Pin apt child process locale in UpdatesCollector

internal/collector/updates.go

@@ -104,7 +104,18 @@ func (c *UpdatesCollector) Collect(ctx context.Context) (Updates, error) {
 	defer cancel()
 
 	cmd := exec.CommandContext(ctx, c.aptPath, "list", "--upgradable")
-	cmd.Env = append(os.Environ(), "DEBIAN_FRONTEND=noninteractive")
+	// apt localises its output via gettext; the parser above matches the
+	// English strings, so pin the locale rather than inheriting the
+	// operator's. LC_ALL beats LANG and LANGUAGE, but all three are set so
+	// no inherited value can leak through. PATH must be preserved because
+	// aptPath is typically the bare string "apt", resolved via PATH.
+	cmd.Env = []string{
+		"LC_ALL=C",
+		"LANG=C",
+		"LANGUAGE=",
+		"DEBIAN_FRONTEND=noninteractive",
+		"PATH=" + os.Getenv("PATH"),
+	}
 	out, err := cmd.Output()
 	if err != nil {
 		return Updates{}, fmt.Errorf("run apt list --upgradable: %w", err)

internal/collector/updates_test.go

@@ -2,8 +2,10 @@ package collector
 
 import (
 	"context"
+	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 	"time"
 )
@@ -92,3 +94,48 @@ func TestUpdatesCollector_Collect_StalenessDetection(t *testing.T) {
 		t.Fatalf("expected Stale=true for a 48h old cache with a 6h threshold, got %+v", updates)
 	}
 }
+
+func TestUpdatesCollector_Collect_PinsLocale(t *testing.T) {
+	dir := t.TempDir()
+	envFile := filepath.Join(dir, "env.out")
+	aptStub := writeFakeVcgencmd(t, dir, "fake-apt", fmt.Sprintf("env > %q", envFile))
+
+	c := &UpdatesCollector{
+		aptPath:  aptStub,
+		listsDir: filepath.Join(dir, "missing-lists"),
+		now:      time.Now,
+	}
+
+	if _, err := c.Collect(context.Background()); err != nil {
+		t.Fatalf("Collect: %v", err)
+	}
+
+	out, err := os.ReadFile(envFile)
+	if err != nil {
+		t.Fatalf("read captured child environment: %v", err)
+	}
+
+	env := map[string]string{}
+	for _, line := range strings.Split(strings.TrimSpace(string(out)), "\n") {
+		k, v, ok := strings.Cut(line, "=")
+		if !ok {
+			continue
+		}
+		env[k] = v
+	}
+
+	if env["LC_ALL"] != "C" {
+		t.Errorf("LC_ALL = %q, want C", env["LC_ALL"])
+	}
+	if env["LANG"] != "C" {
+		t.Errorf("LANG = %q, want C", env["LANG"])
+	}
+	if v, ok := env["LANGUAGE"]; ok && v != "" {
+		t.Errorf("LANGUAGE = %q, want empty", v)
+	}
+	// Regression guard: PATH must survive, otherwise "apt" (a bare command
+	// name, resolved via PATH) would not be executable at all.
+	if env["PATH"] == "" {
+		t.Error("PATH not present in child environment; apt would not be resolvable")
+	}
+}