		s.SetHostnameState(key+".example.com", &state.HostnameState{
 			RecordsByNameserver: map[string]*state.NameserverRecordState{
 				"ns1.test.": {
-					Records:     map[string][]string{"A": {"1.2.3.4"}},
+					Records:     map[string][]string{"A": {testIP}},
 					Status:      "ok",
 					LastChecked: now,
 				},

internal/watcher/watcher.go

@@ -26,6 +26,12 @@ const tlsPort = 443
 // hoursPerDay converts days to hours for duration calculations.
 const hoursPerDay = 24
 
+// Status values recorded for nameserver and certificate checks.
+const (
+	statusOK    = "ok"
+	statusError = "error"
+)
+
 // Params contains dependencies for Watcher.
 type Params struct {
 	fx.In
@@ -344,7 +350,7 @@ func buildHostnameState(
 	for ns, recs := range records {
 		hs.RecordsByNameserver[ns] = &state.NameserverRecordState{
 			Records:     recs,
-			Status:      "ok",
+			Status:      statusOK,
 			LastChecked: now,
 		}
 	}
@@ -402,7 +408,7 @@ func (w *Watcher) detectNSDisappearances(
 	current map[string]map[string][]string,
 ) {
 	for ns, prevNS := range prev.RecordsByNameserver {
-		if _, ok := current[ns]; ok || prevNS.Status != "ok" {
+		if _, ok := current[ns]; ok || prevNS.Status != statusOK {
 			continue
 		}
 
@@ -421,7 +427,7 @@ func (w *Watcher) detectNSDisappearances(
 
 	for ns := range current {
 		prevNS, ok := prev.RecordsByNameserver[ns]
-		if !ok || prevNS.Status != "error" {
+		if !ok || prevNS.Status != statusError {
 			continue
 		}
 
@@ -705,7 +711,7 @@ func (w *Watcher) handleTLSError(
 	now time.Time,
 	err error,
 ) {
-	if hasPrev && !w.firstRun && prev.Status == "ok" {
+	if hasPrev && !w.firstRun && prev.Status == statusOK {
 		msg := fmt.Sprintf(
 			"Host: %s\nIP: %s\nError: %s",
 			hostname, ip, err,
@@ -721,7 +727,7 @@ func (w *Watcher) handleTLSError(
 
 	w.state.SetCertificateState(
 		certKey, &state.CertificateState{
-			Status:      "error",
+			Status:      statusError,
 			Error:       err.Error(),
 			LastChecked: now,
 		},
@@ -748,7 +754,7 @@ func (w *Watcher) handleTLSSuccess(
 			Issuer:                  cert.Issuer,
 			NotAfter:                cert.NotAfter,
 			SubjectAlternativeNames: cert.SubjectAlternativeNames,
-			Status:                  "ok",
+			Status:                  statusOK,
 			LastChecked:             now,
 		},
 	)
@@ -760,7 +766,7 @@ func (w *Watcher) detectTLSChanges(
 	prev *state.CertificateState,
 	cert *tlscheck.CertificateInfo,
 ) {
-	if prev.Status == "error" {
+	if prev.Status == statusError {
 		msg := fmt.Sprintf(
 			"Host: %s\nIP: %s\nTLS recovered",
 			hostname, ip,

script/bootstrap

@@ -9,9 +9,9 @@ set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
-# Pinned versions, 2026-07-07 (same pins as the Dockerfile)
-# golangci-lint v2.10.1
-GOLANGCI_LINT_REF="github.com/golangci/golangci-lint/v2/cmd/golangci-lint@5d1e709b7be35cb2025444e19de266b056b7b7ee"
+# Pinned versions, 2026-08-07 (same pins as the Dockerfile)
+# golangci-lint v2.12.2
+GOLANGCI_LINT_REF="github.com/golangci/golangci-lint/v2/cmd/golangci-lint@c0d3ddc9cf3faa61a4e378e879ece580256d76e5"
 # goimports v0.42.0
 GOIMPORTS_REF="golang.org/x/tools/cmd/goimports@009367f5c17a8d4c45a961a3a509277190a9a6f0"