diff --git a/contracts/go/seats/meshartifactsweep/contract.go b/contracts/go/seats/meshartifactsweep/contract.go
new file mode 100644
index 00000000..8aa87d21
--- /dev/null
+++ b/contracts/go/seats/meshartifactsweep/contract.go
@@ -0,0 +1,129 @@
+// Code generated by seatgen from the seat definitions; DO NOT EDIT.
+
+// Package meshartifactsweep is the contract of the seat "mesh-artifact-sweep", defined whole (seats/mesh-artifact-sweep/seat.json): no description.
+package meshartifactsweep
+
+import "time"
+
+// Seat is the seat's name.
+const Seat = "mesh-artifact-sweep"
+
+const (
+	VerbArtifacts = "artifacts"
+	VerbHeld      = "held"
+	VerbCollect   = "collect"
+	VerbMirrors   = "mirrors"
+	VerbImages    = "images"
+)
+
+const (
+	EventArtifactsGone = "artifacts-gone"
+)
+
+// Verbs is every verb the seat serves, in its definition's order: a new copy each call.
+func Verbs() []string {
+	return []string{VerbArtifacts, VerbHeld, VerbCollect, VerbMirrors, VerbImages}
+}
+
+// Events is every event published on the seat's subject: a new copy each call.
+func Events() []string {
+	return []string{EventArtifactsGone}
+}
+
+// Family is where the seat's events are kept: the shared events stream, filtered to the seat's subjects.
+const (
+	Family           = "mesh-artifact-sweep.events"
+	FamilyMaxAgeDays = 7
+)
+
+// SubjectArtifactsGone is where artifacts-gone is published.
+const SubjectArtifactsGone = "mesh.seat.mesh-artifact-sweep.event.artifacts-gone"
+
+// ArtifactsGone is the body of artifacts-gone.
+type ArtifactsGone struct {
+	// when the sweep found it
+	At *time.Time `json:"at,omitempty"`
+	// artifacts-gone
+	Event string `json:"event"`
+	// the key's fingerprint
+	Fingerprint string `json:"fingerprint"`
+	// every reference of the key the store does not hold, sorted
+	Gone []string `json:"gone"`
+	// the builder's done key
+	Key string `json:"key,omitempty"`
+	// the module whose builder's key names a gone artifact
+	Module string `json:"module"`
+}
+
+// ArtifactsInput is what artifacts takes.
+type ArtifactsInput struct {
+	// "true": list the collected references too (counted always)
+	Collected string `json:"collected,omitempty"`
+	// only this repository's references, as <module>/<artifact> (the counts stay whole)
+	Repository string `json:"repository,omitempty"`
+}
+
+// The values of ArtifactsInput's collected.
+const (
+	ArtifactsInputCollectedTrue  = "true"
+	ArtifactsInputCollectedFalse = "false"
+)
+
+// ArtifactsAnswer is what artifacts answers.
+type ArtifactsAnswer = map[string]any
+
+// HeldInput is what held takes.
+type HeldInput struct {
+	// the artifacts' references, artifact-store://<module>/<artifact>/blobs/sha256:<hex>: a list, or one text separated by commas
+	References []string `json:"references"`
+}
+
+// HeldAnswer is what held answers.
+type HeldAnswer struct {
+	// the references the store answered 404 for
+	Gone []string `json:"gone"`
+	// the references the store holds
+	Held []string `json:"held"`
+	// the store asked, host and port
+	Store string `json:"store,omitempty"`
+	// a reference the store could not be asked about, to why
+	Unknown map[string]string `json:"unknown,omitempty"`
+}
+
+// CollectInput is what collect takes.
+type CollectInput struct {
+	// "true": let go of what is eligible (needs why); without it nothing is done
+	Confirm string `json:"confirm,omitempty"`
+	// let go of at most this many (500 by default, at most 5000)
+	Most string `json:"most,omitempty"`
+	// with confirm: why, required and recorded
+	Why string `json:"why,omitempty"`
+}
+
+// The values of CollectInput's confirm.
+const (
+	CollectInputConfirmTrue  = "true"
+	CollectInputConfirmFalse = "false"
+)
+
+// CollectAnswer is what collect answers.
+type CollectAnswer = map[string]any
+
+// MirrorsInput is what mirrors takes.
+type MirrorsInput struct {
+}
+
+// MirrorsAnswer is what mirrors answers.
+type MirrorsAnswer = map[string]any
+
+// ImagesInput is what images takes.
+type ImagesInput struct {
+	// the machine's name
+	Node string `json:"node"`
+}
+
+// ImagesAnswer is what images answers.
+type ImagesAnswer = map[string]any
+
+// ArtifactsGoneEvent is the body of the event artifacts-gone.
+type ArtifactsGoneEvent = ArtifactsGone
diff --git a/contracts/go/seats/meshartifactsweep/contract_test.go b/contracts/go/seats/meshartifactsweep/contract_test.go
new file mode 100644
index 00000000..ea7a5f1f
--- /dev/null
+++ b/contracts/go/seats/meshartifactsweep/contract_test.go
@@ -0,0 +1,54 @@
+// Code generated by seatgen from the seat definitions; DO NOT EDIT.
+
+package meshartifactsweep
+
+import (
+	"encoding/json"
+	"reflect"
+	"regexp"
+	"testing"
+)
+
+// TestFixtures reads every fixture of seats/mesh-artifact-sweep/fixtures: each decodes into its type, a field the type does not
+// know is dropped (ADR 0608 §6), and it reads back as its wire says; each subject named is the contract's.
+func TestFixtures(t *testing.T) {
+	cases := []struct {
+		name, subject, given, wire string
+		decode                     func([]byte) (any, error)
+		subjectIs                  *regexp.Regexp
+	}{
+		{name: "artifacts-gone on the seat's subject", subject: "mesh.seat.mesh-artifact-sweep.event.artifacts-gone", given: "{\"at\":\"2026-11-05T15:04:05Z\",\"event\":\"artifacts-gone\",\"fingerprint\":\"f1\",\"gone\":[\"artifact-store://ca-trust/archive/blobs/sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\",\"artifact-store://ca-trust/archive/blobs/sha256:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\"],\"key\":\"ca-trust.archive.f1\",\"module\":\"ca-trust\"}", wire: "{\"at\":\"2026-11-05T15:04:05Z\",\"event\":\"artifacts-gone\",\"fingerprint\":\"f1\",\"gone\":[\"artifact-store://ca-trust/archive/blobs/sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\",\"artifact-store://ca-trust/archive/blobs/sha256:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\"],\"key\":\"ca-trust.archive.f1\",\"module\":\"ca-trust\"}",
+			decode: func(b []byte) (any, error) { var v ArtifactsGoneEvent; err := json.Unmarshal(b, &v); return v, err }, subjectIs: regexp.MustCompile("^mesh\\.seat\\.mesh-artifact-sweep\\.event\\.artifacts-gone$")},
+		{name: "held asks the references", subject: "", given: "{\"references\":[\"artifact-store://ca-trust/archive/blobs/sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\",\"artifact-store://ca-trust/archive/blobs/sha256:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\",\"artifact-store://ca-trust/archive/blobs/sha256:cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc\"]}", wire: "{\"references\":[\"artifact-store://ca-trust/archive/blobs/sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\",\"artifact-store://ca-trust/archive/blobs/sha256:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\",\"artifact-store://ca-trust/archive/blobs/sha256:cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc\"]}",
+			decode: func(b []byte) (any, error) { var v HeldInput; err := json.Unmarshal(b, &v); return v, err }, subjectIs: nil},
+		{name: "held answers held, gone and unknown", subject: "", given: "{\"gone\":[\"artifact-store://ca-trust/archive/blobs/sha256:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\"],\"held\":[\"artifact-store://ca-trust/archive/blobs/sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\"],\"store\":\"store.test:5100\",\"unknown\":{\"artifact-store://ca-trust/archive/blobs/sha256:cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc\":\"the store answered 503\"}}", wire: "{\"gone\":[\"artifact-store://ca-trust/archive/blobs/sha256:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\"],\"held\":[\"artifact-store://ca-trust/archive/blobs/sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\"],\"store\":\"store.test:5100\",\"unknown\":{\"artifact-store://ca-trust/archive/blobs/sha256:cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc\":\"the store answered 503\"}}",
+			decode: func(b []byte) (any, error) { var v HeldAnswer; err := json.Unmarshal(b, &v); return v, err }, subjectIs: nil},
+		{name: "held answers with nothing unknown", subject: "", given: "{\"gone\":[],\"held\":[],\"store\":\"store.test:5100\"}", wire: "{\"gone\":[],\"held\":[],\"store\":\"store.test:5100\"}",
+			decode: func(b []byte) (any, error) { var v HeldAnswer; err := json.Unmarshal(b, &v); return v, err }, subjectIs: nil},
+	}
+	for _, c := range cases {
+		v, err := c.decode([]byte(c.given))
+		if err != nil {
+			t.Errorf("%s: does not decode: %v", c.name, err)
+			continue
+		}
+		back, err := json.Marshal(v)
+		if err != nil {
+			t.Errorf("%s: does not encode: %v", c.name, err)
+			continue
+		}
+		var got, want any
+		if err := json.Unmarshal(back, &got); err != nil {
+			t.Fatal(err)
+		}
+		if err := json.Unmarshal([]byte(c.wire), &want); err != nil {
+			t.Fatal(err)
+		}
+		if !reflect.DeepEqual(got, want) {
+			t.Errorf("%s: reads back as %s, want %s", c.name, back, c.wire)
+		}
+		if c.subjectIs != nil && !c.subjectIs.MatchString(c.subject) {
+			t.Errorf("%s: subject %q is not the contract's %s", c.name, c.subject, c.subjectIs)
+		}
+	}
+}
diff --git a/contracts/go/seats/meshartifactsweep/go.mod b/contracts/go/seats/meshartifactsweep/go.mod
new file mode 100644
index 00000000..77f0649b
--- /dev/null
+++ b/contracts/go/seats/meshartifactsweep/go.mod
@@ -0,0 +1,3 @@
+module git.novox.be/novox/mesh-delivery/contracts/go/seats/meshartifactsweep
+
+go 1.26.0
diff --git a/contracts/module.json b/contracts/module.json
index d80c383c..09be597e 100644
--- a/contracts/module.json
+++ b/contracts/module.json
@@ -23,6 +23,16 @@
         "series": "0.1",
         "generated-from": "."
       },
+      {
+        "name": "go-meshartifactsweep",
+        "kind": "package",
+        "language": "go",
+        "paths": [
+          "go/seats/meshartifactsweep"
+        ],
+        "series": "0.1",
+        "generated-from": "."
+      },
       {
         "name": "go-meshcatalog",
         "kind": "package",
@@ -186,6 +196,16 @@
         "series": "0.1",
         "generated-from": "."
       },
+      {
+        "name": "ts-meshartifactsweep",
+        "kind": "package",
+        "language": "typescript",
+        "paths": [
+          "ts/seats/meshartifactsweep"
+        ],
+        "series": "0.1",
+        "generated-from": "."
+      },
       {
         "name": "ts-meshcatalog",
         "kind": "package",
diff --git a/contracts/seats/mesh-artifact-sweep/fixtures/events.json b/contracts/seats/mesh-artifact-sweep/fixtures/events.json
new file mode 100644
index 00000000..3e39336a
--- /dev/null
+++ b/contracts/seats/mesh-artifact-sweep/fixtures/events.json
@@ -0,0 +1,15 @@
+[
+  {
+    "name": "artifacts-gone on the seat's subject",
+    "of": "event:artifacts-gone",
+    "subject": "mesh.seat.mesh-artifact-sweep.event.artifacts-gone",
+    "given": {
+      "event": "artifacts-gone",
+      "module": "ca-trust",
+      "key": "ca-trust.archive.f1",
+      "fingerprint": "f1",
+      "gone": ["artifact-store://ca-trust/archive/blobs/sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", "artifact-store://ca-trust/archive/blobs/sha256:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"],
+      "at": "2026-11-05T15:04:05Z"
+    }
+  }
+]
diff --git a/contracts/seats/mesh-artifact-sweep/fixtures/states.json b/contracts/seats/mesh-artifact-sweep/fixtures/states.json
new file mode 100644
index 00000000..fe51488c
--- /dev/null
+++ b/contracts/seats/mesh-artifact-sweep/fixtures/states.json
@@ -0,0 +1 @@
+[]
diff --git a/contracts/seats/mesh-artifact-sweep/fixtures/verbs.json b/contracts/seats/mesh-artifact-sweep/fixtures/verbs.json
new file mode 100644
index 00000000..b70970ee
--- /dev/null
+++ b/contracts/seats/mesh-artifact-sweep/fixtures/verbs.json
@@ -0,0 +1,24 @@
+[
+  {
+    "name": "held asks the references",
+    "of": "verb:held.input",
+    "why": "the references are the holder's own test values (the tool refuses a call without them through the console)",
+    "given": {"references": ["artifact-store://ca-trust/archive/blobs/sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", "artifact-store://ca-trust/archive/blobs/sha256:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb", "artifact-store://ca-trust/archive/blobs/sha256:cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc"]}
+  },
+  {
+    "name": "held answers held, gone and unknown",
+    "of": "verb:held.answer",
+    "why": "the answer of the holder's test (cmd/artifact-store-tools): every reference in one of the three",
+    "given": {
+      "store": "store.test:5100",
+      "held": ["artifact-store://ca-trust/archive/blobs/sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"],
+      "gone": ["artifact-store://ca-trust/archive/blobs/sha256:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"],
+      "unknown": {"artifact-store://ca-trust/archive/blobs/sha256:cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc": "the store answered 503"}
+    }
+  },
+  {
+    "name": "held answers with nothing unknown",
+    "of": "verb:held.answer",
+    "given": {"store": "store.test:5100", "held": [], "gone": []}
+  }
+]
diff --git a/contracts/seats/mesh-artifact-sweep/seat.json b/contracts/seats/mesh-artifact-sweep/seat.json
index 2e5b673d..4763ce8d 100644
--- a/contracts/seats/mesh-artifact-sweep/seat.json
+++ b/contracts/seats/mesh-artifact-sweep/seat.json
@@ -2,7 +2,7 @@
   "format": 1,
   "seat": "mesh-artifact-sweep",
   "scope": "mesh",
-  "grain": "seat-list",
+  "grain": "whole",
   "domain": "Delivery",
   "decision": "novox/hq ADR 0571",
   "verbs": [
@@ -25,6 +25,10 @@
           }
         },
         "type": "object"
+      },
+      "answer": {
+        "type": "object",
+        "description": "what artifacts answers, as its description says"
       }
     },
     {
@@ -44,6 +48,41 @@
           "references"
         ],
         "type": "object"
+      },
+      "answer": {
+        "type": "object",
+        "properties": {
+          "store": {
+            "type": "string",
+            "description": "the store asked, host and port"
+          },
+          "held": {
+            "type": "array",
+            "items": {
+              "type": "string"
+            },
+            "description": "the references the store holds"
+          },
+          "gone": {
+            "type": "array",
+            "items": {
+              "type": "string"
+            },
+            "description": "the references the store answered 404 for"
+          },
+          "unknown": {
+            "type": "object",
+            "additionalProperties": {
+              "type": "string"
+            },
+            "description": "a reference the store could not be asked about, to why"
+          }
+        },
+        "required": [
+          "held",
+          "gone"
+        ],
+        "description": "what held answers: a reference is in held, gone or unknown, never none of them"
       }
     },
     {
@@ -69,6 +108,10 @@
           }
         },
         "type": "object"
+      },
+      "answer": {
+        "type": "object",
+        "description": "what collect answers, as its description says"
       }
     },
     {
@@ -77,6 +120,10 @@
       "input": {
         "properties": {},
         "type": "object"
+      },
+      "answer": {
+        "type": "object",
+        "description": "what mirrors answers, as its description says"
       }
     },
     {
@@ -93,12 +140,65 @@
           "node"
         ],
         "type": "object"
+      },
+      "answer": {
+        "type": "object",
+        "description": "what images answers, as its description says"
       }
     }
   ],
+  "family": {
+    "name": "mesh-artifact-sweep.events",
+    "max-age-days": 7
+  },
   "events": [
     {
-      "name": "artifacts-gone"
+      "name": "artifacts-gone",
+      "body": {
+        "$ref": "#/defs/ArtifactsGone"
+      }
     }
-  ]
+  ],
+  "defs": {
+    "ArtifactsGone": {
+      "type": "object",
+      "properties": {
+        "event": {
+          "type": "string",
+          "description": "artifacts-gone"
+        },
+        "module": {
+          "type": "string",
+          "description": "the module whose builder's key names a gone artifact"
+        },
+        "key": {
+          "type": "string",
+          "description": "the builder's done key"
+        },
+        "fingerprint": {
+          "type": "string",
+          "description": "the key's fingerprint"
+        },
+        "gone": {
+          "type": "array",
+          "items": {
+            "type": "string"
+          },
+          "description": "every reference of the key the store does not hold, sorted"
+        },
+        "at": {
+          "type": "string",
+          "format": "date-time",
+          "description": "when the sweep found it"
+        }
+      },
+      "required": [
+        "event",
+        "module",
+        "fingerprint",
+        "gone"
+      ],
+      "description": "the body of artifacts-gone"
+    }
+  }
 }
diff --git a/contracts/ts/seats/meshartifactsweep/package-lock.json b/contracts/ts/seats/meshartifactsweep/package-lock.json
new file mode 100644
index 00000000..2d3064d4
--- /dev/null
+++ b/contracts/ts/seats/meshartifactsweep/package-lock.json
@@ -0,0 +1,12 @@
+{
+  "lockfileVersion": 3,
+  "name": "@novox/mesh-delivery-contracts-mesh-artifact-sweep",
+  "packages": {
+    "": {
+      "name": "@novox/mesh-delivery-contracts-mesh-artifact-sweep",
+      "version": "0.1.0"
+    }
+  },
+  "requires": true,
+  "version": "0.1.0"
+}
diff --git a/contracts/ts/seats/meshartifactsweep/package.json b/contracts/ts/seats/meshartifactsweep/package.json
new file mode 100644
index 00000000..14c46319
--- /dev/null
+++ b/contracts/ts/seats/meshartifactsweep/package.json
@@ -0,0 +1,13 @@
+{
+  "description": "The contract of the seat mesh-artifact-sweep, generated from its definition.",
+  "exports": {
+    ".": "./src/index.ts"
+  },
+  "files": [
+    "src"
+  ],
+  "name": "@novox/mesh-delivery-contracts-mesh-artifact-sweep",
+  "type": "module",
+  "types": "./src/index.ts",
+  "version": "0.1.0"
+}
diff --git a/contracts/ts/seats/meshartifactsweep/src/index.ts b/contracts/ts/seats/meshartifactsweep/src/index.ts
new file mode 100644
index 00000000..ad4d48a4
--- /dev/null
+++ b/contracts/ts/seats/meshartifactsweep/src/index.ts
@@ -0,0 +1,99 @@
+// Code generated by seatgen from the seat definitions; DO NOT EDIT.
+
+// The contract of the seat "mesh-artifact-sweep", defined whole (seats/mesh-artifact-sweep/seat.json): no description.
+
+export const seat = "mesh-artifact-sweep";
+
+export const verbs = {
+  artifacts: "artifacts",
+  held: "held",
+  collect: "collect",
+  mirrors: "mirrors",
+  images: "images",
+} as const;
+
+export const events = {
+  artifactsGone: "artifacts-gone",
+} as const;
+
+export const family = { name: "mesh-artifact-sweep.events", maxAgeDays: 7 } as const;
+
+export const artifactsGoneSubject = "mesh.seat.mesh-artifact-sweep.event.artifacts-gone";
+
+/** the body of artifacts-gone */
+export interface ArtifactsGone {
+  /** when the sweep found it */
+  "at"?: string;
+  /** artifacts-gone */
+  "event": string;
+  /** the key's fingerprint */
+  "fingerprint": string;
+  /** every reference of the key the store does not hold, sorted */
+  "gone": string[];
+  /** the builder's done key */
+  "key"?: string;
+  /** the module whose builder's key names a gone artifact */
+  "module": string;
+}
+
+/** is what artifacts takes. */
+export interface ArtifactsInput {
+  /** "true": list the collected references too (counted always) */
+  "collected"?: "true" | "false";
+  /** only this repository's references, as <module>/<artifact> (the counts stay whole) */
+  "repository"?: string;
+}
+
+/** is what artifacts answers. */
+export type ArtifactsAnswer = Record<string, unknown>;
+
+/** is what held takes. */
+export interface HeldInput {
+  /** the artifacts' references, artifact-store://<module>/<artifact>/blobs/sha256:<hex>: a list, or one text separated by commas */
+  "references": string[];
+}
+
+/** is what held answers. */
+export interface HeldAnswer {
+  /** the references the store answered 404 for */
+  "gone": string[];
+  /** the references the store holds */
+  "held": string[];
+  /** the store asked, host and port */
+  "store"?: string;
+  /** a reference the store could not be asked about, to why */
+  "unknown"?: Record<string, string>;
+}
+
+/** is what collect takes. */
+export interface CollectInput {
+  /** "true": let go of what is eligible (needs why); without it nothing is done */
+  "confirm"?: "true" | "false";
+  /** let go of at most this many (500 by default, at most 5000) */
+  "most"?: string;
+  /** with confirm: why, required and recorded */
+  "why"?: string;
+}
+
+/** is what collect answers. */
+export type CollectAnswer = Record<string, unknown>;
+
+/** is what mirrors takes. */
+export interface MirrorsInput {
+}
+
+/** is what mirrors answers. */
+export type MirrorsAnswer = Record<string, unknown>;
+
+/** is what images takes. */
+export interface ImagesInput {
+  /** the machine's name */
+  "node": string;
+}
+
+/** is what images answers. */
+export type ImagesAnswer = Record<string, unknown>;
+
+/** is the body of the event artifacts-gone. */
+export type ArtifactsGoneEvent = ArtifactsGone;
+
diff --git a/contracts/ts/seats/meshartifactsweep/tsconfig.json b/contracts/ts/seats/meshartifactsweep/tsconfig.json
new file mode 100644
index 00000000..60274c6a
--- /dev/null
+++ b/contracts/ts/seats/meshartifactsweep/tsconfig.json
@@ -0,0 +1,12 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "noEmit": true,
+    "strict": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true
+  },
+  "include": ["src/**/*.ts"]
+}
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/gone_integration_test.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/gone_integration_test.go
index bf59a418..ee342ee6 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/gone_integration_test.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/gone_integration_test.go
@@ -12,6 +12,7 @@ import (
 	"github.com/nats-io/nats.go"
 	"github.com/nats-io/nats.go/jetstream"
 
+	sweep "git.novox.be/novox/mesh-delivery/contracts/go/seats/meshartifactsweep"
 	"git.novox.be/novox/mesh-sdk/go/catalogue"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
 )
@@ -35,7 +36,7 @@ func (h *heldVerb) serve(t *testing.T, b *bed) {
 			References []string `json:"references"`
 		}
 		_ = json.Unmarshal(m.Data, &args)
-		a := delivery.HeldAnswer{Store: "store.test:5100", Held: []string{}, Gone: []string{}}
+		a := sweep.HeldAnswer{Store: "store.test:5100", Held: []string{}, Gone: []string{}}
 		h.mu.Lock()
 		for _, r := range args.References {
 			h.asked = append(h.asked, r)
@@ -69,7 +70,7 @@ func eventsConsumer(t *testing.T, b *bed, node string) {
 		t.Fatal(err)
 	}
 	if _, err := b.js.CreateOrUpdateConsumer(b.ctx, eventsStream, jetstream.ConsumerConfig{Durable: node + "_mesh-delivery-builder",
-		AckPolicy: jetstream.AckExplicitPolicy, FilterSubjects: []string{delivery.ArtifactsGoneSubject}}); err != nil {
+		AckPolicy: jetstream.AckExplicitPolicy, FilterSubjects: []string{sweep.SubjectArtifactsGone}}); err != nil {
 		t.Fatal(err)
 	}
 }
@@ -168,12 +169,13 @@ func TestArtifactsGoneLeadsTheBuilderToBuildTheKeyAgain(t *testing.T) {
 	collected = true
 	mu.Unlock()
 	key, _ := delivery.BuilderBuildKey("ca-trust", fp)
-	body, err := delivery.EncodeArtifactsGone(delivery.ArtifactsGone{Module: "ca-trust", Key: key, Fingerprint: fp,
-		Gone: []string{ref}, At: time.Now().UTC()})
+	at := time.Now().UTC()
+	body, err := json.Marshal(sweep.ArtifactsGone{Event: sweep.EventArtifactsGone, Module: "ca-trust", Key: key, Fingerprint: fp,
+		Gone: []string{ref}, At: &at})
 	if err != nil {
 		t.Fatal(err)
 	}
-	if _, err := b.js.Publish(b.ctx, delivery.ArtifactsGoneSubject, body); err != nil {
+	if _, err := b.js.Publish(b.ctx, sweep.SubjectArtifactsGone, body); err != nil {
 		t.Fatal(err)
 	}
 	v := b.await(t, "ca-trust", func(v delivery.BuilderBuild) bool {
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/integration_test.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/integration_test.go
index 795fd0c0..882a56a8 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/integration_test.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/integration_test.go
@@ -28,6 +28,7 @@ import (
 	runner "git.novox.be/novox/mesh-catalog/modules/mesh-build-go/buildstep"
 	"git.novox.be/novox/mesh-contracts/go/seats/gopackageregistry"
 	"git.novox.be/novox/mesh-contracts/go/seats/ociartifactregistry"
+	sweep "git.novox.be/novox/mesh-delivery/contracts/go/seats/meshartifactsweep"
 	"git.novox.be/novox/mesh-sdk/go/buildstep"
 	"git.novox.be/novox/mesh-sdk/go/buscompose"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/main.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/main.go
index 927a8ad9..5559b78b 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/main.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/main.go
@@ -26,6 +26,7 @@ import (
 	"github.com/nats-io/nats.go"
 	"github.com/nats-io/nats.go/jetstream"
 
+	sweep "git.novox.be/novox/mesh-delivery/contracts/go/seats/meshartifactsweep"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
 	"git.novox.be/novox/mesh-sdk/go/process"
 	"git.novox.be/novox/mesh-sdk/go/views"
@@ -352,7 +353,7 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 	reader.Start(ctx, js, cred, process.AwaitBucket(ctx, js, conn, firstViewsBucket, "builder_first_views reads nothing and builder_first_view_again is not heard", logger.Printf))
 	// Every part has registered: the hub pulls the module's durable. Where the consumer is not there yet the builder says so
 	// and binds it at a later change (heard.Writer; ADR 0615 §5).
-	_ = notHeard.Bind(eventsStream, delivery.ArtifactsGoneEvent+", what wakes a floor, the registry seats' words, the views and manifest-reads-changed are not heard until the builder starts again", func() error {
+	_ = notHeard.Bind(eventsStream, sweep.EventArtifactsGone+", what wakes a floor, the registry seats' words, the views and manifest-reads-changed are not heard until the builder starts again", func() error {
 		return hub.Start(ctx, js, cred)
 	})
 	go func() { <-ctx.Done(); hub.Stop() }()
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/refused_test.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/refused_test.go
index 0e53e2f2..cc000338 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/refused_test.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/refused_test.go
@@ -21,6 +21,7 @@ import (
 	"github.com/nats-io/nats.go/jetstream"
 
 	"git.novox.be/novox/mesh-contracts/go/seats/nodeengine"
+	sweep "git.novox.be/novox/mesh-delivery/contracts/go/seats/meshartifactsweep"
 	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-builder/buildrun"
 	"git.novox.be/novox/mesh-delivery/sdk/enginereads"
 	"git.novox.be/novox/mesh-delivery/sdk/forms"
@@ -223,7 +224,7 @@ func aFloorsWakeIsHeard(t *testing.T) {
 	if !f.heard(context.Background(), cleared) || !strings.Contains(logs.String(), "the floor of m/img is asked again: condition-cleared") {
 		t.Fatalf("condition-cleared: log %q", logs.String())
 	}
-	if f.heard(context.Background(), &wakeMsg{subject: delivery.ArtifactsGoneSubject}) {
+	if f.heard(context.Background(), &wakeMsg{subject: sweep.SubjectArtifactsGone}) {
 		t.Fatal("artifacts-gone was taken as a floor's wake")
 	}
 	// DLV-B4: a registry seat's outcome on the same consumer moves a version; a published wakes a name whose seat was
diff --git a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/stored.go b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/stored.go
index c5fc876a..7c1a023e 100644
--- a/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/stored.go
+++ b/modules/mesh-delivery-builder/cmd/mesh-delivery-builder/stored.go
@@ -9,8 +9,8 @@ import (
 
 	"github.com/nats-io/nats.go/jetstream"
 
+	sweep "git.novox.be/novox/mesh-delivery/contracts/go/seats/meshartifactsweep"
 	"git.novox.be/novox/mesh-sdk/go/catalogue"
-	"git.novox.be/novox/mesh-sdk/go/delivery"
 
 	"mesh-delivery-builder/internal/build"
 )
@@ -35,7 +35,7 @@ func storedVia(call toolCaller) func(ctx context.Context, references []string) (
 		if err != nil {
 			return nil, fmt.Errorf("asking held: %w", err)
 		}
-		a, err := delivery.DecodeHeldAnswer(raw, references)
+		a, err := decodeHeld(raw, references)
 		if err != nil {
 			return nil, err
 		}
@@ -54,13 +54,62 @@ func storedVia(call toolCaller) func(ctx context.Context, references []string) (
 // heardGone takes one artifacts-gone event in: acknowledged, then handed to the builder, which asks the store and builds
 // the key again. A body that is not one is said and acknowledged, so it is not handed over again.
 func heardGone(ctx context.Context, b *build.Builder, m jetstream.Msg, logf func(string, ...any)) {
-	e, err := delivery.DecodeArtifactsGone(m.Data())
+	e, err := decodeGone(m.Data())
 	if ackErr := m.Ack(); ackErr != nil {
 		logf("acknowledging %s: %v", m.Subject(), ackErr)
 	}
 	if err != nil {
-		logf("%s holds what is not %s, left: %v", m.Subject(), delivery.ArtifactsGoneEvent, err)
+		logf("%s holds what is not %s, left: %v", m.Subject(), sweep.EventArtifactsGone, err)
 		return
 	}
 	b.ArtifactsGone(ctx, e)
 }
+
+// decodeHeld reads the seat's answer to held: the verb answers {output, ok, answer}, the answer being the seat's
+// HeldAnswer. A reference asked that the answer names in none of held, gone and unknown is an error: an answer that
+// leaves one out would let a key with a gone blob be reused.
+func decodeHeld(raw []byte, asked []string) (sweep.HeldAnswer, error) {
+	var wrapped struct {
+		Output string          `json:"output"`
+		OK     bool            `json:"ok"`
+		Answer json.RawMessage `json:"answer"`
+	}
+	if err := json.Unmarshal(raw, &wrapped); err != nil {
+		return sweep.HeldAnswer{}, fmt.Errorf("the answer of %s is not {output, ok, answer}: %w", SeatHeld, err)
+	}
+	if !wrapped.OK || len(wrapped.Answer) == 0 {
+		return sweep.HeldAnswer{}, fmt.Errorf("%s did not answer: %s", SeatHeld, wrapped.Output)
+	}
+	var a sweep.HeldAnswer
+	if err := json.Unmarshal(wrapped.Answer, &a); err != nil {
+		return sweep.HeldAnswer{}, fmt.Errorf("the answer of %s is not {held, gone}: %w", SeatHeld, err)
+	}
+	named := map[string]bool{}
+	for _, r := range a.Held {
+		named[r] = true
+	}
+	for _, r := range a.Gone {
+		named[r] = true
+	}
+	for r := range a.Unknown {
+		named[r] = true
+	}
+	for _, r := range asked {
+		if !named[r] {
+			return sweep.HeldAnswer{}, fmt.Errorf("the answer of %s names nothing of %s", SeatHeld, r)
+		}
+	}
+	return a, nil
+}
+
+// decodeGone reads the event's body, refusing one that names no module, fingerprint or reference.
+func decodeGone(raw []byte) (sweep.ArtifactsGone, error) {
+	var e sweep.ArtifactsGone
+	if err := json.Unmarshal(raw, &e); err != nil {
+		return sweep.ArtifactsGone{}, fmt.Errorf("%s is not one: %w", sweep.EventArtifactsGone, err)
+	}
+	if e.Event != sweep.EventArtifactsGone || e.Module == "" || e.Fingerprint == "" || len(e.Gone) == 0 {
+		return sweep.ArtifactsGone{}, fmt.Errorf("%s names no module, fingerprint or gone reference: %s", sweep.EventArtifactsGone, raw)
+	}
+	return e, nil
+}
diff --git a/modules/mesh-delivery-builder/go.mod b/modules/mesh-delivery-builder/go.mod
index a493ed16..cfa50977 100644
--- a/modules/mesh-delivery-builder/go.mod
+++ b/modules/mesh-delivery-builder/go.mod
@@ -47,3 +47,7 @@ require (
 )
 
 replace git.novox.be/novox/mesh-delivery/sdk => ../../sdk
+
+require git.novox.be/novox/mesh-delivery/contracts/go/seats/meshartifactsweep v0.0.0-00010101000000-000000000000
+
+replace git.novox.be/novox/mesh-delivery/contracts/go/seats/meshartifactsweep => ../../contracts/go/seats/meshartifactsweep
diff --git a/modules/mesh-delivery-builder/internal/build/gone_test.go b/modules/mesh-delivery-builder/internal/build/gone_test.go
index 499cdbc9..c114010a 100644
--- a/modules/mesh-delivery-builder/internal/build/gone_test.go
+++ b/modules/mesh-delivery-builder/internal/build/gone_test.go
@@ -9,6 +9,7 @@ import (
 	"sync"
 	"testing"
 
+	sweep "git.novox.be/novox/mesh-delivery/contracts/go/seats/meshartifactsweep"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
 )
 
@@ -184,14 +185,14 @@ func TestArtifactsGoneMakesTheBuilderAskAndBuildAgain(t *testing.T) {
 	held.mu.Lock()
 	held.gone[goneRef] = true // collected after the builder's look; the controller's take-in found it
 	held.mu.Unlock()
-	r.b.ArtifactsGone(context.Background(), delivery.ArtifactsGone{Event: delivery.ArtifactsGoneEvent, Module: "m",
+	r.b.ArtifactsGone(context.Background(), sweep.ArtifactsGone{Event: sweep.EventArtifactsGone, Module: "m",
 		Fingerprint: "src2:" + strings.Repeat("9", 64), Gone: []string{goneRef}})
 	r.b.Wait()
 	if r.st.revs[r.key] != rev || !log.has("a fingerprint the module does not have now") {
 		t.Fatalf("an event for another fingerprint moved the key (revision %d, was %d): %v", r.st.revs[r.key], rev, log.lines)
 	}
 
-	r.b.ArtifactsGone(context.Background(), delivery.ArtifactsGone{Event: delivery.ArtifactsGoneEvent, Module: "m",
+	r.b.ArtifactsGone(context.Background(), sweep.ArtifactsGone{Event: sweep.EventArtifactsGone, Module: "m",
 		Key: r.key, Fingerprint: fp1, Gone: []string{goneRef}})
 	r.b.Wait()
 	v := valueOf(t, r.st, r.key)
diff --git a/modules/mesh-delivery-builder/internal/build/run.go b/modules/mesh-delivery-builder/internal/build/run.go
index fecf91c8..e651e436 100644
--- a/modules/mesh-delivery-builder/internal/build/run.go
+++ b/modules/mesh-delivery-builder/internal/build/run.go
@@ -13,6 +13,7 @@ import (
 	"sync"
 	"time"
 
+	sweep "git.novox.be/novox/mesh-delivery/contracts/go/seats/meshartifactsweep"
 	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-builder/buildrun"
 	"git.novox.be/novox/mesh-delivery/sdk/forms"
 	"git.novox.be/novox/mesh-sdk/go/buildstep"
@@ -281,7 +282,7 @@ func (b *Builder) storedOnce(key string) func(ctx context.Context, references []
 // that the store does not hold what the module's key names. The module is looked at again, which asks the store (ClaimOptions.Stored) and
 // builds the key again; an event for a fingerprint the module no longer has is said and left. The event only wakes the
 // builder: what is built rests on the store's answer, never on the event alone.
-func (b *Builder) ArtifactsGone(ctx context.Context, e delivery.ArtifactsGone) {
+func (b *Builder) ArtifactsGone(ctx context.Context, e sweep.ArtifactsGone) {
 	b.init()
 	b.mu.Lock()
 	m, ok := b.known[e.Module]
@@ -295,11 +296,11 @@ func (b *Builder) ArtifactsGone(ctx context.Context, e delivery.ArtifactsGone) {
 	b.mu.Unlock()
 	if !ok || m.FP2 != e.Fingerprint {
 		b.logf("%s: heard %s for %s, a fingerprint the module does not have now: nothing to build", e.Module,
-			delivery.ArtifactsGoneEvent, e.Fingerprint)
+			sweep.EventArtifactsGone, e.Fingerprint)
 		return
 	}
 	b.logf("%s: heard %s (%s): asking the artifact store and building the key again", e.Module,
-		delivery.ArtifactsGoneEvent, strings.Join(e.Gone, ", "))
+		sweep.EventArtifactsGone, strings.Join(e.Gone, ", "))
 	b.consider(ctx, e.Module, m)
 }