fix: resolve 10 dialyzer warnings in new modules

- Policy: suppress MapSet opaque type warnings with @dialyzer [:no_opaque]
- Tool.Behaviour: widen metadata/0 callback type to map() for extra keys
- Transcript: remove redundant nil fallback on extract_text/1 return

Author: nyo16

lib/nous/permissions.ex

@@ -1,4 +1,7 @@
 defmodule Nous.Permissions do
+  # MapSet is opaque — suppress contract_with_opaque for functions returning Policy structs
+  @dialyzer [:no_opaque]
+
   @moduledoc """
   Tool-level permission policy engine.
 

lib/nous/permissions/policy.ex

@@ -30,9 +30,9 @@ defmodule Nous.Permissions.Policy do
   @type mode :: :default | :permissive | :strict
 
   @type t :: %__MODULE__{
-          deny_names: MapSet.t(String.t()),
+          deny_names: MapSet.t(),
           deny_prefixes: [String.t()],
-          approval_required: MapSet.t(String.t()),
+          approval_required: MapSet.t(),
           mode: mode()
         }
 end

lib/nous/tool/behaviour.ex

@@ -108,11 +108,7 @@ defmodule Nous.Tool.Behaviour do
       }
 
   """
-  @callback metadata() :: %{
-              name: String.t(),
-              description: String.t(),
-              parameters: map()
-            }
+  @callback metadata() :: map()
 
   @doc """
   Return the tool's schema definition for introspection.

lib/nous/transcript.ex

@@ -299,7 +299,7 @@ defmodule Nous.Transcript do
       messages
       |> Enum.map(fn msg ->
         role = msg.role || :unknown
-        text = Message.extract_text(msg) || ""
+        text = Message.extract_text(msg)
         preview = text |> String.slice(0..100) |> String.replace("\n", " ")
         "  [#{role}] #{preview}"
       end)