diff --git a/lib/scaffold.sh b/lib/scaffold.sh
index fbefb6c..5add2ed 100644
--- a/lib/scaffold.sh
+++ b/lib/scaffold.sh
@@ -4,6 +4,9 @@
 # Directory structure creation and template rendering engine.
 # =============================================================================
 
+# Canonical directory layout lives in one place (lib/structure.sh).
+source "$(dirname "${BASH_SOURCE[0]}")/structure.sh"
+
 render_template() {
   local template_file="$1"
   local output_file="$2"
@@ -32,13 +35,9 @@ render_template() {
 
 scaffold_genome() {
   local base="$1"
-  local dirs=(
-    "raw/articles" "raw/transcripts" "raw/code-packs" "raw/assets" "raw/private"
-    "wiki/sources" "wiki/entities" "wiki/concepts" "wiki/queries" "wiki/private"
-  )
 
   info "Building directory structure in ${base}..."
-  for dir in "${dirs[@]}"; do
+  for dir in "${GENOME_DIRS[@]}"; do
     mkdir -p "${base}/${dir}"
     touch "${base}/${dir}/.gitkeep"
   done
diff --git a/lib/structure.sh b/lib/structure.sh
new file mode 100644
index 0000000..f94bba1
--- /dev/null
+++ b/lib/structure.sh
@@ -0,0 +1,70 @@
+#!/usr/bin/env bash
+# =============================================================================
+# lib/structure.sh
+# Single source of truth for the canonical genome directory layout, plus the
+# verify/sync helpers used by scripts/verify-genomes.sh.
+#
+# IMPORTANT: this is the ONE place the structure is defined. scaffold.sh sources
+# this file and builds new genomes from GENOME_DIRS, so scaffolding and the
+# structure check can never drift apart.
+# =============================================================================
+
+# Canonical directories every genome must have.
+# raw/* are input buckets (collaborator-writable); wiki/* is the agent-owned,
+# contract-bound layout the lint, the index sections and the ingest skill depend on.
+GENOME_DIRS=(
+  "raw/articles" "raw/transcripts" "raw/code-packs" "raw/assets" "raw/private"
+  "wiki/sources" "wiki/entities" "wiki/concepts" "wiki/queries" "wiki/private"
+)
+
+# ---------------------------------------------------------------------------
+# structure_report <base>
+# Reports drift of <base> against GENOME_DIRS.
+#   - missing canonical dir            → counted as drift (returns non-zero)
+#   - extra dir under raw/ or wiki/    → warning only (does not fail)
+# Returns the number of MISSING canonical directories.
+# ---------------------------------------------------------------------------
+structure_report() {
+  local base="$1"
+  local missing=0
+
+  for d in "${GENOME_DIRS[@]}"; do
+    if [[ ! -d "${base}/${d}" ]]; then
+      warn "missing: ${d}"
+      missing=$((missing + 1))
+    fi
+  done
+
+  # Extra directories (drift the other way) — informational only.
+  local canon=" ${GENOME_DIRS[*]} "
+  while IFS= read -r d; do
+    d="${d#"${base}/"}"
+    [[ "$canon" == *" ${d} "* ]] && continue
+    info "extra (not in canon): ${d}"
+  done < <(find "${base}/raw" "${base}/wiki" -mindepth 1 -type d 2>/dev/null)
+
+  return $missing
+}
+
+# ---------------------------------------------------------------------------
+# structure_sync <base>
+# Creates any MISSING canonical directories (idempotent). Never deletes —
+# retiring a bucket is a deliberate, contract-aware change to GENOME_DIRS +
+# the templates, not an automatic prune.
+# ---------------------------------------------------------------------------
+structure_sync() {
+  local base="$1"
+  local added=0
+
+  for d in "${GENOME_DIRS[@]}"; do
+    if [[ ! -d "${base}/${d}" ]]; then
+      mkdir -p "${base}/${d}"
+      touch "${base}/${d}/.gitkeep"
+      success "created: ${d}"
+      added=$((added + 1))
+    fi
+  done
+
+  [[ $added -eq 0 ]] && info "already in sync: ${base}"
+  return 0
+}
diff --git a/scripts/verify-genomes.sh b/scripts/verify-genomes.sh
new file mode 100644
index 0000000..85a4a62
--- /dev/null
+++ b/scripts/verify-genomes.sh
@@ -0,0 +1,50 @@
+#!/usr/bin/env bash
+# =============================================================================
+# scripts/verify-genomes.sh
+# Check (default) or --sync the directory structure of every registered genome
+# against the canonical layout in lib/structure.sh.
+#
+#   bash scripts/verify-genomes.sh           # report drift, non-zero exit on drift
+#   bash scripts/verify-genomes.sh --sync    # create missing dirs everywhere (safe)
+#
+# No hardware/LLM involved — pure structure check. Run anywhere.
+# =============================================================================
+set -euo pipefail
+source "lib/output.sh"
+source "globals.env"
+source "registry.sh"
+source "lib/structure.sh"
+
+MODE="verify"
+[[ "${1:-}" == "--sync" ]] && MODE="sync"
+
+step "Genome structure: ${MODE}"
+
+TOTAL_MISSING=0
+for entry in "${GENOMES[@]}"; do
+  IFS='|' read -r GENOME_NAME _ _ <<< "$entry"     # 3-field registry; ignore desc + linked
+  genome_dir="${WORK_DIR}/${MASTER_REPO}/${GENOME_NAME}"
+
+  if [[ ! -d "$genome_dir" ]]; then
+    warn "not found locally, skipping: ${GENOME_NAME}"
+    continue
+  fi
+
+  info "Genome: ${GENOME_NAME}"
+  if [[ "$MODE" == "sync" ]]; then
+    structure_sync "$genome_dir"
+  else
+    structure_report "$genome_dir" && m=0 || m=$?
+    TOTAL_MISSING=$((TOTAL_MISSING + m))
+  fi
+done
+
+echo ""
+if [[ "$MODE" == "sync" ]]; then
+  success "Structure sync complete."
+elif [[ $TOTAL_MISSING -eq 0 ]]; then
+  success "Structure verified: all genomes match the canonical layout."
+else
+  error "Structure drift: ${TOTAL_MISSING} missing directory(ies). Fix with: make sync-structure"
+  exit 1
+fi