feat(halacha): equivalent-halacha (parallel-authority) links across precedents

Cross-precedent recurrence of a principle is real but is NOT citation
corroboration (X11) — the 5 candidate pairs have ZERO citations between their
precedents. Recording them in halacha_citation_corroboration would fabricate
citation data and inflate corroboration_count. This adds a proper, separate
halacha-level link for parallel authority.

Schema (V28): equivalent_halachot — symmetric (halacha_a < halacha_b, CHECK +
UNIQUE), non-citation, cross-precedent-only. ON DELETE CASCADE.

db.py:
- link_equivalent_halachot (idempotent; rejects same-id and SAME-precedent pairs
  — parallel authority is cross-precedent by definition), unlink, and
  list_equivalent_for_halacha.
- list_halachot gains include_equivalents → _annotate_equivalents attaches an
  `equivalents` list (both directions) per row.

API: include_equivalents on GET /api/halachot; GET/POST/DELETE
/api/halachot/{id}/equivalents for the chair to view/link/unlink manually.

scripts/halacha_batch_reconcile.py: --link records found cross-precedent pairs
as equivalent_halachot (non-destructive, idempotent).

web-ui: Halacha.equivalents type; the clean review queue fetches
include_equivalents; the review card shows a gold "עיקרון מקביל ב-N" badge + an
expandable list (case + rule + similarity) labeled "אסמכתה מקבילה — לא ציטוט".

Populated the 5 reviewed pairs (chair decision: keep all + link as parallel
authority). Verified: 5 rows; the 1023-20 hub annotates 3 of its halachot with
equivalents; tsc --noEmit exits 0.

Invariants: G1 (model recurrence at source in its own table, not by abusing the
citator); G2 (no parallel path — extends list_halachot); citator integrity
preserved (corroboration stays citation-only).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/halacha_batch_reconcile.py

@@ -91,7 +91,22 @@ async def main(args: argparse.Namespace) -> int:
             w = csv.DictWriter(f, fieldnames=list(pairs[0].keys()))
             w.writeheader()
             w.writerows(pairs)
-        print(f"\nreport: {out}  (review-only — nothing changed)", flush=True)
+        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)
     return 0
 
 
@@ -102,5 +117,7 @@ if __name__ == "__main__":
                     help="min cosine for a cross-precedent candidate (default 0.95)")
     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)")
     args = ap.parse_args()
     sys.exit(asyncio.run(main(args)))