feat(halachot): Phase 6 — deprecate equivalent_halachot writes post-V41

- halacha_batch_reconcile.py --link now exits with error (V41 freezes
  equivalent_halachot; equivalences live in canonical_id instead)
- link_equivalent_halachot emits DeprecationWarning (callers ≥ Python 3.2)
- SCRIPTS.md already marks --link as deprecated; no further doc change needed

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

mcp-server/src/legal_mcp/services/db.py

@@ -5936,11 +5936,21 @@ def _equiv_order(a: UUID, b: UUID) -> tuple[UUID, UUID]:
 async def link_equivalent_halachot(
     a: UUID, b: UUID, *, cosine: float = 0.0, note: str = "", created_by: str = "",
 ) -> bool:
-    """Record that two halachot (different precedents) state the same principle.
+    """[DEPRECATED since V41] Record a parallel-authority link in equivalent_halachot.
+
+    The canonical_halachot model (V41) supersedes this table — cross-precedent
+    equivalence is now expressed via halachot.canonical_id. This function is kept
+    for historical callers only; no new code should call it. Use
+    ``create_canonical_halacha`` + ``nearest_canonical_halacha`` instead.
 
     Idempotent (symmetric UNIQUE). Returns False and does nothing if a == b or
-    the two belong to the SAME precedent (parallel authority is cross-precedent
-    by definition; within-precedent sameness is the dedup/cluster concern)."""
+    the two belong to the SAME precedent."""
+    import warnings
+    warnings.warn(
+        "link_equivalent_halachot is deprecated since V41 (canonical_halachot). "
+        "Use create_canonical_halacha / nearest_canonical_halacha instead.",
+        DeprecationWarning, stacklevel=2,
+    )
     if a == b:
         return False
     pool = await get_pool()

scripts/halacha_batch_reconcile.py

@@ -93,20 +93,20 @@ async def main(args: argparse.Namespace) -> int:
             w.writerows(pairs)
         print(f"\nreport: {out}", flush=True)
 
-    if args.link and pairs:
-        # #84.2 — record each pair as parallel authority (equivalent_halachot).
-        # Non-destructive: links only, never merges/deletes. Idempotent.
-        linked = 0
-        for p in pairs:
-            if await db.link_equivalent_halachot(
-                p["id_a"], p["id_b"], cosine=p["cosine"],
-                note="cross-precedent parallel authority (halacha_batch_reconcile)",
-                created_by="batch_reconcile",
-            ):
-                linked += 1
-        print(f"linked {linked}/{len(pairs)} pairs as equivalent_halachot", flush=True)
-    elif pairs:
-        print("(review-only — pass --link to record them as equivalent_halachot)", flush=True)
+    if args.link:
+        # V41 (canonical_halachot): equivalent_halachot is FROZEN — no new links.
+        # Use backfill_canonical_halachot.py --apply instead.
+        print(
+            "\nERROR: --link is deprecated since V41 (canonical_halachot model).\n"
+            "  equivalent_halachot is read-only and frozen post-backfill.\n"
+            "  Cross-precedent dedup is now handled by the canonical model:\n"
+            "    mcp-server/.venv/bin/python scripts/backfill_canonical_halachot.py --apply\n"
+            "  Exiting without writing any links.",
+            flush=True,
+        )
+        return 1
+    if pairs:
+        print("(review-only — pair report saved above)", flush=True)
     return 0
 
 
@@ -118,6 +118,6 @@ if __name__ == "__main__":
     ap.add_argument("--include-pending", action="store_true",
                     help="also scan pending_review halachot (default: approved/published only)")
     ap.add_argument("--link", action="store_true",
-                    help="record found pairs as equivalent_halachot (parallel authority, #84.2)")
+                    help="[DEPRECATED since V41] refused at runtime — use backfill_canonical_halachot.py")
     args = ap.parse_args()
     sys.exit(asyncio.run(main(args)))