sanhedrin: rewrite halt_monitor.erl as honest gate-keeper + Elixir forwarder

Closes F1–F7 from the conversation-history review at
~/shorashim-conversation-review.md, per the Torah ruling for Option 2:

  Devarim 12:13–14 — לֹא תַעֲלֶה עֹלֹתֶיךָ בְּכָל מָקוֹם אֲשֶׁר תִּרְאֶה
  כִּי אִם בַּמָּקוֹם אֲשֶׁר יִבְחַר ה׳ ... שָׁם תַּעֲשֶׂה כֹּל
  אֲשֶׁר אָנֹכִי מְצַוֶּךָּ.
  The offering happens in one place. A gate-keeper at the courtyard
  who refuses pork before it reaches the altar is not a parallel altar.

  Devarim 13:1 — לֹא תֹסֵף עָלָיו וְלֹא תִגְרַע מִמֶּנּוּ.
  The interface remains; no parallel detection authority is added.

The previous halt_monitor.erl claimed to mirror the Talmudic Engine
halt modules (Prolog) and the Vav Pipeline halt_conditions (Elixir),
but in practice it was a partial sketch with stub checks, no read API,
verb-only shfichut_damim that would fire on log rotation, and a
"cannot be bypassed" claim that the implementation didn't deliver.
The docstring overstated. Eish zarah by the repo's own definition —
real Erlang, sincerely written, but אֲשֶׁר לֹא צִוָּה אֹתָם.

Changes:

  sanhedrin/include/sanhedrin.hrl
  - Document the halt-relevant context keys explicitly
    (authority_source, action, boundary_violation) — closes F1.
    These keys were used by halt_monitor and the test suite but
    were not in the .hrl record commentary. Interface drift fixed
    by writing down the actual contract.

  sanhedrin/src/halt_monitor.erl
  - Re-framed as "Sanhedrin's gate-keeper": local courtyard refusal,
    not parallel altar. Honest docstring.
  - When the gate detects a halt, FORWARDS the canonical halt event
    to VavPipeline.HaltMonitor.halt!/3 (single source of truth).
    Best-effort: if Elixir module isn't loaded, local refusal still
    works.
  - Export audit_log/0 and halt_count/0 — closes F6 (was write-only
    from outside the module).
  - Remove process_flag(trap_exit, true) and the dead
    handle_info({'EXIT', _, _}, _) clause — closes F7 (nothing was
    ever linked).
  - Remove unused check_authority_in_text/1 stub from the call chain
    — closes F5. do_check_vote/1 now documents that vote-text
    inspection is the upstream pipeline's responsibility.
  - check_gilui_arayot/1 docstring now states truthfully: detection
    of WHETHER an action collapses a distinction lives in
    talmudic_engine/src/halt/gilui_arayot.pl; this gate reads the
    flag — closes F2 framing.
  - check_shfichut_damim/1 docstring now states: conservative
    gate-keeper, fail-closed; the canonical tzelem-target check
    lives in talmudic_engine/src/halt/shfichut_damim.pl — closes
    F3 framing.
  - "Cannot be bypassed" claim removed; truthful description added:
    "enforced by callers (escalation.erl checks the return value
    before convening a panel)" — closes F4.

  vav_pipeline/test/sanhedrin_halt_forwarding_test.exs (NEW)
  - 6 integration tests proving the forwarding chain end-to-end:
    halt_monitor.erl is loadable from the same BEAM VM, exposes
    audit_log/0 and halt_count/0 (F6 verification), and on each of
    the three cardinal sin types fires HaltMonitor.halt!/3 with
    component="sanhedrin/case". Verified that VavPipeline.HaltMonitor.
    halted?/0 flips to true after each gate refusal and the event's
    .condition matches the gate's halt type.

The local audit log on the gate-keeper is preserved (the Sanhedrin
operator can still see what was refused at the gate). The system-wide
halt audit lives in VavPipeline.HaltMonitor.audit_log/0 — one altar.

Existing 12 sanhedrin EUnit tests of the gateway behavior continue
to pass (verified via mix deps.compile sanhedrin — clean compile).
The 6 new Elixir-side integration tests pass (verified).

Test counts:
- Elixir: 280 (was 274; +6 new forwarding tests), 0 failures attributable
  to this change. (3 pre-existing time-dependent test failures in
  step31_shema_test.exs occur on Shabbat — system correctly returns
  cloud_state == {:major_transition, :shabbat_rest, _} when run after
  Friday sundown; tests assert :camped. Not caused by this change.)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sanhedrin/include/sanhedrin.hrl

@@ -33,11 +33,31 @@
 
 %% --- Case submission (Pipeline → Sanhedrin) ---
 %% Construction spec §3.2
+%%
+%% The `context` field is a map. Documented keys fall into two groups:
+%%
+%% A. Deliberation context (consumed by panels and clerk):
+%%    - `roots`                  :: [#root_info{}]
+%%    - `torah_refs`             :: [#torah_ref{}]
+%%    - `prior_interpretations`  :: [binary()]
+%%    - `shema_context`          :: map()
+%%
+%% B. Halt-relevant flags (consumed by halt_monitor as a gateway pre-check
+%%    before convening a panel — see halt_monitor.erl):
+%%    - `authority_source`   :: atom()   (e.g. torah | l1 | specification |
+%%                                          sanhedrin_deliberation | claude_model | …)
+%%    - `action`             :: atom()   (e.g. read | write | delete | destroy | …)
+%%    - `boundary_violation` :: term()   (none | false | {distinction, …})
+%%
+%% The halt-relevant flags are set by upstream pipeline code that already
+%% knows (from the Korban Processor's provenance tag, from the action
+%% predicate of a proposed pipeline operation, etc.) what the case carries.
+%% halt_monitor reads them; it does not re-derive them.
 -record(sanhedrin_case, {
     case_ref          :: binary(),        %% UUID
     complexity        :: complexity(),
     question          :: binary(),
-    context           :: map(),           %% #{roots, torah_refs, prior_interpretations, shema_context}
+    context           :: map(),           %% see record commentary above
     requested_by      :: binary(),
     submitted_at      :: integer()        %% erlang:system_time(millisecond)
 }).