A-342 engine-node-env: every process runs with its node's name as MESH_NODE

The apply gives each process the declaration's For as MESH_NODE beside its own env, so a process that reads MESH_NODE (mesh-sdk, the zfs follower's writer and its node-service-manager calls) names its node.

Builds: design 47 G A-342

Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h

internal/apply/apply.go

@@ -785,7 +785,7 @@ func applyScoped(
 	// change one apply late, and never misses it.
 	// And one patience with the artifact store for the whole apply (novox/hq issue 291): a fetch it
 	// does not answer during a maintenance window waits for the window instead of failing.
-	in := inputs{declares: map[string]string{}, known: &known, windows: windows, away: newStoreAway(windows, log),
+	in := inputs{node: d.For, declares: map[string]string{}, known: &known, windows: windows, away: newStoreAway(windows, log),
 		groups: wanted, handed: handed}
 	// Where nothing is placed or mounted from, judged before anything is applied (novox/hq issue 339), and
 	// which declared directories were already here: one this apply makes is the mesh's, one found may not be.
@@ -1625,7 +1625,7 @@ func applyOne(ctx context.Context, sys system.System, r declaration.Resource, ru
 		if err != nil {
 			return begin(r), err
 		}
-		return applyProcess(ctx, res, run, changed, previous, held, in.away)
+		return applyProcess(ctx, withNode(res, in.node), run, changed, previous, held, in.away)
 	case *declaration.Action:
 		return applyAction(ctx, res, run)
 	case *declaration.Network:
@@ -2816,6 +2816,9 @@ type inputs struct {
 	// fetched is every archive's and process's bytes this apply fetched before anything was replaced (fetchFirst), each
 	// taken by its applier once (artifact).
 	fetched map[string]fetchedArtifact
+	// node is the node's own name, the declaration's For: every process runs with it as MESH_NODE beside its own env
+	// (design 47 G A-342). Empty where the declaration names none (the first node's carried bundle).
+	node string
 }
 
 // fileDigest is what a file the container reads holds, by digest.

internal/apply/filled.go

@@ -95,7 +95,7 @@ func WriteFilledWith(
 			"yet taken (%s), so nothing was written", path, held.Why)}
 	}
 
-	in := inputs{declares: map[string]string{}, known: &known, windows: windows, away: newStoreAway(windows, log),
+	in := inputs{node: d.For, declares: map[string]string{}, known: &known, windows: windows, away: newStoreAway(windows, log),
 		groups: groupsWanted(d.Resources), handed: Handed{}}
 	in.refused = refusedPlaces(d.Resources)
 	in.agentHomes = rootNeverHomes(d)

internal/apply/process.go

@@ -274,6 +274,25 @@ func applyProcess(ctx context.Context, r *declaration.Process, run Runner,
 	return out, nil
 }
 
+// NodeEnv is the variable every process the node-engine runs reads its node's name from (design 47 G A-342), the one
+// mesh-sdk reads (MESH_NODE).
+const NodeEnv = "MESH_NODE"
+
+// withNode is the process as it runs on node: its own env with NodeEnv beside it (design 47 G A-342). The validator
+// refuses a resource that sets it, so the mesh's value is the only one; with no node named the process is as declared.
+func withNode(r *declaration.Process, node string) *declaration.Process {
+	if node == "" {
+		return r
+	}
+	p := *r
+	p.Env = make(map[string]string, len(r.Env)+1)
+	for k, v := range r.Env {
+		p.Env[k] = v
+	}
+	p.Env[NodeEnv] = node
+	return &p
+}
+
 // unitFor is the unit the mesh writes for a daemon.
 //
 // **Generated whole and never edited in place**, the same rule as every other managed file: an

internal/apply/process_test.go

@@ -319,11 +319,17 @@ func TestAProcessAppliedAgainIsUnchangedAndNotRestarted(t *testing.T) {
 	}
 	d := declare(t, `{"id":"node-tools.runtime","type":"process","name":"node-tools","source":"`+serving(t, body)+
 		`","digest":"`+digest+`","run":["node","main.js"],"env":{"MESH_TOOL_MODULES":"a=/x/index.js"}}`)
+	d.For = "anchor"
 
 	first, state, err := Apply(context.Background(), archHost(t), d, store.State{}, store.OriginDeclared, run, nil, nil)
 	if err != nil {
 		t.Fatal(err)
 	}
+	// Design 47 G A-342: the process runs with its node's name as MESH_NODE beside its own env.
+	if b, err := os.ReadFile(filepath.Join(units, "node-tools.service")); err != nil || !strings.Contains(string(b), `Environment="MESH_NODE=anchor"`) ||
+		!strings.Contains(string(b), `Environment="MESH_TOOL_MODULES=`) {
+		t.Errorf("the unit does not carry the node's name beside its env (%v):\n%s", err, b)
+	}
 	if o := outcomeOf(first, "node-tools.runtime"); o.Action != "created" {
 		t.Fatalf("first apply: %+v, want created", o)
 	}
@@ -360,6 +366,7 @@ func TestAProcessAppliedAgainIsUnchangedAndNotRestarted(t *testing.T) {
 	// An input of its unit that differs restarts it, and the line says which (issue 1966).
 	changed := declare(t, `{"id":"node-tools.runtime","type":"process","name":"node-tools","source":"`+serving(t, body)+
 		`","digest":"`+digest+`","run":["node","main.js"],"env":{"MESH_TOOL_MODULES":"a=/x/index.js,b=/y/index.js"}}`)
+	changed.For = "anchor"
 	fourth, _, err := Apply(context.Background(), archHost(t), changed, state, store.OriginDeclared, run, nil, nil)
 	if err != nil {
 		t.Fatal(err)