fix(presentation): collapse multi-line colset descrs in mermaid output

`Macro.to_string` returns multi-line output for composite descrs (maps,
nested tuples), but mermaid's `%%` only comments a single line. Trailing
lines escape the comment block and break the parser, e.g.:

    Parse error on line 2:
    ...flowchart TB  name: binary(),  realm: r
    ----------------------^
    Expecting 'SEMI', 'NEWLINE', 'EOF', ..., got 'NODE_STRING'

Collapse whitespace runs to a single space so the colset descr always
fits on one line.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: fahchen

lib/coloured_flow/definition/presentation/presentation.ex

@@ -49,7 +49,17 @@ defmodule ColouredFlow.Definition.Presentation do
   defp to_mermaid_colour_set(%ColourSet{name: name, type: type}) do
     alias ColouredFlow.Definition.ColourSet.Descr
 
-    "%% colset #{compose_call(name)} :: #{type |> Descr.to_quoted() |> Macro.to_string()}"
+    # `Macro.to_string` may return multi-line output for composite descrs
+    # (maps, nested tuples). Mermaid's `%%` only comments a single line, so
+    # trailing lines escape the comment and break the parser. Collapse
+    # whitespace runs to a single space so the colset descr fits on one line.
+    rendered =
+      type
+      |> Descr.to_quoted()
+      |> Macro.to_string()
+      |> String.replace(~r/\s+/u, " ")
+
+    "%% colset #{compose_call(name)} :: #{rendered}"
   end
 
   defp to_mermaid_place(%Place{name: name, colour_set: colour_set}) do

test/coloured_flow/definition/presentation_test.exs

@@ -1,6 +1,9 @@
 defmodule ColouredFlow.Definition.PresentationTest do
   use ExUnit.Case, async: true
 
+  alias ColouredFlow.Definition.ColourSet
+  alias ColouredFlow.Definition.ColouredPetriNet
+  alias ColouredFlow.Definition.Place
   alias ColouredFlow.Definition.Presentation
 
   import ColouredFlow.CpnetBuilder
@@ -80,6 +83,33 @@ defmodule ColouredFlow.Definition.PresentationTest do
         """
       )
     end
+
+    test "collapses multi-line composite types into single-line %% comments" do
+      # `Macro.to_string` returns multi-line output for map descrs. Mermaid's
+      # `%%` only comments a single line, so without collapsing, the parser
+      # bails with "Expecting NEWLINE/EOF, got NODE_STRING" on the trailing
+      # lines that escape the comment.
+      cpnet = %ColouredPetriNet{
+        colour_sets: [
+          %ColourSet{
+            name: :user,
+            type: {:map, %{name: {:binary, []}, age: {:integer, []}}}
+          }
+        ],
+        places: [%Place{name: "p", colour_set: :user}],
+        transitions: [],
+        arcs: [],
+        variables: [],
+        constants: [],
+        functions: []
+      }
+
+      mermaid = Presentation.to_mermaid(cpnet)
+      [colset_line] = Regex.run(~r/%% colset .+/, mermaid)
+
+      assert colset_line =~ "%% colset user() ::"
+      refute String.contains?(colset_line, "\n")
+    end
   end
 
   defp assert_mermaid(cpnet, expected) do