M2: ai claude and codex CLI backends with selector

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/ai/backend_test.go

@@ -0,0 +1,47 @@
+package ai
+
+import (
+	"slices"
+	"testing"
+)
+
+func TestNewBackendSelector(t *testing.T) {
+	for _, name := range []string{"", "claude"} {
+		b, err := NewBackend(name)
+		if err != nil {
+			t.Fatalf("NewBackend(%q): %v", name, err)
+		}
+		if b.Name() != "claude" {
+			t.Fatalf("NewBackend(%q) name = %q", name, b.Name())
+		}
+	}
+	b, err := NewBackend("codex")
+	if err != nil || b.Name() != "codex" {
+		t.Fatalf("codex backend: %v / %q", err, b.Name())
+	}
+	if _, err := NewBackend("bogus"); err == nil {
+		t.Fatal("unknown backend should error")
+	}
+}
+
+func TestClaudeArgs(t *testing.T) {
+	want := []string{"--print", "--tools", "", "--no-session-persistence", "--output-format", "text"}
+	if got := newClaudeBackend().args; !slices.Equal(got, want) {
+		t.Fatalf("claude args = %v want %v", got, want)
+	}
+}
+
+func TestCodexArgsCarryOutfileAndStdinMarker(t *testing.T) {
+	got := newCodexBackend().args("/tmp/out.txt")
+	if got[len(got)-1] != "-" {
+		t.Fatalf("codex args must end with stdin marker '-', got %v", got)
+	}
+	if !slices.Contains(got, "-o") || !slices.Contains(got, "/tmp/out.txt") {
+		t.Fatalf("codex args must include -o /tmp/out.txt, got %v", got)
+	}
+	for _, want := range []string{"exec", "--ignore-user-config", "--ignore-rules", "read-only", "never"} {
+		if !slices.Contains(got, want) {
+			t.Fatalf("codex args missing %q, got %v", want, got)
+		}
+	}
+}