test(diary): config, channels, rotation, redaction and slogtest

- config rules name their key; env strings overlay defaults; D-08 defaults
- component floors, verbosity 1-3, quiet on the console only
- daily rotation, retention, 0640 files, unwritable dir, lazy open, path confinement
- redaction on every driver, console control-character stripping and prefix
- loggers before Setup, Reset, HideOnTTY, 100 concurrent writers
- testing/slogtest for the console handler and the JSON pipeline
- sunscreen InstallDefault still installs a redacting logfmt handler

modules/sunscreen/sunscreen_test.go

@@ -142,3 +142,42 @@ func TestInstallDefault(t *testing.T) {
 		t.Fatalf("default logger output:\n%s", out)
 	}
 }
+
+// TestInstallDefaultUnchanged: InstallDefault, the compatibility entry
+// point that generated applications no longer call, still installs a
+// redacting logfmt TextHandler on the given writer, and each call replaces
+// the previous default instead of wrapping it.
+func TestInstallDefaultUnchanged(t *testing.T) {
+	prev := slog.Default()
+	prevFlags, prevWriter := log.Flags(), log.Writer()
+	t.Cleanup(func() {
+		slog.SetDefault(prev)
+		log.SetFlags(prevFlags)
+		log.SetOutput(prevWriter)
+	})
+	var first, second bytes.Buffer
+	InstallDefault(&first)
+	InstallDefault(&second)
+	slog.Debug("below the default level", "token", nested)
+	slog.Info("payment for Bearer "+bearer, "api_key", apiKey, slog.Group("g", "Password", passwd))
+	if first.Len() != 0 {
+		t.Fatalf("the replaced default still receives records:\n%s", first.String())
+	}
+	out := second.String()
+	if strings.Count(out, "\n") != 1 {
+		t.Fatalf("want exactly one line (info level, debug dropped):\n%s", out)
+	}
+	for _, want := range []string{"time=", " level=INFO ", `msg="payment for Bearer [REDACTED]"`, "api_key=[REDACTED]", "g.Password=[REDACTED]"} {
+		if !strings.Contains(out, want) {
+			t.Errorf("default output lacks %q:\n%s", want, out)
+		}
+	}
+	for _, secret := range []string{bearer, apiKey, passwd, nested} {
+		if strings.Contains(out, secret) {
+			t.Errorf("default output leaks %q:\n%s", secret, out)
+		}
+	}
+	if strings.HasPrefix(strings.TrimSpace(out), "{") {
+		t.Errorf("default output is JSON, want logfmt:\n%s", out)
+	}
+}