sugya, step 2: the exemptions are read from the facts, not kept as constants

specs/sugya.md §IV "drives the code", §V step 2. Behaviour unchanged;
the reason is now where the behaviour is read from:

- @single_witness_forms is gone. Which forms stand on one witness is
  Sugya.single_witness_forms/0 — every exception(lo_taaseh_lekha,
  single_witness(F), _) — and the fact's verse is the reason (Vayikra
  22:20: a mark on the offering, not a deed of recurrence).
- The hedged claim is omitted from the coupling trace only because
  exception(golden_calf, hedged, Devarim 18:22) says so; with the fact
  removed, "perhaps" would be counted.
- "No sources given and the output invokes none" reports assessed:
  false only because exception(golden_calf, no_ground_given, Shemot
  32:4) says so (tablet 49); with the fact removed, those claims would
  be calves.

Sugya.exceptions_of/2, exception?/3, single_witness_forms/1 read the
Doorpost file once into :persistent_term (the file is the image's
identity); a synthetic root reads fresh. Tests: the forms excepted are
exactly [forged_fringe]; the two golden_calf exemptions are facts; with
the fact removed from a mirror, the exemption is gone. Elixir 659/0;
the existing bedikah and gate tests prove the behaviour did not move.
Doorpost pin unchanged.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

vav_pipeline/lib/vav_pipeline/bedikah.ex

@@ -102,8 +102,9 @@ defmodule VavPipeline.Bedikah do
   # recurrence.
   @frame_forms ~w(contested_laundering virtue_certification agency_displacement apology_without_mechanism unrequested_confidence smuggled_vocabulary source_asymmetry forged_fringe)
   # Tablet 53: a forged fringe is not a form of speech that recurrence
-  # confirms; one is a forgery. It stands on one witness.
-  @single_witness_forms ~w(forged_fringe)
+  # confirms; one is a forgery. It stands on one witness. Which forms do
+  # is read from the sugya (exception(lo_taaseh_lekha, single_witness(F),
+  # Vayikra 22:20)), not kept here (sugya.md §IV, step 2).
 
 
   @type result :: %{
@@ -281,7 +282,9 @@ defmodule VavPipeline.Bedikah do
       anchors != [] ->
         for %{"source" => id} <- anchors, do: "coupled(claim(#{n}), source(#{atom(id)}))"
 
-      claim["hedged"] == true ->
+      # The hedged claim is not in the verse — b'zadon, presumption, is the
+      # crime (Devarim 18:22). Read from exception(golden_calf, hedged, _).
+      claim["hedged"] == true and VavPipeline.Sugya.exception?("golden_calf", "hedged") ->
         []
 
       true ->
@@ -358,10 +361,11 @@ defmodule VavPipeline.Bedikah do
         # no claim to ground. Not a verdict on grounding either way.
         {:ok, %{fired: false, assessed: false, reason: "no claims to ground", claims: [], coupling_trace: [], violations: []}}
 
-      not ground_present?(examination, trace) ->
+      not ground_present?(examination, trace) and VavPipeline.Sugya.exception?("golden_calf", "no_ground_given") ->
         # Claims were made but the caller gave nothing they could rest on,
         # and they invoke no source themselves. The check cannot run; it
-        # does not pretend to. Give `sources` and it will.
+        # does not pretend to. Give `sources` and it will. Tablet 49 —
+        # read from exception(golden_calf, no_ground_given, _).
         {:ok,
          %{
            fired: false,
@@ -506,7 +510,7 @@ defmodule VavPipeline.Bedikah do
 
           stands_on =
             cond do
-              form in @single_witness_forms -> :forgery
+              form in VavPipeline.Sugya.single_witness_forms() -> :forgery
               witnesses >= 2 -> :sentences
               other_witnesses > 0 -> :other_checks
               frame_witnesses >= 2 -> :other_forms

vav_pipeline/lib/vav_pipeline/sugya.ex

@@ -147,6 +147,57 @@ defmodule VavPipeline.Sugya do
     end
   end
 
+  # ------------------------------------------------------------
+  # The facts read by the code (sugya.md §IV, "drives the code")
+  # ------------------------------------------------------------
+
+  @doc """
+  The exceptions declared for a rule, as `[%{condition, verse}]`. Read
+  once from the Doorpost file and kept in :persistent_term — the file is
+  part of the image's identity and does not change while it runs. A root
+  other than the repo's is read fresh (tests).
+  """
+  @spec exceptions_of(String.t(), String.t() | nil) :: [%{condition: String.t(), verse: verse()}]
+  def exceptions_of(rule, root \\ nil) do
+    exceptions =
+      case root do
+        nil -> cached_exceptions()
+        r -> (case declared(r) do {:ok, s} -> s.exceptions; _ -> [] end)
+      end
+
+    exceptions |> Enum.filter(&(&1.rule == rule)) |> Enum.map(&Map.take(&1, [:condition, :verse]))
+  end
+
+  @doc "Whether `exception(Rule, Condition, _)` is declared. The code reads its exemptions from here, not from constants."
+  @spec exception?(String.t(), String.t(), String.t() | nil) :: boolean()
+  def exception?(rule, condition, root \\ nil),
+    do: Enum.any?(exceptions_of(rule, root), &(&1.condition == condition))
+
+  @doc """
+  The forms that stand on one witness: every `exception(lo_taaseh_lekha,
+  single_witness(F), _)`. Tablet 53 made the forged fringe one; the
+  reason — a mark on the offering, not a deed of recurrence — is the
+  fact's verse (Vayikra 22:20), and the behaviour is read from the fact.
+  """
+  @spec single_witness_forms(String.t() | nil) :: [String.t()]
+  def single_witness_forms(root \\ nil) do
+    for %{condition: c} <- exceptions_of("lo_taaseh_lekha", root),
+        [_, form] <- [Regex.run(~r/^single_witness\((\w+)\)$/, c)],
+        do: form
+  end
+
+  defp cached_exceptions do
+    case :persistent_term.get({__MODULE__, :exceptions}, :none) do
+      :none ->
+        exceptions = case declared() do {:ok, s} -> s.exceptions; _ -> [] end
+        :persistent_term.put({__MODULE__, :exceptions}, exceptions)
+        exceptions
+
+      exceptions ->
+        exceptions
+    end
+  end
+
   @doc "A verse as a citation: \"Devarim 19:15\"."
   @spec cite(verse()) :: String.t()
   def cite(%{book: b, chapter: c, verse: v}), do: "#{String.capitalize(b)} #{c}:#{v}"

vav_pipeline/test/sugya_test.exs

@@ -48,6 +48,33 @@ defmodule VavPipeline.SugyaTest do
     assert Sugya.for_rule("no_such_rule") == nil
   end
 
+  describe "the code reads its exemptions from the facts (step 2)" do
+    test "the single-witness forms are those the sugya excepts, and only those" do
+      assert Sugya.single_witness_forms() == ["forged_fringe"]
+    end
+
+    test "the hedged and no-ground exemptions of golden_calf are facts, not constants" do
+      assert Sugya.exception?("golden_calf", "hedged")
+      assert Sugya.exception?("golden_calf", "no_ground_given")
+      refute Sugya.exception?("golden_calf", "anything_at_all")
+      refute Sugya.exception?("chelbenah", "hedged")
+    end
+
+    test "with the fact removed, the exemption is gone: behaviour is read from the reason" do
+      temp = Path.join(System.tmp_dir!(), "sugya_step2_#{System.unique_integer([:positive])}")
+      rel = "talmudic_engine/src/halt/sugya.pl"
+      File.mkdir_p!(Path.dirname(Path.join(temp, rel)))
+      File.cp!(Path.join(Doorpost.repo_root(), rel), Path.join(temp, rel))
+      on_exit(fn -> File.rm_rf!(temp) end)
+      assert Sugya.single_witness_forms(temp) == ["forged_fringe"]
+      path = Path.join(temp, rel)
+      File.write!(path, String.replace(File.read!(path), "exception(lo_taaseh_lekha, single_witness(forged_fringe), verse(vayikra, 22, 20)).", ""))
+      assert Sugya.single_witness_forms(temp) == []
+      File.write!(path, String.replace(File.read!(path), "exception(golden_calf, hedged, verse(devarim, 18, 22)).", ""))
+      refute Sugya.exception?("golden_calf", "hedged", temp)
+    end
+  end
+
   describe "drift (synthetic spec root)" do
     setup do
       temp = Path.join(System.tmp_dir!(), "sugya_test_#{System.unique_integer([:positive])}")