Add bb.edn runner scripts and improve nREPL port handling

- bb.edn with compile/test/repl/nrepl/clean/fmt tasks
- nREPL checks .nrepl-port for existing server before starting
- Cleans up .nrepl-port on shutdown
- Add .nrepl-port to .gitignore

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -8,3 +8,4 @@ erl_crash.dump
 *.beam
 /tmp/
 .elixir_ls/
+.nrepl-port

bb.edn

@@ -0,0 +1,27 @@
+{:tasks
+ {compile {:doc  "Compile all .clje and .ex files"
+           :task (shell "mix compile")}
+
+  test    {:doc  "Run all tests"
+           :task (shell "mix test")}
+
+  test:trace {:doc  "Run all tests with trace output"
+              :task (shell "mix test --trace")}
+
+  repl    {:doc  "Start interactive CljElixir REPL"
+           :task (shell "rlwrap mix clje.repl")}
+
+  repl:basic {:doc  "Start REPL without rlwrap"
+              :task (shell "mix clje.repl")}
+
+  nrepl   {:doc  "Start nREPL server (random port)"
+           :task (shell "mix clje.nrepl")}
+
+  nrepl:port {:doc  "Start nREPL on port 7888"
+              :task (shell "mix clje.nrepl --port 7888")}
+
+  clean   {:doc  "Clean build artifacts"
+           :task (shell "mix clean")}
+
+  fmt     {:doc  "Format Elixir source files"
+           :task (shell "mix format")}}}

lib/mix/tasks/clje.nrepl.ex

@@ -8,16 +8,36 @@ defmodule Mix.Tasks.Clje.Nrepl do
       mix clje.nrepl --port 7888  # specific port
 
   Writes port to `.nrepl-port` file for editor auto-discovery.
+  Cleans up `.nrepl-port` on shutdown.
+
+  If `.nrepl-port` exists and a server is already listening on that port,
+  prints the existing port and exits rather than starting a duplicate.
   """
 
   use Mix.Task
 
   @shortdoc "Start a CljElixir nREPL server"
+  @nrepl_port_file ".nrepl-port"
 
   @impl Mix.Task
   def run(args) do
     {opts, _, _} = OptionParser.parse(args, strict: [port: :integer])
-    port = Keyword.get(opts, :port, 0)
+    requested_port = Keyword.get(opts, :port)
+
+    # Check for existing server via .nrepl-port
+    if requested_port == nil and File.exists?(@nrepl_port_file) do
+      case check_existing_server() do
+        {:ok, existing_port} ->
+          IO.puts("nREPL server already running on port #{existing_port}")
+          IO.puts("Connect with: nrepl://127.0.0.1:#{existing_port}")
+          System.halt(0)
+
+        :stale ->
+          File.rm(@nrepl_port_file)
+      end
+    end
+
+    port = requested_port || 0
 
     Mix.Task.run("compile")
     Mix.Task.run("app.start")
@@ -25,12 +45,43 @@ defmodule Mix.Tasks.Clje.Nrepl do
     {:ok, server} = CljElixir.NRepl.Server.start_link(port: port)
     actual_port = CljElixir.NRepl.Server.port(server)
 
-    File.write!(".nrepl-port", Integer.to_string(actual_port))
+    File.write!(@nrepl_port_file, Integer.to_string(actual_port))
+
+    # Clean up .nrepl-port on shutdown
+    cleanup_on_exit()
 
     IO.puts("nREPL server started on port #{actual_port} on host 127.0.0.1")
-    IO.puts("Port written to .nrepl-port")
+    IO.puts("Port written to #{@nrepl_port_file}")
     IO.puts("Press Ctrl+C to stop\n")
 
     Process.sleep(:infinity)
   end
+
+  defp check_existing_server do
+    with {:ok, content} <- File.read(@nrepl_port_file),
+         {port, ""} <- Integer.parse(String.trim(content)),
+         true <- port_alive?(port) do
+      {:ok, port}
+    else
+      _ -> :stale
+    end
+  end
+
+  defp port_alive?(port) do
+    case :gen_tcp.connect(~c"127.0.0.1", port, [:binary], 500) do
+      {:ok, socket} ->
+        :gen_tcp.close(socket)
+        true
+
+      {:error, _} ->
+        false
+    end
+  end
+
+  defp cleanup_on_exit do
+    # Trap exits so we can clean up the port file
+    System.at_exit(fn _status ->
+      File.rm(@nrepl_port_file)
+    end)
+  end
 end