feat: scaffold codespace backend

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

internal/workspace/path_test.go

@@ -0,0 +1,31 @@
+package workspace
+
+import (
+	"testing"
+)
+
+func TestValidIDAcceptsSafeSegments(t *testing.T) {
+	valid := []string{"user1", "project-A", "project_A", "project.1"}
+	for _, id := range valid {
+		if !ValidID(id) {
+			t.Errorf("expected ValidID(%q) to be true", id)
+		}
+	}
+}
+
+func TestValidIDRejectsUnsafeSegments(t *testing.T) {
+	invalid := []string{"", ".", "..", "/tmp/x", "../x", "a/b", "a b", "中文", "*"}
+	for _, id := range invalid {
+		if ValidID(id) {
+			t.Errorf("expected ValidID(%q) to be false", id)
+		}
+	}
+}
+
+func TestRootForUsesConfiguredRoot(t *testing.T) {
+	got := RootFor("/tmp/workspaces", "user1")
+	want := "/tmp/workspaces/user1"
+	if got != want {
+		t.Errorf("RootFor = %q, want %q", got, want)
+	}
+}