diff --git a/backend/internal/checks/coverage_test.go b/backend/internal/checks/coverage_test.go
index e044e8cd..7b978686 100644
--- a/backend/internal/checks/coverage_test.go
+++ b/backend/internal/checks/coverage_test.go
@@ -49,7 +49,7 @@ var oracleSplit = []struct {
 	{"Mr. Smith went. He left.", []string{"Mr.", "Smith went.", "He left."}}, // naive over-split (known)
 	// U+001F (unit separator) is whitespace to Python (\s / str.isspace) but NOT to
 	// Go's unicode.IsSpace — isOracleSpace bridges the gap for oracle parity.
-	{"A.B.", []string{"A.", "B."}},
+	{"A.\x1fB.", []string{"A.", "B."}},
 }
 
 func TestSplitSentencesOracleParity(t *testing.T) {
@@ -100,7 +100,7 @@ func boevoyGate(minChars int) config.CoverageGate {
 // information separators U+001C–U+001F, which Python treats as whitespace (\s /
 // str.isspace) but Go's unicode.IsSpace does not — a real bit-parity gap (self-review).
 func TestOracleSpaceControlChars(t *testing.T) {
-	us := "" // U+001F unit separator (survives EPUB/PDF extraction)
+	us := "\x1f" // U+001F unit separator (survives EPUB/PDF extraction)
 	if got := splitSentences("A." + us + "B."); len(got) != 2 || got[0] != "A." || got[1] != "B." {
 		t.Fatalf("U+001F after a terminator must split like the oracle, got %#v", got)
 	}
diff --git a/backend/internal/checks/labelcandidates_test.go b/backend/internal/checks/labelcandidates_test.go
index 5b4ca8d5..6afe5ba5 100644
--- a/backend/internal/checks/labelcandidates_test.go
+++ b/backend/internal/checks/labelcandidates_test.go
@@ -33,7 +33,7 @@ func TestCheckerLabelsCandidates(t *testing.T) {
 		if l.Bucket != "chevron" {
 			continue
 		}
-		line := strings.TrimLeft(lineForLabel(l, units), " \t 　")
+		line := strings.TrimLeft(lineForLabel(l, units), " \t　")
 		rs := []rune(line)
 		base := chevronSpeechShapeCommaOnly(rs) && c.isSpokenChevronLine(line)
 		cand := chevronSpeechShape(rs) && c.isSpokenChevronLine(line)
@@ -76,7 +76,7 @@ func TestCheckerLabelsCandidates(t *testing.T) {
 		if l.Bucket != "em-dash" {
 			continue
 		}
-		line := strings.TrimLeft(lineForLabel(l, units), " \t 　")
+		line := strings.TrimLeft(lineForLabel(l, units), " \t　")
 		rs := []rune(line)
 		isDash := len(rs) > 0 && (rs[0] == '—' || rs[0] == '–' || rs[0] == '-')
 		attr := speechAttribution(line)
@@ -95,9 +95,10 @@ func TestCheckerLabelsCandidates(t *testing.T) {
 	for _, l := range loadJSONL(t, filepath.Join(labelsDir, "labels", "k2.jsonl")) {
 		tok := []rune(l.Token)
 		if len(tok) >= 3 && isAllLatinLetters(tok) && hasUpper(tok) {
-			if l.Label == "defect" {
+			switch l.Label {
+			case "defect":
 				capsDefect = append(capsDefect, l.Token)
-			} else if l.Label == "ok" {
+			case "ok":
 				capsOK = append(capsOK, l.Token)
 			}
 		}
diff --git a/backend/internal/checks/labelharness_test.go b/backend/internal/checks/labelharness_test.go
index 9e83ec52..e874ac2e 100644
--- a/backend/internal/checks/labelharness_test.go
+++ b/backend/internal/checks/labelharness_test.go
@@ -350,14 +350,14 @@ func measureK4(labels []labelRow, units map[string]corpusUnit, c *Checkers) (met
 	for _, l := range labels {
 		switch l.Bucket {
 		case "chevron":
-			line := strings.TrimLeft(lineForLabel(l, units), " \t 　")
+			line := strings.TrimLeft(lineForLabel(l, units), " \t　")
 			flagged := chevronSpeechShape([]rune(line)) && c.isSpokenChevronLine(line)
 			joinK4(&k4b, l.Speech, "spoken", flagged)
 		case "em-dash":
 			// k4_inverse (D39.39): a dash line whose ATTRIBUTION carries an inner-speech marker is a thought
 			// typeset as spoken — scoped to the attribution (matches production speechAttribution), not the
 			// whole line, so a spoken reply that merely mentions «про себя» is not flagged.
-			line := strings.TrimLeft(lineForLabel(l, units), " \t 　")
+			line := strings.TrimLeft(lineForLabel(l, units), " \t　")
 			rs := []rune(line)
 			isDash := len(rs) > 0 && (rs[0] == '—' || rs[0] == '–' || rs[0] == '-')
 			attr := speechAttribution(line)
@@ -375,7 +375,7 @@ func measureK4(labels []labelRow, units map[string]corpusUnit, c *Checkers) (met
 func measureK4a(labels []labelRow, units map[string]corpusUnit) metric {
 	var m metric
 	for _, l := range labels {
-		rs := []rune(strings.TrimLeft(lineForLabel(l, units), " \t 　"))
+		rs := []rune(strings.TrimLeft(lineForLabel(l, units), " \t　"))
 		defect := false
 		if len(rs) > 0 {
 			switch rs[0] {
diff --git a/backend/internal/miner/miner_alias.go b/backend/internal/miner/miner_alias.go
index dcf62dba..70c4a043 100644
--- a/backend/internal/miner/miner_alias.go
+++ b/backend/internal/miner/miner_alias.go
@@ -158,8 +158,7 @@ func clusterAlias(ident []aliasEdge, allSurfaces []string) [][]string {
 	for _, s := range allSurfaces {
 		parent[s] = s
 	}
-	var find func(string) string
-	find = func(x string) string {
+	find := func(x string) string {
 		for parent[x] != x {
 			parent[x] = parent[parent[x]]
 			x = parent[x]
diff --git a/backend/internal/pipeline/ratelimit_test.go b/backend/internal/pipeline/ratelimit_test.go
index 4bbfb235..0b8afec8 100644
--- a/backend/internal/pipeline/ratelimit_test.go
+++ b/backend/internal/pipeline/ratelimit_test.go
@@ -2,6 +2,7 @@ package pipeline
 
 import (
 	"context"
+	"errors"
 	"sync"
 	"sync/atomic"
 	"testing"
@@ -84,7 +85,7 @@ func TestRateGuardHonoursContextCancel(t *testing.T) {
 	cancel()
 	select {
 	case err := <-done:
-		if err != context.Canceled {
+		if !errors.Is(err, context.Canceled) {
 			t.Fatalf("blocked acquire on cancel = %v, want context.Canceled", err)
 		}
 	case <-time.After(time.Second):
diff --git a/backend/internal/pipeline/repair.go b/backend/internal/pipeline/repair.go
index 2c2682ca..189860b6 100644
--- a/backend/internal/pipeline/repair.go
+++ b/backend/internal/pipeline/repair.go
@@ -500,7 +500,7 @@ func classInvariantRestored(cls checks.RepairClass, c *checks.Checkers, original
 	case checks.RepairDC1Fractional:
 		// The halved duration must be gone AND the replacement must still state a duration: a reply that
 		// simply drops the time expression is a deletion, not a conversion.
-		return checks.FractionalUnitPresent(c, reply) == false && checks.MentionsHourWord(c, reply)
+		return !checks.FractionalUnitPresent(c, reply) && checks.MentionsHourWord(c, reply)
 	case checks.RepairDC1TimeUnits:
 		// The counted-hours class: assert the hours count POSITIVELY equals twice the source count. On the
 		// pair data as it stands this also rejects a correct repair phrased in a case form the hours table
diff --git a/backend/internal/pipeline/runner_memory_test.go b/backend/internal/pipeline/runner_memory_test.go
index dd430ad8..c48b7df7 100644
--- a/backend/internal/pipeline/runner_memory_test.go
+++ b/backend/internal/pipeline/runner_memory_test.go
@@ -284,7 +284,7 @@ func TestRunnerMemoryResnapshotOnApprovedChange(t *testing.T) {
 	// snapshot changes → a resume without --resnapshot must fail loud (F1: no silent
 	// divergent re-pay).
 	seedPath := filepath.Join(filepath.Dir(bookPath), "glossary-seed.yaml")
-	if err := os.WriteFile(seedPath, []byte(strings.Replace(suzukiSeed, "Судзуки", "Сузуки", -1)), 0o644); err != nil {
+	if err := os.WriteFile(seedPath, []byte(strings.ReplaceAll(suzukiSeed, "Судзуки", "Сузуки")), 0o644); err != nil {
 		t.Fatal(err)
 	}
 	r2 := newRunner(t, bookPath)