diff --git a/.gitignore b/.gitignore
index bc03f6e..70c4150 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,3 +7,6 @@ site/node_modules/
 site/dist/
 .DS_Store
 .claude/launch.json
+
+# Per-worktree dev port slot (scripts/dev-port.sh) — never commit a lane's slot.
+.dev-port
diff --git a/orca.yaml b/orca.yaml
index 73de412..12969ed 100644
--- a/orca.yaml
+++ b/orca.yaml
@@ -55,3 +55,11 @@ defaultTabs:
     command: |-
         g="$(git rev-parse --git-dir 2>/dev/null)"; [ "$g" = "$(git rev-parse --git-common-dir 2>/dev/null)" ] || { i=0; while [ ! -e "$g/orca-setup-done" ] && [ "$i" -lt 150 ]; do sleep 1; i=$((i+1)); done; [ -e "$g/orca-setup-done" ] || echo "orca-tab: gave up waiting ${i}s for setup - it may have failed or been skipped"; }; bun run test
     color: "#059669"
+  # On-demand: resolves this lane's port and prints how to serve + look at the
+  # roadmap view. Boots nothing. `nextup serve` defaults to 4177, which the mac
+  # holds permanently via the dev.hansenexus.nextup-serve LaunchAgent, so a lane
+  # must not use the default.
+  - title: preview
+    command: |-
+        g="$(git rev-parse --git-dir 2>/dev/null)"; [ "$g" = "$(git rev-parse --git-common-dir 2>/dev/null)" ] || { i=0; while [ ! -e "$g/orca-setup-done" ] && [ "$i" -lt 150 ]; do sleep 1; i=$((i+1)); done; [ -e "$g/orca-setup-done" ] || echo "orca-tab: gave up waiting ${i}s for setup - it may have failed or been skipped"; }; echo "this lane: $(bash scripts/dev-port.sh --url)"; echo; echo 'serve it:  bun cli.ts serve --port $(bash scripts/dev-port.sh)'; echo 'open it:   orca tab create --worktree current --url "$(bash scripts/dev-port.sh --url)"'; echo 'look:      orca snapshot   |   orca screenshot --format png'; echo; exec "${SHELL:-bash}" -i
+    color: "#0ea5e9"
diff --git a/scripts/dev-port.sh b/scripts/dev-port.sh
new file mode 100755
index 0000000..84afb32
--- /dev/null
+++ b/scripts/dev-port.sh
@@ -0,0 +1,75 @@
+#!/usr/bin/env bash
+# dev-port.sh — this worktree's dev port.
+#
+# The dev server binds a fixed port (4177). Run two Orca lanes at once and the
+# second one either dies on EADDRINUSE or, worse, does not: the first lane
+# already owns the port, so the browser reaches THAT server and you review one
+# lane's code while looking at another's output. It fails green.
+#
+# Each worktree gets a slot (0..15) from a stable hash of its absolute path;
+# the port is `base + slot * 100`. The main checkout is always slot 0, so its
+# port stays exactly 4177 and nothing changes for anyone not using worktrees.
+#
+# A worktree's own prior claim (recorded in its `.dev-port`) wins over a fresh
+# hash, so removing an unrelated sibling cannot silently move a surviving
+# worktree to a different port between two runs.
+#
+# Here the collision is not just lane-vs-lane: the mac runs `nextup serve` on
+# 4177 permanently as the LaunchAgent dev.hansenexus.nextup-serve (verified
+# holding the port on 2026-09-09), so a lane using the default would fight the
+# machine's own long-running server. Slot 0 still resolves 4177 because the main
+# checkout is not where lanes run.
+#
+# Scope: isolates lanes of THIS repo from each other, not across repos.
+#
+#   scripts/dev-port.sh          # bare port, for `--port $(…)`
+#   scripts/dev-port.sh --url    # http://localhost:<port>
+set -euo pipefail
+
+BASE=4177
+MAX_SLOTS=16
+STRIDE=100
+
+root="$(git rev-parse --show-toplevel)"
+
+read_slot() {  # $1 = worktree toplevel
+  local v
+  v="$(cat "$1/.dev-port" 2>/dev/null || true)"
+  case "$v" in
+    ''|*[!0-9]*) return 1 ;;
+    *) [ "$v" -lt "$MAX_SLOTS" ] && printf '%s' "$v" || return 1 ;;
+  esac
+}
+
+if [ "$(git rev-parse --git-dir)" = "$(git rev-parse --git-common-dir)" ]; then
+  slot=0                                   # main checkout
+else
+  claimed=" 0 "
+  while IFS= read -r line; do
+    case "$line" in worktree\ *) ;; *) continue ;; esac
+    top="${line#worktree }"
+    [ "$top" = "$root" ] && continue
+    s="$(read_slot "$top" || true)"
+    [ -n "$s" ] && claimed="$claimed$s "
+  done < <(git worktree list --porcelain)
+
+  own="$(read_slot "$root" || true)"
+  if [ -n "$own" ] && [ "$own" -gt 0 ] && [[ "$claimed" != *" $own "* ]]; then
+    slot="$own"
+  else
+    start="$(printf '%s' "$root" | cksum | awk -v m="$MAX_SLOTS" '{print $1 % m}')"
+    slot=""
+    for i in $(seq 0 $((MAX_SLOTS - 1))); do
+      cand=$(((start + i) % MAX_SLOTS))
+      if [[ "$claimed" != *" $cand "* ]]; then slot="$cand"; break; fi
+    done
+    if [ -z "$slot" ]; then
+      echo "dev-port: all $MAX_SLOTS worktree slots are taken — remove an unused worktree" >&2
+      exit 1
+    fi
+  fi
+  printf '%s\n' "$slot" > "$root/.dev-port"
+fi
+
+port=$((BASE + slot * STRIDE))
+if [ "${1:-}" = "--url" ]; then printf 'http://localhost:%s\n' "$port"; else printf '%s\n' "$port"; fi