diff --git a/popdoc/wasm/lib/eval.ex b/popdoc/wasm/lib/eval.ex
new file mode 100644
index 00000000..89a1aa02
--- /dev/null
+++ b/popdoc/wasm/lib/eval.ex
@@ -0,0 +1,95 @@
+defmodule PopdocWasm.Eval do
+  @moduledoc """
+  Evaluation helpers shared by eval blocks and the IEx terminal. Stateless:
+  callers own their binding + env (`PopdocWasm` keeps them in its GenServer
+  state) and thread them through each call.
+  """
+
+  @doc """
+  Evaluates the string `code` (possibly multi-line) IEx-style.
+
+  Returns:
+    * `:incomplete` - input ends mid-expression (missing `end`, unclosed
+      delimiter); nothing was evaluated. Same rule IEx uses.
+    * `{:ok, inspected, binding, env}`
+    * `{:error, error_map}` - the caller keeps its binding and env. Parse
+      errors carry an empty stacktrace.
+  """
+  def eval_string(code, binding, env, inspect_opts \\ []) do
+    with {:ok, quoted} <- parse_input(code) do
+      eval_quoted(quoted, binding, env, inspect_opts)
+    end
+  end
+
+  def eval_quoted(quoted, binding, env, inspect_opts \\ []) do
+    {value, new_binding, new_env} = Code.eval_quoted_with_env(quoted, binding, env)
+    {:ok, inspect(value, [charlists: :as_lists] ++ inspect_opts), new_binding, new_env}
+  rescue
+    err ->
+      {:error, exception_to_error_map(err, format_user_stacktrace(__STACKTRACE__))}
+  catch
+    kind, reason ->
+      {:error,
+       %{
+         kind: kind,
+         type: nil,
+         message: inspect(reason),
+         stacktrace: format_user_stacktrace(__STACKTRACE__)
+       }}
+  end
+
+  def fresh_env(file) do
+    %Macro.Env{
+      __ENV__
+      | file: file,
+        line: 1,
+        module: nil,
+        function: nil
+    }
+  end
+
+  defp parse_input(code) do
+    {:ok, Code.string_to_quoted!(ensure_trailing_newline(code))}
+  rescue
+    _ in TokenMissingError -> :incomplete
+    err -> {:error, exception_to_error_map(err, "")}
+  end
+
+  defp ensure_trailing_newline(code) do
+    if String.ends_with?(code, "\n"), do: code, else: code <> "\n"
+  end
+
+  defp exception_to_error_map(err, stacktrace) do
+    %{
+      kind: :error,
+      type: inspect(err.__struct__),
+      message: Exception.message(err),
+      stacktrace: stacktrace
+    }
+  end
+
+  defp format_user_stacktrace(stacktrace) do
+    frames =
+      stacktrace
+      |> Enum.take_while(fn
+        {:elixir, :eval_external_handler, _, _} -> false
+        _ -> true
+      end)
+      |> Enum.reject(fn
+        {:erlang, :apply, _, _} -> true
+        _ -> false
+      end)
+
+    if length(frames) >= 2 do
+      frames
+      |> Exception.format_stacktrace()
+      |> String.split("\n")
+      |> Enum.map_join("\n", fn
+        "    " <> rest -> rest
+        line -> line
+      end)
+    else
+      ""
+    end
+  end
+end
diff --git a/popdoc/wasm/lib/wasm.ex b/popdoc/wasm/lib/wasm.ex
index fb6d789b..bb79fb29 100644
--- a/popdoc/wasm/lib/wasm.ex
+++ b/popdoc/wasm/lib/wasm.ex
@@ -3,10 +3,12 @@ defmodule PopdocWasm do
 
   import Popcorn.Wasm, only: [is_wasm_message: 1]
   alias Popcorn.Wasm
+  alias PopdocWasm.Eval
 
   @process_name :main
   @ellipsis_sentinel :__popdoc_ellipsis__
   @snippet_max_len 40
+  @syntax_colors IO.ANSI.syntax_colors()
 
   def start_link(args) do
     GenServer.start_link(__MODULE__, args, name: @process_name)
@@ -14,10 +16,12 @@ defmodule PopdocWasm do
 
   @impl true
   def init(_args) do
+    # Evaluated user code runs in this process; a crashing linked process
+    # (spawn_link, Task.async) must deliver an exit message instead of
+    # killing the session with all its bindings.
+    Process.flag(:trap_exit, true)
     Wasm.ready(@process_name)
-    # TODO: needed?
-    :application.set_env(:elixir, :ansi_enabled, false)
-    {:ok, %{sessions: %{}}}
+    {:ok, %{sessions: %{}, iex: nil}}
   end
 
   @impl true
@@ -44,7 +48,7 @@ defmodule PopdocWasm do
             }
           end)
 
-        session = %{exprs: exprs, binding: [], env: fresh_env()}
+        session = %{exprs: exprs, binding: [], env: Eval.fresh_env("playground")}
         new_state = put_in(state.sessions[block_id], session)
         {:resolve, %{expressions: expressions}, new_state}
 
@@ -56,7 +60,7 @@ defmodule PopdocWasm do
   defp handle_wasm({:wasm_call, ["eval_one", block_id, index]}, state) when index >= 0 do
     with {:ok, session} <- Map.fetch(state.sessions, block_id),
          {_source, quoted} <- Enum.at(session.exprs, index) do
-      case eval_quoted(quoted, session.binding, session.env) do
+      case Eval.eval_quoted(quoted, session.binding, session.env) do
         {:ok, result, new_binding, new_env} ->
           bindings = diff_binding(session.binding, new_binding)
           updated = %{session | binding: new_binding, env: new_env}
@@ -72,12 +76,45 @@ defmodule PopdocWasm do
     end
   end
 
+  # Sent on SPA navigation: eval-block sessions never outlive their page, and
+  # a run that spans the navigation gets a clean "no active session" reject.
+  defp handle_wasm({:wasm_call, ["clear_sessions"]}, state) do
+    {:resolve, %{}, %{state | sessions: %{}}}
+  end
+
+  # Idempotent: re-calls (launcher, markdown clicks) must not wipe bindings.
+  defp handle_wasm({:wasm_call, ["start_iex"]}, state) do
+    {:resolve, %{}, ensure_iex(state)}
+  end
+
+  defp handle_wasm({:wasm_call, ["iex_eval", code]}, state) when is_binary(code) do
+    state = ensure_iex(state)
+
+    # Terminal-only path, so results carry IEx-style ANSI syntax colors;
+    # eval blocks keep plain inspect via eval_one.
+    case Eval.eval_string(code, state.iex.binding, state.iex.env, syntax_colors: @syntax_colors) do
+      :incomplete ->
+        {:resolve, %{status: "incomplete"}, state}
+
+      {:ok, result, binding, env} ->
+        {:resolve, %{status: "ok", result: result}, %{state | iex: %{binding: binding, env: env}}}
+
+      {:error, error_map} ->
+        {:resolve, %{status: "error", error: error_map}, state}
+    end
+  end
+
   defp handle_wasm({:wasm_call, message}, state) do
     {:reject, "unknown wasm call: #{inspect(message)}", state}
   end
 
   defp handle_wasm({:wasm_cast, _message}, state), do: state
 
+  defp ensure_iex(%{iex: nil} = state),
+    do: %{state | iex: %{binding: [], env: Eval.fresh_env("iex")}}
+
+  defp ensure_iex(state), do: state
+
   defp diff_binding(old, new) do
     old_map = Map.new(old)
 
@@ -86,16 +123,6 @@ defmodule PopdocWasm do
     end
   end
 
-  defp fresh_env do
-    %Macro.Env{
-      __ENV__
-      | file: "playground",
-        line: 1,
-        module: nil,
-        function: nil
-    }
-  end
-
   defp parse(code) do
     quoted = Code.string_to_quoted!(code)
 
@@ -110,54 +137,6 @@ defmodule PopdocWasm do
     error -> {:error, Exception.format(:error, error)}
   end
 
-  defp eval_quoted(quoted, binding, env) do
-    {value, new_binding, new_env} = Code.eval_quoted_with_env(quoted, binding, env)
-    {:ok, inspect(value, charlists: :as_lists), new_binding, new_env}
-  rescue
-    err ->
-      {:error,
-       %{
-         kind: :error,
-         type: inspect(err.__struct__),
-         message: Exception.message(err),
-         stacktrace: format_user_stacktrace(__STACKTRACE__)
-       }}
-  catch
-    kind, reason ->
-      {:error,
-       %{
-         kind: kind,
-         type: nil,
-         message: inspect(reason),
-         stacktrace: format_user_stacktrace(__STACKTRACE__)
-       }}
-  end
-
-  defp format_user_stacktrace(stacktrace) do
-    frames =
-      stacktrace
-      |> Enum.take_while(fn
-        {:elixir, :eval_external_handler, _, _} -> false
-        _ -> true
-      end)
-      |> Enum.reject(fn
-        {:erlang, :apply, _, _} -> true
-        _ -> false
-      end)
-
-    if length(frames) >= 2 do
-      frames
-      |> Exception.format_stacktrace()
-      |> String.split("\n")
-      |> Enum.map_join("\n", fn
-        "    " <> rest -> rest
-        line -> line
-      end)
-    else
-      ""
-    end
-  end
-
   defp start_line({_, meta, _}) when is_list(meta), do: Keyword.get(meta, :line, 1)
   defp start_line(_), do: 1
 
diff --git a/popdoc/wasm/test/eval_test.exs b/popdoc/wasm/test/eval_test.exs
new file mode 100644
index 00000000..273ba5f8
--- /dev/null
+++ b/popdoc/wasm/test/eval_test.exs
@@ -0,0 +1,99 @@
+defmodule PopdocWasm.EvalTest do
+  use ExUnit.Case, async: true
+
+  alias PopdocWasm.Eval
+
+  defp eval(code, binding \\ [], opts \\ []) do
+    Eval.eval_string(code, binding, Eval.fresh_env("test"), opts)
+  end
+
+  describe "incomplete input" do
+    test "dangling operator" do
+      assert :incomplete = eval("1 +")
+    end
+
+    test "missing end" do
+      assert :incomplete = eval("defmodule Foo do")
+    end
+
+    test "unclosed list" do
+      assert :incomplete = eval("[1, 2")
+    end
+
+    test "unclosed string" do
+      assert :incomplete = eval(~s("abc))
+    end
+
+    test "heredoc opener without trailing newline" do
+      assert :incomplete = eval(~s(@doc """))
+      assert :incomplete = eval(~s(x = """))
+    end
+
+    test "completed heredoc evaluates" do
+      assert {:ok, result, _, _} = eval("x = \"\"\"\nhello\n\"\"\"")
+      assert result =~ "hello"
+    end
+  end
+
+  describe "parse errors" do
+    test "syntax error maps to error with empty stacktrace" do
+      assert {:error, error} = eval("1 )")
+      assert error.type in ["SyntaxError", "MismatchedDelimiterError"]
+      assert error.stacktrace == ""
+    end
+  end
+
+  describe "evaluation" do
+    test "simple expression" do
+      assert {:ok, "2", _, _} = eval("1 + 1")
+    end
+
+    test "bindings persist across evals" do
+      {:ok, "41", binding, env} = eval("x = 41")
+      assert {:ok, "42", _, _} = Eval.eval_string("x + 1", binding, env)
+    end
+
+    test "rebinding works" do
+      {:ok, _, binding, env} = eval("x = 1")
+      {:ok, _, binding, env} = Eval.eval_string("x = 2", binding, env)
+      assert {:ok, "2", _, _} = Eval.eval_string("x", binding, env)
+    end
+
+    test "inspect opts colorize the result" do
+      assert {:ok, result, _, _} = eval(":ok", [], syntax_colors: IO.ANSI.syntax_colors())
+      assert result =~ "\e["
+      assert result =~ ":ok"
+    end
+
+    test "multi-expression text returns the last value" do
+      assert {:ok, "2", _, _} = eval("a = 1\na + 1")
+    end
+
+    test "continuation completes once the input closes" do
+      assert :incomplete = eval("if true do")
+      assert :incomplete = eval("if true do\n1")
+      assert {:ok, "1", _, _} = eval("if true do\n1\nend")
+    end
+  end
+
+  describe "runtime errors" do
+    test "exception maps to error with type" do
+      assert {:error, error} = eval("1 / 0")
+      assert error.type == "ArithmeticError"
+      assert error.kind == :error
+    end
+
+    test "bindings survive a failed eval" do
+      {:ok, _, binding, env} = eval("x = 5")
+      assert {:error, _} = Eval.eval_string("raise \"boom\"", binding, env)
+      assert {:ok, "5", _, _} = Eval.eval_string("x", binding, env)
+    end
+
+    test "throw maps to kind :throw" do
+      assert {:error, error} = eval("throw :ball")
+      assert error.kind == :throw
+      assert error.type == nil
+      assert error.message == ":ball"
+    end
+  end
+end
diff --git a/popdoc/wasm/test/test_helper.exs b/popdoc/wasm/test/test_helper.exs
new file mode 100644
index 00000000..869559e7
--- /dev/null
+++ b/popdoc/wasm/test/test_helper.exs
@@ -0,0 +1 @@
+ExUnit.start()