Phase 8: REPL, printing, source maps, and nREPL server

- IPrintWithWriter protocol + CljElixir.Printer module with pr-str,
  print-str, pr, prn for all BEAM types (EDN-like output)
- Source-mapped error messages: line/col metadata from reader now
  propagated through transformer into Elixir AST for accurate error
  locations in .clje files
- Interactive REPL (mix clje.repl) with multi-line input detection,
  history, bindings persistence, and pr-str formatted output
- nREPL server (mix clje.nrepl) with TCP transport, Bencode wire
  protocol, session management, and core operations (clone, close,
  eval, describe, ls-sessions, load-file, interrupt, completions).
  Writes .nrepl-port for editor auto-discovery.

92 new tests (699 total, 0 failures).

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

lib/clj_elixir/nrepl/handler.ex

@@ -0,0 +1,110 @@
+defmodule CljElixir.NRepl.Handler do
+  @moduledoc "Handles nREPL protocol messages."
+
+  alias CljElixir.NRepl.SessionManager
+
+  def handle(msg, session_manager) do
+    op = Map.get(msg, "op")
+    id = Map.get(msg, "id", "unknown")
+    session = Map.get(msg, "session")
+
+    case op do
+      "clone" -> handle_clone(id, session, session_manager)
+      "close" -> handle_close(id, session, session_manager)
+      "eval" -> handle_eval(msg, id, session, session_manager)
+      "describe" -> handle_describe(id, session)
+      "ls-sessions" -> handle_ls_sessions(id, session_manager)
+      "load-file" -> handle_load_file(msg, id, session, session_manager)
+      "interrupt" -> handle_interrupt(id, session)
+      "completions" -> handle_completions(msg, id, session)
+      _ -> [%{"id" => id, "session" => session || "", "status" => ["done", "error", "unknown-op"]}]
+    end
+  end
+
+  defp handle_clone(id, _session, manager) do
+    new_id = SessionManager.create_session(manager)
+    [%{"id" => id, "new-session" => new_id, "status" => ["done"]}]
+  end
+
+  defp handle_close(id, session, manager) do
+    SessionManager.close_session(manager, session)
+    [%{"id" => id, "session" => session, "status" => ["done"]}]
+  end
+
+  defp handle_eval(msg, id, session, manager) do
+    code = Map.get(msg, "code", "")
+
+    # Capture stdout inside the Agent process where eval actually runs
+    {output, result} = SessionManager.eval_with_capture(manager, session, code)
+
+    responses = []
+
+    # Send stdout if any
+    responses =
+      if output != "" do
+        responses ++ [%{"id" => id, "session" => session, "out" => output}]
+      else
+        responses
+      end
+
+    # Send value or error
+    responses =
+      case result do
+        {:ok, value} ->
+          responses ++ [%{"id" => id, "session" => session, "value" => value, "ns" => "user"}]
+
+        {:error, error} ->
+          responses ++
+            [%{"id" => id, "session" => session, "err" => error, "status" => ["eval-error"]}]
+      end
+
+    # Send done
+    responses ++ [%{"id" => id, "session" => session, "status" => ["done"]}]
+  end
+
+  defp handle_describe(id, session) do
+    [
+      %{
+        "id" => id,
+        "session" => session || "",
+        "status" => ["done"],
+        "ops" => %{
+          "clone" => %{},
+          "close" => %{},
+          "eval" => %{},
+          "describe" => %{},
+          "ls-sessions" => %{},
+          "load-file" => %{},
+          "interrupt" => %{},
+          "completions" => %{}
+        },
+        "versions" => %{
+          "clj-elixir" => %{"major" => 0, "minor" => 1, "incremental" => 0},
+          "nrepl" => %{"major" => 1, "minor" => 0, "incremental" => 0}
+        }
+      }
+    ]
+  end
+
+  defp handle_ls_sessions(id, manager) do
+    sessions = SessionManager.list_sessions(manager)
+    [%{"id" => id, "sessions" => sessions, "status" => ["done"]}]
+  end
+
+  defp handle_load_file(msg, id, session, manager) do
+    code = Map.get(msg, "file", "")
+    handle_eval(Map.put(msg, "code", code), id, session, manager)
+  end
+
+  defp handle_interrupt(id, session) do
+    # Not truly implemented -- just acknowledge
+    [%{"id" => id, "session" => session, "status" => ["done"]}]
+  end
+
+  defp handle_completions(msg, id, session) do
+    _prefix = Map.get(msg, "prefix", "")
+    # Basic completions -- return empty for now, can be extended later
+    [%{"id" => id, "session" => session || "", "completions" => [], "status" => ["done"]}]
+  end
+
+end