Something answered on this machine is still bound

A binding was skipped when the provider turned out to be on the same node,
reasoning that a file saying "it is on this node" is a fact nobody needs. That
is right about the location and wrong about everything beside it: a binding
also carries what the provider said a consumer must know, which is the port,
and a consumer cannot invent that.

A build machine sharing a node with the registry it pushes to sat in a loop
saying it could not read its own binding. Nothing was wrong with the machine,
the module, the credential or the provision — the file was never written, and
the absence looked exactly like a mistake in the module.

The original intent is kept where it was right: a provision whose provider said
nothing a consumer must know is still not written. A shell is answered here and
there is nothing to say about it. A registry is answered here and the port is
still unguessable.

The address is this machine's name on the private network, or loopback when it
has none — a machine off the network still reaches itself, and a name nothing
resolves is worse than an address that always works.

internal/catalogue/declaration.go

@@ -193,10 +193,22 @@ func (r Resolution) Declaration(with Rendering) ([]map[string]any, error) {
 				}
 			}
 			if found == nil {
-				// Bound to something answered on this machine rather than from the mesh. Nothing
-				// to write: the answer is here, and a file saying "it is on this node" would be
-				// a fact nobody needs and one more thing to keep true.
-				continue
+				// Answered on this same machine rather than from elsewhere in the mesh.
+				//
+				// **Still written.** It used to be skipped, reasoning that "it is on this node"
+				// is a fact nobody needs — and that is true of the *location* and false of
+				// everything beside it. A binding also carries what the provider said a consumer
+				// must know, which is the port; a consumer cannot invent that, and got an absent
+				// file with no explanation. A build machine sharing a node with the registry it
+				// pushes to sat in a loop saying it could not read its own binding.
+				here := here(r, to)
+				if here == nil {
+					// Nothing in this node's set offers it either, so there is genuinely nothing
+					// to say. Resolution has already refused anything unanswerable, so this is a
+					// requirement met by the module itself.
+					continue
+				}
+				found = here
 			}
 			file, err := boundFile(*found, m.Binds[to])
 			if err != nil {
@@ -429,3 +441,28 @@ func (r Resolution) ContributionsTo(requirement string, settings SettingsBy) (
 	}
 	return given[0].From, given[0].Values, nil
 }
+
+// here is the module on this same machine that answers a requirement, as a binding.
+//
+// **Only when the provider said something a consumer must know.** That is the line: the original
+// reasoning — a file saying "it is on this node" is a fact nobody needs — is right about the
+// location and wrong about everything beside it. A shell is answered here and there is nothing to
+// say about it. A registry is answered here and the consumer still cannot guess the port.
+//
+// The address is this machine's own name on the private network when it has one, and loopback
+// when it does not — a machine not on the network still reaches itself, and naming it by a name
+// nothing resolves would be worse than naming it by an address that always works.
+func here(r Resolution, requirement string) *Needed {
+	for _, m := range r.Modules {
+		serves, said := m.Serves[requirement]
+		if !said || len(serves) == 0 {
+			continue
+		}
+		at := r.At
+		if at == "" {
+			at = "127.0.0.1"
+		}
+		return &Needed{Name: requirement, From: r.Node, At: at, Serves: serves}
+	}
+	return nil
+}

internal/catalogue/filtering_test.go

@@ -299,3 +299,68 @@ func (computedOnce) Resources(string) ([]map[string]any, bool, error) {
 	return []map[string]any{{"id": "wg", "type": "file", "path": "/etc/wireguard/wg0.conf",
 		"content": "x", "mode": "0600"}}, true, nil
 }
+
+// A consumer bound to something answered on its own machine still has to be told where it is.
+//
+// The location is a fact nobody needs — "it is here" — and everything beside it is not: the
+// binding carries what the provider said a consumer must know, which is the port. A build machine
+// sharing a node with the registry it pushes to sat in a loop saying it could not read its own
+// binding, because none was written.
+func TestSomethingAnsweredOnThisMachineIsStillBound(t *testing.T) {
+	r := Resolution{
+		Node: "anchor", At: "anchor.internal",
+		Modules: []Manifest{
+			{Module: "registry", Provides: []Offer{{Name: "artifact-store", Scope: ScopeMesh}},
+				Serves: map[string]map[string]any{"artifact-store": {"port": 5000}}},
+			{Module: "builder", Requires: []string{"artifact-store"},
+				Binds: map[string]string{"artifact-store": "/var/lib/builder/store.json"}},
+		},
+	}
+	out, err := r.Declaration(Rendering{})
+	if err != nil {
+		t.Fatalf("declaration: %v", err)
+	}
+	var content string
+	for _, res := range out {
+		if res["path"] == "/var/lib/builder/store.json" {
+			content, _ = res["content"].(string)
+		}
+	}
+	if content == "" {
+		t.Fatal("nothing was written, so the consumer cannot find a provider on its own machine")
+	}
+	if !strings.Contains(content, "5000") {
+		t.Fatalf("the binding does not carry the port, which is the part nobody can guess:\n%s", content)
+	}
+	if !strings.Contains(content, "anchor.internal") {
+		t.Fatalf("the binding does not say where to reach it:\n%s", content)
+	}
+}
+
+// And a machine not on the private network still reaches itself.
+func TestAMachineOffTheNetworkIsBoundToItselfByAnAddressThatWorks(t *testing.T) {
+	r := Resolution{
+		Node: "alone",
+		Modules: []Manifest{
+			{Module: "registry", Provides: []Offer{{Name: "artifact-store", Scope: ScopeMesh}},
+				Serves: map[string]map[string]any{"artifact-store": {"port": 5000}}},
+			{Module: "builder", Requires: []string{"artifact-store"},
+				Binds: map[string]string{"artifact-store": "/var/lib/builder/store.json"}},
+		},
+	}
+	out, err := r.Declaration(Rendering{})
+	if err != nil {
+		t.Fatalf("declaration: %v", err)
+	}
+	for _, res := range out {
+		if res["path"] != "/var/lib/builder/store.json" {
+			continue
+		}
+		content, _ := res["content"].(string)
+		if !strings.Contains(content, "127.0.0.1") {
+			t.Fatalf("bound by a name nothing on this machine resolves:\n%s", content)
+		}
+		return
+	}
+	t.Fatal("nothing was written")
+}

internal/catalogue/resolve.go

@@ -74,6 +74,10 @@ type Held struct {
 type Resolution struct {
 	// Node is which machine this was resolved for, so a generator can be asked about it.
 	Node string
+	// At is this machine's own name on the private network, empty if it is not on one. Kept
+	// because a consumer bound to something answered on this same machine still has to be told
+	// where it is — the answer being local does not make the port guessable.
+	At string
 
 	// Modules in the order they were resolved: assigned first, then what they pulled in.
 	Modules []Manifest
@@ -320,7 +324,7 @@ func Resolve(catalogue map[string]Manifest, assigned []string, node Node, world
 		}
 	}
 
-	resolution := Resolution{Node: node.Name, Because: because, Needs: needs}
+	resolution := Resolution{Node: node.Name, At: node.At, Because: because, Needs: needs}
 	for _, n := range order {
 		resolution.Modules = append(resolution.Modules, catalogue[n])
 	}