diff --git a/scripts/post-create.sh b/scripts/post-create.sh
index 431e944d74..7ca17551aa 100755
--- a/scripts/post-create.sh
+++ b/scripts/post-create.sh
@@ -11,15 +11,5 @@ if [[ -z "$backend_port" || -z "$frontend_port" ]]; then
   exit 1
 fi
 
-cat > .env.local <<EOF
-BACKEND_PORT=$backend_port
-FRONTEND_PORT=$frontend_port
-REMOTE=http://localhost:$backend_port
-EOF
-
-if [[ -n "${CARGO_FEATURES:-}" ]]; then
-  echo "CARGO_FEATURES=$CARGO_FEATURES" >> .env.local
-fi
-
-echo "Created .env.local with ports: backend=$backend_port, frontend=$frontend_port"
+wm_write_env_local "$(pwd)" "$backend_port" "$frontend_port"
 wm_shared_post_create "$(pwd)"
diff --git a/scripts/worktree-common.sh b/scripts/worktree-common.sh
index 672b9f9f65..fd741f6312 100755
--- a/scripts/worktree-common.sh
+++ b/scripts/worktree-common.sh
@@ -13,6 +13,65 @@ wm_main_repo_root() {
   cd "$(git -C "$repo_root" rev-parse --git-common-dir 2>/dev/null)/.." && pwd
 }
 
+wm_port_in_use() {
+  lsof -nP -iTCP:"$1" -sTCP:LISTEN &>/dev/null
+}
+
+# Prints "<backend_port> <frontend_port>" for the lowest free slot. Slots are read from
+# each worktree's .env.local rather than from position in `git worktree list`: removing a
+# worktree in the middle would otherwise hand its slot to a new one while a live
+# neighbour still listens on those ports. Slot 0 belongs to the main checkout.
+wm_assign_ports() {
+  local repo_root=$1
+  local slot=${WM_SLOT:-}
+  local used_slots=() wt_path backend_port frontend_port bp
+
+  if [[ -z "$slot" ]]; then
+    while IFS= read -r wt_path; do
+      [[ "$wt_path" == "$repo_root" ]] && continue
+      [[ -f "$wt_path/.env.local" ]] || continue
+      bp=$(grep '^BACKEND_PORT=' "$wt_path/.env.local" | cut -d= -f2 || true)
+      if [[ -n "$bp" && "$bp" -gt 8000 ]]; then
+        used_slots+=("$(( (bp - 8000) / 10 ))")
+      fi
+    done < <(git -C "$repo_root" worktree list --porcelain | sed -n 's/^worktree //p')
+
+    slot=1
+    while [[ " ${used_slots[*]:-} " == *" $slot "* ]]; do
+      ((slot++))
+    done
+    echo "Auto-assigned slot $slot (used: ${used_slots[*]:-none})" >&2
+  fi
+
+  backend_port=$((8000 + slot * 10))
+  frontend_port=$((3000 + slot * 10))
+
+  if wm_port_in_use "$backend_port" || wm_port_in_use "$frontend_port"; then
+    echo "WARNING: slot $slot ports ($backend_port/$frontend_port) already in use" >&2
+  fi
+
+  printf '%s %s\n' "$backend_port" "$frontend_port"
+}
+
+wm_write_env_local() {
+  local repo_root=$1
+  local backend_port=$2
+  local frontend_port=$3
+  local env_file="${repo_root}/.env.local"
+
+  cat > "$env_file" <<EOF
+BACKEND_PORT=$backend_port
+FRONTEND_PORT=$frontend_port
+REMOTE=http://localhost:$backend_port
+EOF
+
+  if [[ -n "${CARGO_FEATURES:-}" ]]; then
+    echo "CARGO_FEATURES=$CARGO_FEATURES" >> "$env_file"
+  fi
+
+  echo "Created .env.local with ports: backend=$backend_port, frontend=$frontend_port"
+}
+
 wm_setup_database() {
   local repo_root=$1
   local env_file=$2
diff --git a/scripts/worktree-env b/scripts/worktree-env
index e45daba75b..390a12fd66 100755
--- a/scripts/worktree-env
+++ b/scripts/worktree-env
@@ -3,54 +3,6 @@ set -euo pipefail
 
 source "$(dirname "${BASH_SOURCE[0]}")/worktree-common.sh"
 
-port_in_use() {
-  lsof -nP -iTCP:"$1" -sTCP:LISTEN &>/dev/null
-}
-
-if [[ -z "${WM_SLOT:-}" ]]; then
-  # Scan .env.local files of existing worktrees to find which slots are claimed,
-  # then pick the lowest free slot. This avoids collisions when worktrees are
-  # removed and new ones created (position-based indexing would re-use slots
-  # still held by surviving worktrees).
-  used_slots=()
-  current_dir="$(pwd)"
-  while IFS= read -r wt_path; do
-    [[ "$wt_path" == "$current_dir" ]] && continue
-    if [[ -f "$wt_path/.env.local" ]]; then
-      bp=$(grep '^BACKEND_PORT=' "$wt_path/.env.local" | cut -d= -f2 || true)
-      if [[ -n "$bp" && "$bp" -gt 8000 ]]; then
-        used_slots+=("$(( (bp - 8000) / 10 ))")
-      fi
-    fi
-  done < <(git worktree list --porcelain | sed -n 's/^worktree //p')
-
-  # Find lowest available slot (slot 0 = 8000/3000 is reserved for main)
-  WM_SLOT=1
-  while [[ " ${used_slots[*]:-} " == *" $WM_SLOT "* ]]; do
-    ((WM_SLOT++))
-  done
-  echo "Auto-assigned slot $WM_SLOT (used: ${used_slots[*]:-none})"
-fi
-
-# Slot-based: predictable ports for SSH forwarding
-# Slot 0 = 8000/3000, slot 1 = 8010/3010, slot 2 = 8020/3020, etc.
-backend_port=$((8000 + WM_SLOT * 10))
-frontend_port=$((3000 + WM_SLOT * 10))
-
-if port_in_use "$backend_port" || port_in_use "$frontend_port"; then
-  echo "WARNING: Slot $WM_SLOT ports ($backend_port/$frontend_port) already in use" >&2
-fi
-
-# Generate .env.local with port overrides
-cat > .env.local <<EOF
-BACKEND_PORT=$backend_port
-FRONTEND_PORT=$frontend_port
-REMOTE=http://localhost:$backend_port
-EOF
-
-if [[ -n "${CARGO_FEATURES:-}" ]]; then
-  echo "CARGO_FEATURES=$CARGO_FEATURES" >> .env.local
-fi
-
-echo "Created .env.local with ports: backend=$backend_port, frontend=$frontend_port"
+read -r backend_port frontend_port < <(wm_assign_ports "$(pwd)")
+wm_write_env_local "$(pwd)" "$backend_port" "$frontend_port"
 wm_shared_post_create "$(pwd)"