diff --git a/ui/goose2/justfile b/ui/goose2/justfile
index ae5832f43b..afcbf4fe10 100644
--- a/ui/goose2/justfile
+++ b/ui/goose2/justfile
@@ -1,6 +1,6 @@
-# Derive a stable port from the working directory so the same worktree
-# always gets the same port.
-vite_port := `python3 -c "import hashlib,os; h=int(hashlib.sha256(os.getcwd().encode()).hexdigest(),16); print(10000 + h % 55000)"`
+# Derive a stable default port from the working directory so the same worktree
+# usually gets the same port. Set VITE_PORT to override it.
+default_vite_port := `python3 -c "import hashlib,os; h=int(hashlib.sha256(os.getcwd().encode()).hexdigest(),16); print(10000 + h % 55000)"`
 
 # Default recipe
 default:
@@ -83,7 +83,8 @@ dev: setup
     #!/usr/bin/env bash
     set -euo pipefail
 
-    VITE_PORT={{ vite_port }}
+    DEFAULT_VITE_PORT={{ default_vite_port }}
+    VITE_PORT="${VITE_PORT:-$DEFAULT_VITE_PORT}"
     export VITE_PORT
     # Enable perf logs in the child `goose serve` process by default.
     # Override with e.g. RUST_LOG=info just dev to disable.
@@ -103,7 +104,7 @@ dev: setup
     else
         unset GOOSE_BIN
     fi
-    EXTRA_CONFIG_ARGS=(--config "{\"build\":{\"devUrl\":\"http://localhost:${VITE_PORT}\",\"beforeDevCommand\":{\"script\":\"cd ${PROJECT_DIR} && exec pnpm exec vite --port ${VITE_PORT} --strictPort\",\"cwd\":\".\",\"wait\":false}}}")
+    EXTRA_CONFIG_ARGS=(--config "{\"build\":{\"devUrl\":\"http://localhost:${VITE_PORT}\",\"beforeDevCommand\":{\"script\":\"exec ./scripts/start-dev-vite.sh ${VITE_PORT}\",\"cwd\":\"${PROJECT_DIR}\",\"wait\":false}}}")
 
     if [[ -n "${GOOSE_BIN:-}" ]]; then
         echo "Using local goose binary: ${GOOSE_BIN}"
@@ -140,11 +141,13 @@ dev-debug: setup
     #!/usr/bin/env bash
     set -euo pipefail
 
-    VITE_PORT={{ vite_port }}
+    DEFAULT_VITE_PORT={{ default_vite_port }}
+    VITE_PORT="${VITE_PORT:-$DEFAULT_VITE_PORT}"
     export VITE_PORT
     # Enable perf logs in the child `goose serve` process by default.
     # Override with e.g. RUST_LOG=info just dev-debug to disable.
     export RUST_LOG="${RUST_LOG:-perf=debug,info}"
+    PROJECT_DIR=$(pwd)
     REPO_ROOT=$(cd ../.. && pwd)
     DISTRO_DIR="$(pwd)/distro"
     if [[ -z "${GOOSE_DISTRO_DIR:-}" && -d "${DISTRO_DIR}" ]]; then
@@ -159,7 +162,7 @@ dev-debug: setup
     else
         unset GOOSE_BIN
     fi
-    EXTRA_CONFIG_ARGS=(--config "{\"build\":{\"devUrl\":\"http://localhost:${VITE_PORT}\",\"beforeDevCommand\":{\"script\":\"exec ./node_modules/.bin/vite --port ${VITE_PORT} --strictPort\",\"cwd\":\"..\",\"wait\":false}}}")
+    EXTRA_CONFIG_ARGS=(--config "{\"build\":{\"devUrl\":\"http://localhost:${VITE_PORT}\",\"beforeDevCommand\":{\"script\":\"exec ./scripts/start-dev-vite.sh ${VITE_PORT}\",\"cwd\":\"${PROJECT_DIR}\",\"wait\":false}}}")
 
     if [[ -n "${GOOSE_BIN:-}" ]]; then
         echo "Using local goose binary: ${GOOSE_BIN}"
@@ -231,7 +234,8 @@ kill branch="":
         TARGET_DIR="$WORKTREE_PATH/ui/goose2"
         VITE_PORT=$(python3 -c '{{ _port_cmd }}' "$TARGET_DIR")
     else
-        VITE_PORT={{ vite_port }}
+        DEFAULT_VITE_PORT={{ default_vite_port }}
+        VITE_PORT="${VITE_PORT:-$DEFAULT_VITE_PORT}"
     fi
 
     PID=$(lsof -ti :"$VITE_PORT" 2>/dev/null | head -1) || true
diff --git a/ui/goose2/scripts/start-dev-vite.sh b/ui/goose2/scripts/start-dev-vite.sh
new file mode 100755
index 0000000000..a28e1c0586
--- /dev/null
+++ b/ui/goose2/scripts/start-dev-vite.sh
@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+VITE_PORT="${1:-${VITE_PORT:-}}"
+if [[ -z "${VITE_PORT}" ]]; then
+    echo "VITE_PORT is required" >&2
+    exit 1
+fi
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"
+
+PID=$(lsof -ti :"${VITE_PORT}" 2>/dev/null | head -1 || true)
+if [[ -n "${PID}" ]]; then
+    PROC_ARGS="$(ps -p "${PID}" -o args= 2>/dev/null || true)"
+    PROC_CWD="$(lsof -a -p "${PID}" -d cwd -Fn 2>/dev/null | sed -n 's/^n//p' | head -1)"
+    if [[ "${PROC_CWD}" == "${PROJECT_DIR}" && "${PROC_ARGS}" == *"--port ${VITE_PORT} --strictPort"* ]]; then
+        echo "Reusing existing Goose2 Vite dev server on port ${VITE_PORT} (PID ${PID})"
+        exit 0
+    fi
+
+    PROC_NAME="$(ps -p "${PID}" -o comm= 2>/dev/null || true)"
+    echo "Port ${VITE_PORT} is already in use by '${PROC_NAME}' (PID ${PID})." >&2
+    echo "Run 'just goose2 kill' if it is a stale Goose2 dev server, or rerun with VITE_PORT=<free-port> just goose2 dev." >&2
+    exit 1
+fi
+
+cd "${PROJECT_DIR}"
+exec pnpm exec vite --port "${VITE_PORT}" --strictPort