diff --git a/COORDINATOR_RUNBOOK.md b/COORDINATOR_RUNBOOK.md
index 525c2c9..274108f 100644
--- a/COORDINATOR_RUNBOOK.md
+++ b/COORDINATOR_RUNBOOK.md
@@ -161,6 +161,13 @@ head. It downloads into a fresh review directory and invokes
 the new head. Inbox submissions remain available for review or provider
 lifecycle cleanup.
 
+By default Relay records `accepted_at` from the coordinator clock after the
+candidate download, preserving subsecond precision so it is strictly later
+than the participant's signed `destroyed_at`. Keep participant and coordinator
+clocks synchronized. Use `--accepted-at RFC3339` only for a controlled replay;
+the explicit value must still be strictly later than the signed erasure and
+the preceding accepted record.
+
 Repeat for every participant and phase.
 
 ## 5. Publish lifecycle changes
diff --git a/cmd/relay/coordinator_workflow.go b/cmd/relay/coordinator_workflow.go
index 9706ef6..56cb5af 100644
--- a/cmd/relay/coordinator_workflow.go
+++ b/cmd/relay/coordinator_workflow.go
@@ -71,7 +71,7 @@ func runAcceptCandidate(args []string) error {
 	set.StringVar(&root, "root", "", "coordinator transcript root")
 	set.StringVar(&candidateDir, "candidate-dir", "", "fresh local directory for the downloaded candidate")
 	set.StringVar(&coordinatorSigningKey, "coordinator-signing-key", "", "coordinator Ed25519 private key")
-	set.StringVar(&acceptedAt, "accepted-at", "", "acceptance timestamp (defaults to now)")
+	set.StringVar(&acceptedAt, "accepted-at", "", "acceptance timestamp (defaults to the current time after candidate download)")
 	set.StringVar(&phase1Seal, "phase1-seal", "", "phase 2: sealed phase-1 record")
 	set.StringVar(&phase1SealSignature, "phase1-seal-signature", "", "phase 2: phase-1 seal signature")
 	set.BoolVar(&verify, "verify-publish", false, "confirm every published object after advancing the head")
@@ -81,11 +81,10 @@ func runAcceptCandidate(args []string) error {
 	if storagePath == "" || candidateKey == "" || root == "" || candidateDir == "" || coordinatorSigningKey == "" {
 		return errors.New("--storage, --candidate-key, --root, --candidate-dir and --coordinator-signing-key are required")
 	}
-	if acceptedAt == "" {
-		acceptedAt = time.Now().UTC().Format(time.RFC3339)
-	}
-	if _, err := time.Parse(time.RFC3339, acceptedAt); err != nil {
-		return errors.New("--accepted-at must be RFC3339")
+	if acceptedAt != "" {
+		if _, err := time.Parse(time.RFC3339, acceptedAt); err != nil {
+			return errors.New("--accepted-at must be RFC3339")
+		}
 	}
 	if !safeObjectKey(candidateKey) || !strings.HasSuffix(candidateKey, "/manifest.json") {
 		return errors.New("--candidate-key must be a safe manifest object key")
@@ -161,6 +160,9 @@ func runAcceptCandidate(args []string) error {
 	}); err != nil {
 		return err
 	}
+	if acceptedAt == "" {
+		acceptedAt = defaultAcceptanceTimestamp(time.Now())
+	}
 	command := []string{manifest.Phase, "verify", "--ceremony", config.CeremonyPath,
 		"--ceremony-signature", config.CeremonySignature, "--coordinator-public-key-file", config.CoordinatorPublicKey,
 		"--transcript-dir", root, "--chain", pos.chainPath, "--chain-signature", pos.chain.ChainSignaturePath,
@@ -198,6 +200,10 @@ func runAcceptCandidate(args []string) error {
 	return nil
 }
 
+func defaultAcceptanceTimestamp(now time.Time) string {
+	return now.UTC().Format(time.RFC3339Nano)
+}
+
 func runEvidenceInbox(args []string) error {
 	set := flag.NewFlagSet("coordinator evidence", flag.ContinueOnError)
 	var storagePath, role string
diff --git a/cmd/relay/coordinator_workflow_test.go b/cmd/relay/coordinator_workflow_test.go
new file mode 100644
index 0000000..d39b37a
--- /dev/null
+++ b/cmd/relay/coordinator_workflow_test.go
@@ -0,0 +1,23 @@
+package main
+
+import (
+	"testing"
+	"time"
+)
+
+func TestDefaultAcceptanceTimestampPreservesSubsecondOrdering(t *testing.T) {
+	destroyedAt := time.Date(2026, time.August, 20, 12, 0, 0, 0, time.UTC)
+	acceptedAt := destroyedAt.Add(time.Nanosecond)
+
+	encoded := defaultAcceptanceTimestamp(acceptedAt)
+	decoded, err := time.Parse(time.RFC3339Nano, encoded)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !decoded.After(destroyedAt) {
+		t.Fatalf("accepted_at %q is not strictly after destroyed_at %q", encoded, destroyedAt.Format(time.RFC3339Nano))
+	}
+	if !decoded.Equal(acceptedAt) {
+		t.Fatalf("accepted_at = %q, want %q", encoded, acceptedAt.Format(time.RFC3339Nano))
+	}
+}
diff --git a/cmd/relay/proof_tool_integration_test.go b/cmd/relay/proof_tool_integration_test.go
index 91c24e1..0ded352 100644
--- a/cmd/relay/proof_tool_integration_test.go
+++ b/cmd/relay/proof_tool_integration_test.go
@@ -20,6 +20,7 @@ import (
 //
 // Run the fast compatibility checks with:
 //
+//	(cd /path/to/proof-tool && bash scripts/bootstrap-vendor.sh)
 //	RELAY_PROOF_TOOL_DIR=/path/to/proof-tool go test ./cmd/relay \
 //	  -run TestProofToolCompatibility -v
 //
@@ -274,7 +275,8 @@ func testProofToolContributionCommands(t *testing.T, ceremonyBinary, fixtureRoot
 		"--coordinator-public-key-file", inspector.CoordinatorPublicKeyPath,
 		"--transcript-dir", ceremonyRoot, "--chain", chainPath,
 		"--chain-signature", chainSignature, "--candidate-dir", candidateDir,
-		"--coordinator-signing-key", coordinatorSigningKey, "--accepted-at", "2026-08-18T12:02:00Z")
+		"--coordinator-signing-key", coordinatorSigningKey,
+		"--accepted-at", defaultAcceptanceTimestamp(time.Now().Add(time.Second)))
 	accepted, err := inspector.Chain(
 		filepath.Join(ceremonyRoot, "phase1", "chain-0001.json"),
 		filepath.Join(ceremonyRoot, "phase1", "chain-0001.sig"),
@@ -300,7 +302,7 @@ func writeTestJSON(t *testing.T, path string, value any) {
 
 func buildProofProgram(t *testing.T, proofToolDir, output, packagePath string) {
 	t.Helper()
-	command := exec.Command("go", "build", "-mod=mod", "-o", output, packagePath)
+	command := exec.Command("go", "build", "-mod=vendor", "-o", output, packagePath)
 	command.Dir = proofToolDir
 	if combined, err := command.CombinedOutput(); err != nil {
 		t.Fatalf("build proof-tool program %s: %v\n%s", packagePath, err, combined)
diff --git a/docs/RELEASE.md b/docs/RELEASE.md
index d71ecfa..1e20d70 100644
--- a/docs/RELEASE.md
+++ b/docs/RELEASE.md
@@ -209,12 +209,25 @@ exact clean checkout can build the CLI directly:
       checkout --detach "$PROOF_TOOL_COMMIT"
     (
       cd "$RELEASE_EVIDENCE_ROOT/proof-tool-source"
-      CGO_ENABLED=0 go build -trimpath -buildvcs=true \
+      bash scripts/bootstrap-vendor.sh
+      CGO_ENABLED=0 go build -mod=vendor -trimpath -buildvcs=true \
         -o "$RELEASE_EVIDENCE_ROOT/mpc-ceremony" ./cmd/mpc-ceremony
     )
 
 Never use `go run` for `mpc-ceremony`; the program requires VCS metadata that
-`go run` omits.
+`go run` omits. Do not replace the vendored build above with `-mod=mod`:
+proof-tool's reviewed gnark changes are applied by `bootstrap-vendor.sh` and
+must be present in the tested binary.
+
+Before approving a coordinated release, exercise Relay against that exact
+proof-tool checkout, including the production-sized contribution and
+acceptance path:
+
+    cd /path/to/relay
+    RELAY_PROOF_TOOL_DIR="$RELEASE_EVIDENCE_ROOT/proof-tool-source" \
+    RELAY_PROOF_TOOL_FULL=1 \
+      go test ./cmd/relay -run '^TestProofToolCompatibility$' -count=1 \
+        -timeout 30m -v
 
 For a production proof-tool release, follow its repository's approved signed
 tag and reproducible-release procedure using