diff --git a/AGENTS.md b/AGENTS.md
index 550c934bce..7a4769e558 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -64,9 +64,9 @@ they set disjoint environment variables, so check which one you are in:
 
 See `backend/AGENTS.md` to restart the backend with different cargo features. Under herdr, `herdr
 --skill` prints a full reference for inspecting and driving panes and agents, and the plugins that
-provision worktrees live in `windmill-labs/windmill-herdr` — clone it and run `./setup.sh` to
-install them and the keybindings they need. The commands below are for a plain checkout with
-nothing running.
+provision worktrees live in the private `windmill-labs/windmill-herdr` — clone it and run
+`./setup.sh` to install them and the keybindings they need. The commands below are for a plain
+checkout with nothing running.
 
 - **Backend**: `cargo run` from `backend/` (API at http://localhost:8000)
 - **Frontend**: `REMOTE=http://localhost:8000 npm run dev` from `frontend/` (port 3000+)
@@ -78,9 +78,8 @@ nothing running.
 ### Per-worktree ports and database
 
 **`.env.local` in the worktree root is the portable answer** — `BACKEND_PORT`,
-`FRONTEND_PORT`, `REMOTE`, `DATABASE_URL`, `CARGO_FEATURES`, `WM_DB_NAME`. Both managers write it
-through the same helper (`wm_write_env_local` in `scripts/worktree-common.sh`), so it is correct
-whichever one you are in, and it is readable despite the name.
+`FRONTEND_PORT`, `REMOTE`, `DATABASE_URL`, `CARGO_FEATURES`, `WM_DB_NAME`. Both managers write
+those fields, so it is correct whichever one you are in, and it is readable despite the name.
 
 webmux additionally writes `$(git rev-parse --git-dir)/webmux/runtime.env`, which every pane
 sources at startup and which carries the extras `.env.local` lacks: `WEBMUX_*`, `WM_CLONE_DB`,
@@ -98,11 +97,12 @@ opt-in via `WM_CLONE_DB` (in `.webmux.yaml` under webmux, or the `windmill.workt
 
 The database is named after the **worktree directory, not the branch** (`scripts/worktree-common.sh`):
 `windmill_` + the directory basename with `-` → `_`, which Postgres then truncates at 63
-characters. Branch `hugo/win-2340-ai-agent-evals-standalone-agent-runs-and-eval-datasets` sits in
-a worktree directory named `win-2340-…`, so its database is
-`windmill_win_2340_ai_agent_evals_standalone_agent_runs_and_eval` — no `hugo_`, and the tail
-chopped. Take `WM_DB_NAME` from `runtime.env` instead of reconstructing the name. Read those, or
-discover from what is already running:
+characters. The two managers lay worktrees out differently, so the same branch lands in different
+directories and therefore different databases: under webmux, branch
+`hugo/win-2340-ai-agent-evals-standalone-agent-runs-and-eval-datasets` sits in a directory named
+`win-2340-…`, so its database is `windmill_win_2340_ai_agent_evals_standalone_agent_runs_and_eval`
+— no `hugo_`, and the tail chopped. Take `WM_DB_NAME` from `.env.local` instead of reconstructing
+the name. Read that, or discover from what is already running:
 
 ```bash
 psql postgres://postgres:changeme@localhost:5432/postgres -tAc \
diff --git a/scripts/worktree-common.sh b/scripts/worktree-common.sh
index fd741f6312..41d4ed109e 100755
--- a/scripts/worktree-common.sh
+++ b/scripts/worktree-common.sh
@@ -13,46 +13,8 @@ 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"
-}
-
+# Written by both worktree entry points — `worktree-env` by hand, `post-create.sh` from the
+# webmux hook — and read by agents to find their own ports, so the two must not drift.
 wm_write_env_local() {
   local repo_root=$1
   local backend_port=$2
diff --git a/scripts/worktree-env b/scripts/worktree-env
index 390a12fd66..1977eae470 100755
--- a/scripts/worktree-env
+++ b/scripts/worktree-env
@@ -3,6 +3,43 @@ set -euo pipefail
 
 source "$(dirname "${BASH_SOURCE[0]}")/worktree-common.sh"
 
-read -r backend_port frontend_port < <(wm_assign_ports "$(pwd)")
+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/$frontend_port) already in use" >&2
+fi
+
 wm_write_env_local "$(pwd)" "$backend_port" "$frontend_port"
 wm_shared_post_create "$(pwd)"