diff --git a/scripts/migrate-workdir-layout-20260724.sh b/scripts/migrate-workdir-layout-20260724.sh
new file mode 100755
index 00000000..ad0ddfca
--- /dev/null
+++ b/scripts/migrate-workdir-layout-20260724.sh
@@ -0,0 +1,164 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+usage() {
+  cat <<'USAGE'
+Usage:
+  scripts/migrate-workdir-layout-20260724.sh --workdir-target <PATH> [--apply]
+
+Migrates old runtime workdir materialization layout:
+
+  <workdir-target>/working-directories/<id>/materialization.json
+  <workdir-target>/working-directories/<id>/root/<repository-id>/
+
+to the new layout:
+
+  <workdir-target>/<id>/materialization.json
+  <workdir-target>/<id>/checkout/
+
+The script defaults to dry-run. It mutates files only when --apply is passed.
+Run this while the runtime/server and workers using the target are stopped.
+
+Options:
+  --workdir-target <PATH>  Runtime workdir materialization target.
+  --apply                 Perform migration. Without this, only prints actions.
+  -h, --help              Show this help.
+
+Requirements:
+  bash, git, jq, mktemp
+USAGE
+}
+
+log() {
+  printf '%s\n' "$*"
+}
+
+fail() {
+  printf 'error: %s\n' "$*" >&2
+  exit 1
+}
+
+need_cmd() {
+  command -v "$1" >/dev/null 2>&1 || fail "required command not found: $1"
+}
+
+json_string() {
+  local file=$1
+  local expr=$2
+  jq -er "$expr | strings" "$file"
+}
+
+apply=0
+workdir_target=""
+
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    --workdir-target)
+      [[ $# -ge 2 ]] || fail "--workdir-target requires a path"
+      workdir_target=$2
+      shift 2
+      ;;
+    --apply)
+      apply=1
+      shift
+      ;;
+    -h|--help)
+      usage
+      exit 0
+      ;;
+    *)
+      fail "unknown argument: $1"
+      ;;
+  esac
+done
+
+[[ -n "$workdir_target" ]] || fail "--workdir-target is required"
+need_cmd git
+need_cmd jq
+need_cmd mktemp
+
+[[ -d "$workdir_target" ]] || fail "workdir target does not exist or is not a directory: $workdir_target"
+old_root=$workdir_target/working-directories
+if [[ ! -d "$old_root" ]]; then
+  log "no old workdir layout found: $old_root"
+  exit 0
+fi
+
+if [[ $apply -eq 0 ]]; then
+  log "dry-run: no files will be changed; pass --apply to migrate"
+else
+  log "apply: migrating old workdir layout under $workdir_target"
+fi
+
+shopt -s nullglob
+records=("$old_root"/*/materialization.json)
+shopt -u nullglob
+
+if [[ ${#records[@]} -eq 0 ]]; then
+  log "no materialization records found under $old_root"
+  exit 0
+fi
+
+migrated=0
+
+for record in "${records[@]}"; do
+  old_dir=$(dirname "$record")
+  workdir_id=$(basename "$old_dir")
+  new_dir=$workdir_target/$workdir_id
+  new_record=$new_dir/materialization.json
+  new_checkout=$new_dir/checkout
+
+  old_checkout=$(json_string "$record" '.root')
+  source_repository_path=$(json_string "$record" '.source_repository_path')
+
+  [[ "$old_checkout" = "$old_dir"/root/* ]] || fail "$record root is not under expected old root/<repository-id> layout: $old_checkout"
+  [[ -d "$old_checkout" ]] || fail "$record root does not exist or is not a directory: $old_checkout"
+  [[ -d "$source_repository_path" ]] || fail "$record source_repository_path does not exist or is not a directory: $source_repository_path"
+
+  root_parent=$(dirname "$old_checkout")
+  [[ "$root_parent" = "$old_dir/root" ]] || fail "$record root parent is not $old_dir/root: $root_parent"
+
+  shopt -s nullglob dotglob
+  root_children=("$old_dir/root"/*)
+  shopt -u nullglob dotglob
+  [[ ${#root_children[@]} -eq 1 ]] || fail "$old_dir/root must contain exactly one checkout; found ${#root_children[@]}"
+  [[ "${root_children[0]}" = "$old_checkout" ]] || fail "$record root does not match the only checkout under $old_dir/root"
+
+  if [[ -e "$new_dir" && "$new_dir" != "$old_dir" ]]; then
+    fail "target workdir directory already exists: $new_dir"
+  fi
+  if [[ -e "$new_checkout" ]]; then
+    fail "target checkout already exists: $new_checkout"
+  fi
+  if [[ -e "$new_record" ]]; then
+    fail "target materialization record already exists: $new_record"
+  fi
+
+  log "workdir $workdir_id"
+  log "  move checkout: $old_checkout -> $new_checkout"
+  log "  rewrite record: $record -> $new_record"
+  log "  repair git worktree metadata in: $source_repository_path"
+
+  if [[ $apply -eq 1 ]]; then
+    mkdir -p "$new_dir"
+    mv "$old_checkout" "$new_checkout"
+
+    tmp_record=$(mktemp "$new_dir/materialization.json.tmp.XXXXXX")
+    jq --arg root "$new_checkout" '.root = $root' "$record" > "$tmp_record"
+    mv "$tmp_record" "$new_record"
+
+    git -C "$source_repository_path" worktree repair "$new_checkout"
+
+    rm "$record"
+    rmdir "$old_dir/root"
+    rmdir "$old_dir"
+  fi
+  migrated=$((migrated + 1))
+done
+
+if [[ $apply -eq 1 ]]; then
+  rmdir "$old_root" 2>/dev/null || true
+  log "migrated $migrated workdir(s)"
+else
+  log "dry-run complete: $migrated workdir(s) would be migrated"
+fi