fix!(policy/checker): make List and-like

This has the potential to break user configs.

Anubis lets you stack multiple checks at once with blocks like this:

```yaml
name: allow-prometheus
action: ALLOW
user_agent_regex: ^prometheus-probe$
remote_addresses:
  - 192.168.2.0/24
```

Previously, this only returned ALLOW if _any one_ of the conditions
matched. This behaviour has changed to only return ALLOW if _all_ of the
conditions match.

I have marked this as a potentially breaking change because I'm
absolutely certain that someone is relying on this behaviour due to
spacebar heating. If this bites you, please let me know ASAP.

Signed-off-by: Xe Iaso <me@xeiaso.net>
Assisted-by: GPT-OSS 120b on local hardware

lib/policy/checker/checker.go

@@ -16,18 +16,26 @@ type Impl interface {
 
 type List []Impl
 
+// Check runs each checker in the list against the request.
+// It returns true only if *all* checkers return true (AND semantics).
+// If any checker returns an error, the function returns false and the error.
 func (l List) Check(r *http.Request) (bool, error) {
+	// Assume success until a checker says otherwise.
+	allOk := true
 	for _, c := range l {
 		ok, err := c.Check(r)
 		if err != nil {
-			return ok, err
+			// Propagate the error; overall result is false.
+			return false, err
 		}
-		if ok {
-			return ok, nil
+		if !ok {
+			// One false means the combined result is false. Short-circuit
+			// so we don't waste time.
+			allOk = false
+			break
 		}
 	}
-
-	return false, nil
+	return allOk, nil
 }
 
 func (l List) Hash() string {

lib/policy/checker/checker_test.go

@@ -0,0 +1,57 @@
+package checker
+
+import (
+	"errors"
+	"net/http"
+	"testing"
+)
+
+// Mock implements the Impl interface for testing.
+type Mock struct {
+	result bool
+	err    error
+	hash   string
+}
+
+func (m Mock) Check(r *http.Request) (bool, error) { return m.result, m.err }
+func (m Mock) Hash() string                        { return m.hash }
+
+func TestListCheck_AndSemantics(t *testing.T) {
+	req, _ := http.NewRequest(http.MethodGet, "http://example.com", nil)
+
+	tests := []struct {
+		name    string
+		list    List
+		want    bool
+		wantErr bool
+	}{
+		{
+			name: "all true",
+			list: List{Mock{true, nil, "a"}, Mock{true, nil, "b"}},
+			want: true,
+		},
+		{
+			name: "one false",
+			list: List{Mock{true, nil, "a"}, Mock{false, nil, "b"}},
+			want: false,
+		},
+		{
+			name:    "error propagates",
+			list:    List{Mock{true, nil, "a"}, Mock{true, errors.New("boom"), "b"}},
+			want:    false,
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := tt.list.Check(req)
+			if (err != nil) != tt.wantErr {
+				t.Fatalf("unexpected error state: %v", err)
+			}
+			if got != tt.want {
+				t.Fatalf("expected %v, got %v", tt.want, got)
+			}
+		})
+	}
+}