diff --git a/cmd/mesh-controller/sendable_test.go b/cmd/mesh-controller/sendable_test.go
index 749599f..f831e34 100644
--- a/cmd/mesh-controller/sendable_test.go
+++ b/cmd/mesh-controller/sendable_test.go
@@ -330,11 +330,15 @@ func TestTheMachineSideOfAMappingIsMovedEverywhereTheNumberIsUsed(t *testing.T)
 	if opening == nil || opening["to"] != 22 || opening["from"] != catalogue.OpeningFromMesh {
 		t.Fatalf("no opening for the port this node gave the forge: %v", opening)
 	}
+	var guard map[string]any
 	for _, r := range resources {
-		if r["id"] == catalogue.GuardID() && r["content"] != catalogue.AsGuard([]int{222}) {
-			t.Fatalf("the guard does not refuse the port the forge is on:\n%s", r["content"])
+		if r["id"] == catalogue.GuardID() {
+			guard = r
 		}
 	}
+	if guard == nil || guard["content"] != catalogue.AsGuard([]int{222}) {
+		t.Fatalf("the guard does not refuse the port the forge is on:\n%v", guard["content"])
+	}
 
 	// And the consumer on the other machine dials the same number.
 	plan, _, err := planFor(ctx, open, "laptop")
diff --git a/internal/catalogue/adoption_test.go b/internal/catalogue/adoption_test.go
index bf4c405..7f313d6 100644
--- a/internal/catalogue/adoption_test.go
+++ b/internal/catalogue/adoption_test.go
@@ -3,6 +3,7 @@ package catalogue
 import (
 	"encoding/json"
 	"reflect"
+	"slices"
 	"strings"
 	"testing"
 )
@@ -448,6 +449,12 @@ func aForge() Manifest {
 // here because everything below — the filter, the openings, the guard, what a consumer is told —
 // reads that map, and a given port that the lookup does not find moves the container's mapping
 // and nothing else.
+//
+// It stands in for the plan only where the plan does not allocate: a port the manifest already
+// placed, or one a node was given. For a short form with no given port the real plan asks the
+// inventory for a machine port and may come back with one from the pool, which needs a store and
+// is what cmd/mesh-controller's own tests exercise. So an assertion here about such a port asserts
+// this helper, not the mesh; keep the assertions to the ports under test.
 func portsAsThePlanWould(m Manifest, given map[int]int) map[int]int {
 	out := map[int]int{}
 	for _, l := range m.Listens {
@@ -470,19 +477,21 @@ func TestAGivenPortNamesEitherEndOfWhatTheModulePublishes(t *testing.T) {
 	}
 
 	// The machine side — the number this module says it listens on, and the one the predecessor
-	// had somewhere else. Answered under both ends, because the plan looks a given port up by the
-	// port the module declares and the container's mapping is rewritten by the port inside it.
+	// had somewhere else. Answered under 2222, the end the module itself names, which is what
+	// every reader of this map asks for. One entry, not two: a second key for the same answer is
+	// an entry another mapping's reader could find instead.
 	given, err := GivenPorts(forge, node(map[string]any{"2222": float64(222)}))
 	if err != nil {
 		t.Fatalf("the machine side of a mapping cannot be given a port: %v", err)
 	}
-	if given[2222] != 222 || given[22] != 222 {
-		t.Fatalf("the forge was given %v, and its mapping has two ends", given)
+	if want := map[int]int{2222: 222}; !reflect.DeepEqual(given, want) {
+		t.Fatalf("the forge was given %v; the mapping it names is filed under %v", given, want)
 	}
 
-	// The container's own port names the same mapping and means the same thing.
+	// The container's own port names the same mapping and means the same thing — and is filed
+	// under the same name, because the module's name for it has not changed.
 	if inside, err := GivenPorts(forge, node(map[string]any{"22": float64(222)})); err != nil ||
-		inside[2222] != 222 || inside[22] != 222 {
+		!reflect.DeepEqual(inside, map[int]int{2222: 222}) {
 		t.Fatalf("the container's end of the mapping was given %v: %v", inside, err)
 	}
 
@@ -520,6 +529,38 @@ func TestAGivenPortNamesEitherEndOfWhatTheModulePublishes(t *testing.T) {
 		!strings.Contains(err.Error(), "twice") {
 		t.Fatalf("a number naming two of the module's mappings was accepted: %v", err)
 	}
+
+	// And the same refusal when the number naming two mappings is not the one the setting used
+	// but the one the answer would be filed under. Here `80` is the module's own name for a
+	// mapping, and two mappings wear it; filing an answer there is one container's port standing
+	// where the other's is read, and both containers then publish it.
+	shared := Manifest{Module: "gallery",
+		Listens: []Listening{{Port: 80, From: FromMesh}},
+		Resources: []map[string]any{
+			{"id": "a", "type": "container", "name": "a", "ports": []any{"4001:80"}},
+			{"id": "b", "type": "container", "name": "b", "ports": []any{"4002:80"}}}}
+	if _, err := GivenPorts(shared, node(map[string]any{"4001": float64(1234)})); err == nil ||
+		!strings.Contains(err.Error(), "twice") {
+		t.Fatalf("two containers were put on one machine port: %v", err)
+	}
+
+	// A module whose mappings chain — one's machine side is another's container port — keeps them
+	// apart, because each is filed under the port the module names it by and neither name is
+	// shared. Given both, each moves on its own and neither overwrites the other.
+	chained := Manifest{Module: "chain",
+		Listens: []Listening{{Port: 80, From: FromMesh}, {Port: 9090, From: FromMesh}},
+		Resources: []map[string]any{{"id": "server", "type": "container", "name": "chain",
+			"ports": []any{"8080:80", "9090:8080"}}}}
+	both, err := GivenPorts(chained, node(map[string]any{"80": float64(1234), "9090": float64(5678)}))
+	if err != nil || !reflect.DeepEqual(both, map[int]int{80: 1234, 9090: 5678}) {
+		t.Fatalf("chained mappings were given %v: %v", both, err)
+	}
+	if moved := givenOuter("8080:80", both); moved != "1234:80" {
+		t.Fatalf("the first mapping moved to %q, and it was given 1234", moved)
+	}
+	if moved := givenOuter("9090:8080", both); moved != "5678:8080" {
+		t.Fatalf("the second mapping moved to %q, and it was given 5678", moved)
+	}
 }
 
 // And the number reaches everything derived from it. The fault this is written against moved the
@@ -560,7 +601,10 @@ func TestAGivenMachineSideReachesTheFilterTheOpeningAndTheConsumer(t *testing.T)
 	for _, rule := range rules {
 		opened = append(opened, rule.Port)
 	}
-	if !reflect.DeepEqual(opened, []int{222, 3000}) {
+	// Only the moved port is asserted: the forge's other port is a short form the real plan would
+	// allocate rather than read off the manifest, so its number here is portsAsThePlanWould's and
+	// not the mesh's.
+	if !slices.Contains(opened, 222) || slices.Contains(opened, 2222) {
 		t.Fatalf("the filter opens %v, not where the machine puts the forge", opened)
 	}
 
@@ -577,7 +621,8 @@ func TestAGivenMachineSideReachesTheFilterTheOpeningAndTheConsumer(t *testing.T)
 	}
 
 	// The guard refuses it where the machine put it, and nothing where it used to be.
-	if guard, _ := got[GuardID()]["content"].(string); guard != AsGuard([]int{222, 3000}) {
+	guard, _ := got[GuardID()]["content"].(string)
+	if !strings.Contains(guard, "222") || strings.Contains(guard, "2222") {
 		t.Fatalf("the guard does not follow the given port:\n%s", guard)
 	}
 
diff --git a/internal/catalogue/filtering.go b/internal/catalogue/filtering.go
index 994c2b0..fd3c78f 100644
--- a/internal/catalogue/filtering.go
+++ b/internal/catalogue/filtering.go
@@ -2,6 +2,7 @@ package catalogue
 
 import (
 	"fmt"
+	"slices"
 	"sort"
 	"strconv"
 	"strings"
@@ -484,14 +485,19 @@ const MeshWideLayer = "the mesh"
 // what consumers are told while the software still listens on the old one — a port that reads as
 // moved and is not.
 //
-// **Either name of a mapping names it.** A short form publishes one number, which is the
-// container's port and the machine's at once. A mapping written the long way — `"2222:22"` — has
-// two, and a module reasonably declares it listens on either: the port its software uses, or the
-// port the machine already serves on. Both are accepted, and both come back, so that whoever
-// reads this — the ports map, the filter, the openings, what a consumer is told, and the mapping
-// the runtime is handed — finds the same number under the key it happens to hold. Keyed one way
-// and read the other, the setting moved the container's mapping and nothing else: a firewall,
-// a set of openings and a consumer all pointing at a port the software had left.
+// **Either name of a mapping names it; the module's own name answers.** A short form publishes one
+// number, which is the container's port and the machine's at once. A mapping written the long way
+// — `"2222:22"` — has two, and a module reasonably declares it listens on either: the port its
+// software uses, or the port the machine already serves on. A setting may name either end, because
+// both are true of the same mapping. The answer comes back under the end the **module** names in
+// its `listens`, which is the number every reader of this map holds: the ports map, the filter, the
+// openings, what a consumer is told, and the mapping the runtime is handed. Keyed one way and read
+// the other, the setting moved the container's mapping and nothing else — a firewall, a set of
+// openings and a consumer all pointing at a port the software had left.
+//
+// One entry per mapping, never two. A second key for the same answer is not a convenience: where
+// two mappings share a number, it is an entry one of them writes over the other's, and the reader
+// that finds the survivor disagrees with the reader that recomputes it.
 func GivenPorts(m Manifest, layers []Layer) (map[int]int, error) {
 	// Every name a setting may use, and the mapping it names.
 	names := map[int][]publishing{}
@@ -501,8 +507,16 @@ func GivenPorts(m Manifest, layers []Layer) (map[int]int, error) {
 			names[p.machine] = append(names[p.machine], p)
 		}
 	}
-	chose := map[int]int{}        // the port a setting named → the machine port it gave it
-	meant := map[int]publishing{} // and which of the module's mappings that was
+	// And the names the module itself uses. A mapping's answer is filed under these, because they
+	// are what every reader asks for; a mapping the module names at neither end is filed under its
+	// machine side, where nothing looks, which is correct — nothing serves it.
+	declares := map[int]bool{}
+	for _, l := range m.Listens {
+		declares[l.Port] = true
+	}
+	chose := map[int]int{} // the port a setting named → the machine port it gave it
+	out := map[int]int{}   // the port the module names → the machine port it is on
+	by := map[int]int{}    // and which of the setting's ports put it there, for the refusal
 	for _, layer := range layers {
 		raw, ok := layer.Values[PortsSetting]
 		if !ok {
@@ -528,15 +542,8 @@ func GivenPorts(m Manifest, layers []Layer) (map[int]int, error) {
 					"publishes %d — the mesh cannot move a port the module does not publish; the "+
 					"software would go on listening where it was told to", m.Module, port, port)
 			}
-			// The same number naming two different mappings — `"22"` beside `"2222:22"`, say.
-			// Refused rather than picked: moving one of them and leaving the other is a mapping
-			// the operator did not ask for and cannot see, and the two readings differ.
-			for _, other := range publishes[1:] {
-				if other != publishes[0] {
-					return nil, fmt.Errorf("%s gives port %d a machine port, and its containers "+
-						"publish %d twice — as %s and as %s; which one to move is not said",
-						m.Module, port, port, publishes[0], other)
-				}
+			if err := oneMapping(m.Module, port, publishes); err != nil {
+				return nil, err
 			}
 			at, ok := asPort(value)
 			if !ok || at < 1 || at > 65535 {
@@ -548,13 +555,11 @@ func GivenPorts(m Manifest, layers []Layer) (map[int]int, error) {
 					"one port a machine may never lose", m.Module, port, at)
 			}
 			chose[port] = at
-			meant[port] = publishes[0]
 		}
 	}
-	// One holder per machine port, within the module too — which also settles a mapping named at
-	// both ends, because the machine publishes it once whichever end the setting called it.
+	// One holder per machine port, within the module too.
 	holder := map[int]int{}
-	for _, port := range sorted(chose) {
+	for _, port := range sortedPorts(chose) {
 		at := chose[port]
 		if other, twice := holder[at]; twice {
 			return nil, fmt.Errorf("%s gives machine port %d to both its %d and its %d", m.Module,
@@ -562,21 +567,35 @@ func GivenPorts(m Manifest, layers []Layer) (map[int]int, error) {
 		}
 		holder[at] = port
 	}
-	// And one machine port per mapping: `{"22": 222, "2222": 300}` is two numbers for the one
-	// thing the machine publishes, and neither is more right.
-	out := map[int]int{}
-	said := map[publishing]int{}
-	for _, port := range sorted(chose) {
-		at, mapped := chose[port], meant[port]
-		if was, twice := said[mapped]; twice {
-			return nil, fmt.Errorf("%s gives %s the machine ports %d and %d — its %d and its %d "+
-				"are the two ends of one mapping, and it is published once", m.Module, mapped,
-				min(was, at), max(was, at), min(mapped.machine, mapped.inner),
-				max(mapped.machine, mapped.inner))
+	// Filed under the module's own names for the mapping — every one it uses, so a module that
+	// says it listens on both ends is answered at both, and under the machine side when it names
+	// neither.
+	for _, port := range sortedPorts(chose) {
+		at, mapping := chose[port], names[port][0]
+		keys := []int{}
+		for _, end := range []int{mapping.machine, mapping.inner} {
+			if declares[end] && !slices.Contains(keys, end) {
+				keys = append(keys, end)
+			}
+		}
+		if len(keys) == 0 {
+			keys = []int{mapping.machine}
+		}
+		for _, key := range keys {
+			// The key must name this mapping and no other, or the entry is one mapping's answer
+			// standing where another's is read.
+			if err := oneMapping(m.Module, key, names[key]); err != nil {
+				return nil, err
+			}
+			// And one machine port per mapping: `{"22": 222, "2222": 300}` is two numbers for the
+			// one thing the machine publishes, and neither is more right.
+			if was, twice := out[key]; twice && was != at {
+				return nil, fmt.Errorf("%s gives %s the machine ports %d and %d — its %d and its "+
+					"%d are the two ends of one mapping, and it is published once", m.Module,
+					mapping, min(was, at), max(was, at), min(by[key], port), max(by[key], port))
+			}
+			out[key], by[key] = at, port
 		}
-		said[mapped] = at
-		out[mapped.inner] = at
-		out[mapped.machine] = at
 	}
 	if len(out) == 0 {
 		return nil, nil
@@ -584,6 +603,21 @@ func GivenPorts(m Manifest, layers []Layer) (map[int]int, error) {
 	return out, nil
 }
 
+// oneMapping refuses a number that names two of a module's mappings — `"22"` beside `"2222:22"`,
+// say, or `"4001:80"` beside `"4002:80"` read by their shared `80`. Refused rather than picked:
+// moving one of them and leaving the other is a mapping the operator did not ask for and cannot
+// see, and the two readings differ.
+func oneMapping(module string, port int, publishes []publishing) error {
+	for _, other := range publishes[1:] {
+		if other != publishes[0] {
+			return fmt.Errorf("%s gives port %d a machine port, and its containers publish %d "+
+				"twice — as %s and as %s; which one to move is not said", module, port, port,
+				publishes[0], other)
+		}
+	}
+	return nil
+}
+
 // publishing is one mapping a module's container writes: the port the container itself uses, and
 // the machine port the manifest put it on — the same number for a short form, which the runtime
 // publishes on the port it names.
@@ -621,8 +655,8 @@ func publishedPorts(m Manifest) []publishing {
 	return out
 }
 
-// sorted is a settings map's ports in order, so a refusal reads the same on every run.
-func sorted(of map[int]int) []int {
+// sortedPorts is a settings map's ports in order, so a refusal reads the same on every run.
+func sortedPorts(of map[int]int) []int {
 	out := make([]int, 0, len(of))
 	for port := range of {
 		out = append(out, port)
diff --git a/internal/catalogue/foundation_manifests_test.go b/internal/catalogue/foundation_manifests_test.go
index ff4ce36..5f032c6 100644
--- a/internal/catalogue/foundation_manifests_test.go
+++ b/internal/catalogue/foundation_manifests_test.go
@@ -266,10 +266,10 @@ func TestTheForgesSshPortIsGivenByTheNumberTheForgeCallsIt(t *testing.T) {
 	if err != nil {
 		t.Fatalf("the forge's ssh port cannot be given on a node: %v", err)
 	}
-	// Under the number the module listens on, which is how the plan finds it, and under the
-	// container's own port, which is how the mapping is rewritten.
-	if given[2222] != 222 || given[22] != 222 {
-		t.Fatalf("the forge was given %v", given)
+	// Under the number the module listens on — 2222, the machine side of its mapping — which is
+	// the number the plan, the filter, the openings and the consumer all ask for. One entry.
+	if want := map[int]int{2222: 222}; !reflect.DeepEqual(given, want) {
+		t.Fatalf("the forge was given %v, and it names its ssh port %v", given, want)
 	}
 
 	resolved, err := forge.Resolve([]Built{{