A tool runner is no longer restarted by a build of the engine: owned paths name the directory of every build, and a restart names its cause (issue 1966)

The tool runner's unit carries the paths modules own, for the holder of node-files. The engine's own
archive is unpacked into a place named for its build, so every engine replacement changed that word
and restarted the tool runner with nothing of it changed (novox 21:16, 22:25, 22:38 on 2026-11-09).
A resource unpacked into a place named for its build now owns the directory holding every build.
The restart line now names the unit's directive, word and key that differ, never a value.

Claude-Session: https://claude.ai/code/session_01JG73KEq4zoDfM9WtYpcQgZ

internal/compose/resolution/seat_paths.go

@@ -26,7 +26,7 @@ func declaredPaths(m mcat.Manifest) map[string]bool {
 	}
 	for _, r := range m.Resources {
 		if p, ok := r["path"].(string); ok && strings.HasPrefix(p, "/") {
-			out[path.Clean(p)] = true
+			out[path.Clean(versionedPlaceOwner(r, p))] = true
 		}
 	}
 	for _, f := range m.Facts {
@@ -123,3 +123,18 @@ func seatPathsOnMachine(modules []mcat.Manifest) []string {
 	}
 	return problems
 }
+
+// versionedPlaceOwner is the path a resource owns: its own, unless the resource is an archive unpacked into a place named
+// for its build (the artifact's digest, short: `.../versions/<version>`, catalogue `${version}`), whose owner is the
+// directory holding every such place, because the place changes with each build and the owned paths are an input of the
+// tool runner's unit (the holder of node-files reads them at its start): a build of the engine itself renamed its place
+// and restarted the tool runner, with nothing of the tool runner changed (issue 1966).
+func versionedPlaceOwner(r map[string]any, p string) string {
+	digest, _ := r["digest"].(string)
+	version := strings.TrimPrefix(digest, "sha256:")
+	base := path.Base(path.Clean(p))
+	if r["type"] == "archive" && len(base) >= 8 && strings.HasPrefix(version, base) {
+		return path.Dir(path.Clean(p))
+	}
+	return p
+}

internal/compose/resolution/seat_paths_test.go

@@ -54,3 +54,27 @@ func TestAnUplinkDeclaringTheResolverFileAsAResourceIsRefusedBesideTheResolver(t
 		t.Errorf("the uplink's holder renders %v beside the resolver", got.Facts)
 	}
 }
+
+// The paths a module owns do not change with its build (issue 1966): the holder of node-files is told them in an
+// environment word of the tool runner's unit, so a place named for each build moved with every build of its module and
+// restarted the tool runner each time.
+func TestAPathNamedForABuildIsOwnedAsTheDirectoryHoldingEveryBuild(t *testing.T) {
+	digest := "sha256:" + strings.Repeat("ab12", 16)
+	for _, row := range []struct {
+		name string
+		res  map[string]any
+		owns string
+	}{
+		{"a build's own place", map[string]any{"id": "next", "type": "archive", "digest": digest, "path": "/usr/lib/x/versions/ab12ab12ab12"}, "/usr/lib/x/versions"},
+		{"another build's place", map[string]any{"id": "next", "type": "archive", "digest": "sha256:" + strings.Repeat("cd34", 16), "path": "/usr/lib/x/versions/cd34cd34cd34"}, "/usr/lib/x/versions"},
+		{"a fixed place", map[string]any{"id": "app", "type": "archive", "digest": digest, "path": "/opt/app"}, "/opt/app"},
+		{"a file", map[string]any{"id": "f", "type": "file", "path": "/etc/f"}, "/etc/f"},
+	} {
+		t.Run(row.name, func(t *testing.T) {
+			got := DeclaredPaths(mcat.Manifest{Module: "m", Resources: []map[string]any{row.res}})
+			if len(got) != 1 || got[0] != row.owns {
+				t.Fatalf("owns %v, want [%s]", got, row.owns)
+			}
+		})
+	}
+}