diff --git a/blockchain/__init__.py b/blockchain/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/blockchain/seal.py b/blockchain/seal.py
new file mode 100644
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--- /dev/null
+++ b/blockchain/seal.py
@@ -0,0 +1,366 @@
+#!/usr/bin/env python3
+"""
+seal.py — Polygon PoS sealing module for PGŽ Sport audit log
+Author: Damir Radulić (damir@rinet.one) / dradulic@outlook.com
+Date: 2026-05-04
+Version: 1.0.0
+
+Seals critical audit events to Polygon PoS (chain 137) using the wallet
+0xD874345dcB17baBDfbFac9bD7838AdE0D4a5d368.
+
+Two operating modes:
+
+1. LIVE  — environment provides POLYGON_PRIVKEY (and web3 is installed).
+           A 0-MATIC self-transaction is sent with the sha256 data hash encoded
+           in the `data` field. Returns the real 0x… 64-char tx hash.
+
+2. PENDING — no key configured. The seal record is queued in
+             pgz_sport.polygon_seals with status='pending' and a deterministic
+             pseudo-tx-hash (the seal_id, prefixed with 'pending:'). A later
+             batch job (or operator) can flush the queue once a key is loaded.
+
+Public surface
+--------------
+seal_to_polygon(data_hash, ref_id, action, **kw) -> dict
+    Returns:  { seal_id, tx_hash, status, polygonscan_url, ... }
+
+verify_seal(seal_id) -> dict
+    Read-back utility. Cross-checks the on-chain receipt (if web3 is wired up)
+    and returns the canonical row from polygon_seals.
+
+list_seals(action=None, ref_type=None, ref_id=None, limit=50) -> list[dict]
+    Lightweight reader for the audit-seal UI.
+
+The module is import-safe even on hosts without web3 installed; the LIVE branch
+just becomes a no-op.
+"""
+from __future__ import annotations
+
+import os
+import json
+import hashlib
+import time
+from datetime import datetime, timezone
+from typing import Optional, Any
+
+import psycopg2
+import psycopg2.extras
+
+# ─── Optional web3 dependency ────────────────────────────────────────────
+try:
+    from web3 import Web3
+    from eth_account import Account
+    HAS_WEB3 = True
+except Exception:
+    HAS_WEB3 = False
+
+# ─── Configuration (env-driven) ──────────────────────────────────────────
+POLYGON_RPC      = os.environ.get("POLYGON_RPC", "https://polygon-rpc.com")
+POLYGON_CHAIN_ID = int(os.environ.get("POLYGON_CHAIN_ID", "137"))
+POLYGON_WALLET   = os.environ.get(
+    "POLYGON_WALLET", "0xD874345dcB17baBDfbFac9bD7838AdE0D4a5d368"
+).strip()
+POLYGON_PRIVKEY  = os.environ.get("POLYGON_PRIVKEY", "").strip()
+POLYGONSCAN_BASE = os.environ.get("POLYGONSCAN_BASE", "https://polygonscan.com")
+
+DB = dict(
+    host=os.environ.get("PG_HOST", "10.10.0.2"),
+    port=int(os.environ.get("PG_PORT", "6432")),
+    dbname=os.environ.get("PG_DB", "rinet_v3"),
+    user=os.environ.get("PG_USER", "rinet"),
+    password=os.environ.get("PG_PASS", "R1net2026!SecureDB#v7"),
+)
+
+# ─── helpers ─────────────────────────────────────────────────────────────
+
+
+def _db():
+    c = psycopg2.connect(**DB)
+    c.autocommit = True
+    return c
+
+
+def _sha256(*parts: Any) -> str:
+    h = hashlib.sha256()
+    for p in parts:
+        if p is None:
+            continue
+        if isinstance(p, (dict, list)):
+            p = json.dumps(p, sort_keys=True, ensure_ascii=False, default=str)
+        h.update(str(p).encode("utf-8", errors="replace"))
+        h.update(b"\x00")
+    return h.hexdigest()
+
+
+def hash_payload(payload: Any) -> str:
+    """Public helper — stable sha256 of a payload, JSON-canonicalised."""
+    if isinstance(payload, (dict, list)):
+        payload = json.dumps(payload, sort_keys=True, ensure_ascii=False, default=str)
+    return hashlib.sha256(str(payload).encode("utf-8", errors="replace")).hexdigest()
+
+
+def polygonscan_url(tx_hash: str) -> Optional[str]:
+    if not tx_hash or tx_hash.startswith("pending:"):
+        return None
+    if not tx_hash.startswith("0x"):
+        tx_hash = "0x" + tx_hash
+    return f"{POLYGONSCAN_BASE}/tx/{tx_hash}"
+
+
+# ─── live broadcast path ─────────────────────────────────────────────────
+
+
+def _broadcast_live(data_hash: str, action: str, ref_id: str) -> dict:
+    """Send a 0-MATIC self-tx encoding `data_hash` in the data field.
+
+    Returns dict with tx_hash, block_number (if mined within wait window),
+    and status. Raises on RPC errors so the caller can fall back.
+    """
+    if not HAS_WEB3:
+        raise RuntimeError("web3 not installed")
+    if not POLYGON_PRIVKEY:
+        raise RuntimeError("POLYGON_PRIVKEY missing")
+
+    w3 = Web3(Web3.HTTPProvider(POLYGON_RPC, request_kwargs={"timeout": 15}))
+    acct = Account.from_key(POLYGON_PRIVKEY)
+
+    if acct.address.lower() != POLYGON_WALLET.lower():
+        raise RuntimeError(
+            f"key/address mismatch: key={acct.address} wallet={POLYGON_WALLET}"
+        )
+
+    nonce = w3.eth.get_transaction_count(acct.address)
+    gas_price = w3.eth.gas_price
+
+    # Encode "PGZ|action|ref_id|data_hash" into the data field as utf-8 hex.
+    memo = f"PGZ|{action}|{ref_id}|0x{data_hash}".encode("utf-8")
+    tx = {
+        "to": acct.address,
+        "value": 0,
+        "data": "0x" + memo.hex(),
+        "nonce": nonce,
+        "chainId": POLYGON_CHAIN_ID,
+        "gas": 60000,
+        "gasPrice": gas_price,
+    }
+    signed = acct.sign_transaction(tx)
+    tx_hash = w3.eth.send_raw_transaction(signed.rawTransaction).hex()
+
+    block_number = None
+    try:
+        receipt = w3.eth.wait_for_transaction_receipt(tx_hash, timeout=30)
+        block_number = int(receipt.blockNumber)
+        status = "confirmed" if receipt.status == 1 else "failed"
+    except Exception:
+        status = "broadcast"
+
+    return {"tx_hash": tx_hash, "block_number": block_number, "status": status}
+
+
+# ─── public API ──────────────────────────────────────────────────────────
+
+
+def seal_to_polygon(
+    data_hash: str,
+    ref_id: str,
+    action: str,
+    *,
+    ref_type: Optional[str] = None,
+    payload: Optional[Any] = None,
+    user_id: Optional[int] = None,
+    user_email: Optional[str] = None,
+) -> dict:
+    """Seal a sha256 hash to Polygon PoS.
+
+    Always persists a row in pgz_sport.polygon_seals. If LIVE mode succeeds,
+    the row carries the real tx_hash; otherwise it is left in 'pending' state
+    so a worker can flush the queue later.
+
+    Parameters
+    ----------
+    data_hash : str
+        sha256 hex digest of the payload being sealed.
+    ref_id : str
+        opaque reference (e.g. "klub:42", "sufinanciranje:2026-001").
+    action : str
+        canonical action name (e.g. "sufinanciranje.approved").
+    """
+    if not data_hash:
+        raise ValueError("data_hash required")
+    data_hash = data_hash.lower().lstrip("0x")
+    if len(data_hash) != 64 or not all(c in "0123456789abcdef" for c in data_hash):
+        raise ValueError("data_hash must be 64-char sha256 hex")
+
+    nonce = f"{int(time.time() * 1000):x}"
+    seal_id = _sha256(action, ref_id, data_hash, nonce)
+
+    row = {
+        "seal_id": seal_id,
+        "action": action[:80],
+        "ref_type": (ref_type or "")[:50] or None,
+        "ref_id": str(ref_id)[:80] if ref_id is not None else None,
+        "data_hash": data_hash,
+        "payload": json.dumps(payload, default=str) if payload is not None else None,
+        "wallet": POLYGON_WALLET,
+        "chain_id": POLYGON_CHAIN_ID,
+        "user_id": user_id,
+        "user_email": user_email,
+    }
+
+    tx_hash: Optional[str] = None
+    block_number: Optional[int] = None
+    error: Optional[str] = None
+    status = "pending"
+
+    if HAS_WEB3 and POLYGON_PRIVKEY:
+        try:
+            r = _broadcast_live(data_hash, action, str(ref_id))
+            tx_hash = r["tx_hash"]
+            block_number = r.get("block_number")
+            status = r.get("status", "broadcast")
+        except Exception as e:
+            error = f"{type(e).__name__}: {e}"[:500]
+            status = "pending"
+            tx_hash = None
+    else:
+        # No live key: deterministic "pending" reference.
+        tx_hash = "pending:" + seal_id[:32]
+        if not HAS_WEB3:
+            error = "web3 not installed"
+        elif not POLYGON_PRIVKEY:
+            error = "POLYGON_PRIVKEY not set"
+
+    sealed_at = datetime.now(timezone.utc) if status in ("broadcast", "confirmed") else None
+
+    with _db() as c, c.cursor() as cur:
+        cur.execute(
+            """
+            INSERT INTO pgz_sport.polygon_seals
+              (seal_id, action, ref_type, ref_id, data_hash, payload, tx_hash,
+               chain_id, wallet, status, block_number, error,
+               user_id, user_email, sealed_at)
+            VALUES (%(seal_id)s, %(action)s, %(ref_type)s, %(ref_id)s, %(data_hash)s,
+                    %(payload)s::jsonb, %(tx_hash)s, %(chain_id)s, %(wallet)s,
+                    %(status)s, %(block_number)s, %(error)s,
+                    %(user_id)s, %(user_email)s, %(sealed_at)s)
+            ON CONFLICT (seal_id) DO UPDATE
+              SET tx_hash      = EXCLUDED.tx_hash,
+                  status       = EXCLUDED.status,
+                  block_number = EXCLUDED.block_number,
+                  error        = EXCLUDED.error,
+                  sealed_at    = EXCLUDED.sealed_at
+            RETURNING id, created_at
+            """,
+            {
+                **row,
+                "tx_hash": tx_hash,
+                "status": status,
+                "block_number": block_number,
+                "error": error,
+                "sealed_at": sealed_at,
+            },
+        )
+        rid, created_at = cur.fetchone()
+
+    return {
+        "id": rid,
+        "seal_id": seal_id,
+        "action": action,
+        "ref_type": ref_type,
+        "ref_id": ref_id,
+        "data_hash": data_hash,
+        "tx_hash": tx_hash,
+        "status": status,
+        "block_number": block_number,
+        "wallet": POLYGON_WALLET,
+        "chain_id": POLYGON_CHAIN_ID,
+        "polygonscan_url": polygonscan_url(tx_hash),
+        "error": error,
+        "created_at": created_at.isoformat() if created_at else None,
+        "live": HAS_WEB3 and bool(POLYGON_PRIVKEY),
+    }
+
+
+def verify_seal(seal_id: str) -> Optional[dict]:
+    with _db() as c, c.cursor(cursor_factory=psycopg2.extras.RealDictCursor) as cur:
+        cur.execute(
+            """SELECT id, seal_id, action, ref_type, ref_id, data_hash, tx_hash,
+                      chain_id, wallet, status, block_number, error,
+                      user_id, user_email, created_at, sealed_at, payload
+               FROM pgz_sport.polygon_seals WHERE seal_id=%s""",
+            (seal_id,),
+        )
+        row = cur.fetchone()
+    if not row:
+        return None
+    row = dict(row)
+    row["polygonscan_url"] = polygonscan_url(row.get("tx_hash"))
+    if row.get("created_at"):
+        row["created_at"] = row["created_at"].isoformat()
+    if row.get("sealed_at"):
+        row["sealed_at"] = row["sealed_at"].isoformat()
+
+    if HAS_WEB3 and row.get("tx_hash") and not str(row["tx_hash"]).startswith("pending:"):
+        try:
+            w3 = Web3(Web3.HTTPProvider(POLYGON_RPC, request_kwargs={"timeout": 8}))
+            r = w3.eth.get_transaction_receipt(row["tx_hash"])
+            row["onchain"] = {
+                "block_number": int(r.blockNumber),
+                "status": int(r.status),
+                "from": r["from"],
+                "to": r["to"],
+            }
+        except Exception as e:
+            row["onchain"] = {"error": str(e)[:200]}
+    return row
+
+
+def list_seals(
+    action: Optional[str] = None,
+    ref_type: Optional[str] = None,
+    ref_id: Optional[str] = None,
+    limit: int = 50,
+) -> list[dict]:
+    where, params = [], []
+    if action:
+        where.append("action = %s")
+        params.append(action)
+    if ref_type:
+        where.append("ref_type = %s")
+        params.append(ref_type)
+    if ref_id is not None:
+        where.append("ref_id = %s")
+        params.append(str(ref_id))
+    sql = (
+        "SELECT id, seal_id, action, ref_type, ref_id, data_hash, tx_hash, "
+        "       chain_id, wallet, status, block_number, error, "
+        "       user_id, user_email, created_at, sealed_at "
+        "FROM pgz_sport.polygon_seals "
+        + ("WHERE " + " AND ".join(where) + " " if where else "")
+        + "ORDER BY id DESC LIMIT %s"
+    )
+    params.append(min(int(limit or 50), 500))
+    with _db() as c, c.cursor(cursor_factory=psycopg2.extras.RealDictCursor) as cur:
+        cur.execute(sql, params)
+        rows = [dict(r) for r in cur.fetchall()]
+    for r in rows:
+        r["polygonscan_url"] = polygonscan_url(r.get("tx_hash"))
+        if r.get("created_at"):
+            r["created_at"] = r["created_at"].isoformat()
+        if r.get("sealed_at"):
+            r["sealed_at"] = r["sealed_at"].isoformat()
+    return rows
+
+
+# ─── self-test ───────────────────────────────────────────────────────────
+if __name__ == "__main__":
+    payload = {"demo": True, "ts": int(time.time()), "msg": "PGŽ seal self-test"}
+    h = hash_payload(payload)
+    res = seal_to_polygon(
+        h,
+        ref_id="selftest:1",
+        action="selftest.run",
+        ref_type="selftest",
+        payload=payload,
+    )
+    print(json.dumps(res, indent=2, default=str, ensure_ascii=False))