tablet 55: the row that was a label — the Sanhedrin's example request crashed its own gate

Verified live 2026-10-19: Tamid's own example for POST /chatzer/sanhedrin
(a case with `sides`) answered 500. The router passed the sides LIST as
the case context; halt_monitor:check_avodah_zarah/1 reads a map, maps:get
raised, and the halt monitor and escalation gen_servers died with the
caller's input (supervisor restarted them; health stayed 8/8). The router
then matched {:ok, decision} on the error and made a 500 of its own.

- sanhedrin/src/halt_monitor.erl: do_check_case refuses a non-map
  context as {halt, malformed_case, _} and stays standing. EUnit 49/0
  with the new halt_malformed_context_test.
- router.ex process_sanhedrin: sides validated at the kiyor (422 on a bad
  shape), carried as context %{sides: sides}; a Sanhedrin refusal answers
  422 SANHEDRIN_HALTED, a failure 503 SANHEDRIN_UNAVAILABLE. Two new
  router tests, one asserting the gate processes survive the example.
  Elixir 624/0.
- specs/broken_tablets/README.md: tablet 55, including what is NOT fixed
  — a panel of one accepting on zero references under a grounded-
  sounding sentence, the ignored complexity hint, no panel manna spent,
  no L3 record. The row in Tamid is still larger than the thing behind it.

Doorpost pin unchanged (no @spec_files touched; scripts/doorpost_check.py
passes).

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

vav_pipeline/test/bigdei_kodesh_test.exs

@@ -317,6 +317,43 @@ defmodule VavPipeline.BigdeiKodeshTest do
       assert body["deliberation"]["outcome"] in ["accepted", "rejected", "teiku"]
       assert body["note"] =~ "not a binding ruling"
     end
+
+    # Tablet 55: the Tamid's own example — a case WITH sides — returned
+    # 500 and took the halt monitor and escalation down with it.
+    test "POST /chatzer/sanhedrin with sides (the Tamid's example) deliberates" do
+      conn =
+        conn(:post, "/chatzer/sanhedrin", Jason.encode!(%{
+          case: "A borrower repaid before one witness; the lender denies receipt. Who bears the burden?",
+          sides: [
+            %{position: "the borrower is believed", evidence: ["the money was handed over before a witness"]},
+            %{position: "the lender is believed", evidence: ["one witness does not establish payment"]}
+          ],
+          complexity_hint: "monetary"
+        }))
+        |> put_req_header("content-type", "application/json")
+        |> put_req_header("authorization", "Bearer chatzer-test-token")
+        |> Router.call(@opts)
+
+      assert conn.status == 200
+      body = Jason.decode!(conn.resp_body)
+      assert body["deliberation"]["outcome"] in ["accepted", "rejected", "teiku"]
+      # and the gate is still standing afterwards
+      assert Process.whereis(:halt_monitor) != nil
+      assert Process.whereis(:escalation) != nil
+    end
+
+    test "POST /chatzer/sanhedrin with malformed sides returns 422, not 500" do
+      for bad <- ["not a list", [%{"no_position" => 1}], [%{"position" => "p", "evidence" => "not a list"}]] do
+        conn =
+          conn(:post, "/chatzer/sanhedrin", Jason.encode!(%{case: "x", sides: bad}))
+          |> put_req_header("content-type", "application/json")
+          |> put_req_header("authorization", "Bearer chatzer-test-token")
+          |> Router.call(@opts)
+
+        assert conn.status == 422, "expected 422 for sides=#{inspect(bad)}, got #{conn.status}"
+        assert Jason.decode!(conn.resp_body)["error"]["code"] == "KIYOR_VALIDATION_FAILED"
+      end
+    end
   end
 
   # ============================================================