A collision is two places, not two spellings

checkResources compared paths as written, so ${dir:state}/server.env —
the same characters in every module, a different directory in each —
refused the first two placed modules that met. Paths are placed before
they are compared, under the default root, which keeps every real
collision: distinct modules' places are distinct under any one root,
and a module stating another's placed root is caught because a pathless
directory now owns its placed path in the comparison too.

internal/catalogue/dir_into_test.go

@@ -221,6 +221,28 @@ func TestPlaceIsValidatedAtTheManifest(t *testing.T) {
 	}
 }
 
+func TestTwoModulesPlacedRootsAreNoCollision(t *testing.T) {
+	a := Manifest{Module: "gitea", Resources: []map[string]any{
+		{"id": "state", "type": "directory", "place": "."},
+		{"id": "env", "type": "file", "path": "${dir:state}/server.env", "content": ""},
+	}}
+	b := Manifest{Module: "nextcloud", Resources: []map[string]any{
+		{"id": "state", "type": "directory", "place": "."},
+		{"id": "env", "type": "file", "path": "${dir:state}/server.env", "content": ""},
+	}}
+	if got := checkResources([]Manifest{a, b}); len(got) != 0 {
+		t.Fatalf("alike templates are different places; got %v", got)
+	}
+	// And the real collision is still caught: a module stating another's placed root.
+	c := Manifest{Module: "squatter", Resources: []map[string]any{
+		{"id": "nest", "type": "directory", "path": "/var/lib/gitea"},
+	}}
+	got := checkResources([]Manifest{a, c})
+	if len(got) != 1 || !strings.Contains(got[0], `"/var/lib/gitea"`) {
+		t.Fatalf("a stated path on a placed root collides; got %v", got)
+	}
+}
+
 func shallowCopy(resource map[string]any) map[string]any {
 	copied := map[string]any{}
 	for k, v := range resource {