feat(notify): alert the operator over Nostr when a customer is owed cash

cash_owed / partial_pending now sends a NIP-17 gift-wrapped DM (kind 14
rumor → kind 13 seal signed through the operator's signer → kind 1059
wrap from a throwaway key) to the operator's own account pubkey, or to
super_config.alerts_pubkey when set. Best-effort: a failed publish is
logged and the dispense report is still acked; the worklist is the
durable record. No email channel, no NIP-04.

notify.py

@@ -0,0 +1,202 @@
+"""
+Operator alerts over Nostr (bitspire ADR-005 §6 / Future directions).
+
+When a cash-out settlement lands in `cash_owed` or `partial_pending` — a
+customer has paid and is owed cash — the operator is told, immediately, as a
+Nostr event addressed to their pubkey. Not email, not SMS (lamassu's
+`notifyOperator` channel). The pieces this reuses:
+
+  - the recipient is the operator's own LNbits-account pubkey (`account.pubkey`,
+    which `get_machine_config` already refuses to run without), or
+    `super_config.alerts_pubkey` when set — a phone identity, say;
+  - the sender signs and NIP-44-encrypts through the operator's signer
+    (bunker-backed where the operator has moved to one), so no key is at rest
+    here. For the default recipient this is a note to self, which every NIP-46
+    client renders as a DM thread with yourself.
+
+Wire: NIP-17. A kind-14 rumor (unsigned) is sealed (kind 13, NIP-44 to the
+recipient, signed by the sender) and gift-wrapped (kind 1059, NIP-44 to the
+recipient, signed by a throwaway key, `p`-tagged to the recipient, stamped at
+a random moment in the last two days). The relay sees a throwaway pubkey and
+ciphertext; only the recipient can open it. NIP-04 is not used anywhere in
+this stack.
+
+Best-effort by contract: a failed alert is logged and never fails the RPC
+that triggered it — the dispense report must still be acknowledged, and the
+worklist is the durable record. `operator_notified_at` is set only on a
+successful publish, so a report resend cannot re-alert.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import json
+import random
+import time
+
+from loguru import logger
+
+from .crud import get_super_config, mark_settlement_notified
+from .models import DcaSettlement, DispenseReportIn, Machine
+from .nostr_publish import (
+    NostrPublishError,
+    nip44_encrypt_via_signer,
+    publish_signed_event,
+    resolve_operator_signer,
+    sign_as_operator,
+)
+
+KIND_DM = 14
+KIND_SEAL = 13
+KIND_GIFT_WRAP = 1059
+# NIP-17: randomise outer timestamps up to two days in the past so the wrap
+# does not reveal when the conversation happened.
+_MAX_BACKDATE_S = 2 * 24 * 60 * 60
+
+
+def _canonical_id(
+    pubkey: str, created_at: int, kind: int, tags: list, content: str
+) -> str:
+    from lnbits.utils.nostr import json_dumps
+
+    return hashlib.sha256(
+        json_dumps([0, pubkey, created_at, kind, tags, content]).encode()
+    ).hexdigest()
+
+
+def _backdated_now() -> int:
+    return int(time.time()) - random.randint(0, _MAX_BACKDATE_S)  # noqa: S311
+
+
+def _wrap_with_ephemeral(plaintext: str, recipient: str, created_at: int) -> dict:
+    """Kind-1059 gift wrap: NIP-44-encrypt `plaintext` to `recipient` from a
+    freshly generated key, sign with that key, and forget it."""
+    import coincurve
+    from lnbits.utils.nostr import generate_keypair, sign_event
+
+    from .nip44 import encrypt_for
+
+    priv_hex, pub_hex = generate_keypair()
+    wrap = {
+        "kind": KIND_GIFT_WRAP,
+        "created_at": created_at,
+        "tags": [["p", recipient]],
+        "content": encrypt_for(plaintext, priv_hex, recipient),
+    }
+    return sign_event(wrap, pub_hex, coincurve.PrivateKey(bytes.fromhex(priv_hex)))
+
+
+async def build_gift_wrapped_dm(
+    operator_user_id: str, recipient_pubkey_hex: str, text: str
+) -> dict:
+    """Build a NIP-17 gift-wrapped DM from the operator's identity to
+    `recipient_pubkey_hex`. Returns the signed kind-1059 event, ready to publish.
+
+    Raises the typed NostrPublishError subclasses from nostr_publish on a hard
+    failure (no pubkey on file, signer unavailable, …)."""
+    account, signer = await resolve_operator_signer(operator_user_id)
+    sender = account.pubkey
+    recipient = recipient_pubkey_hex.lower()
+
+    # 1. rumor — unsigned kind 14, id computed so clients can thread it
+    rumor_created = int(time.time())
+    rumor_tags = [["p", recipient]]
+    rumor = {
+        "id": _canonical_id(sender, rumor_created, KIND_DM, rumor_tags, text),
+        "pubkey": sender,
+        "created_at": rumor_created,
+        "kind": KIND_DM,
+        "tags": rumor_tags,
+        "content": text,
+    }
+
+    # 2. seal — NIP-44 to the recipient, signed by the sender (the bunker
+    #    path never sees the operator's key here)
+    sealed_content = await nip44_encrypt_via_signer(
+        account, signer, json.dumps(rumor, separators=(",", ":")), recipient
+    )
+    seal = {"kind": KIND_SEAL, "tags": [], "content": sealed_content}
+    seal = await sign_as_operator(operator_user_id, seal)
+
+    # 3. gift wrap — NIP-44 from a throwaway key to the recipient, p-tagged,
+    #    backdated, signed by that same throwaway key, which is then forgotten
+    return _wrap_with_ephemeral(
+        json.dumps(seal, separators=(",", ":")), recipient, _backdated_now()
+    )
+
+
+async def resolve_alert_recipient(operator_user_id: str) -> str:
+    """`super_config.alerts_pubkey` when set, else the operator's own pubkey."""
+    cfg = await get_super_config()
+    override = (getattr(cfg, "alerts_pubkey", None) or "").strip() if cfg else ""
+    if override:
+        return override.lower()
+    account, _signer = await resolve_operator_signer(operator_user_id)
+    return account.pubkey
+
+
+def format_cash_outcome_alert(
+    settlement: DcaSettlement, machine: Machine, report: DispenseReportIn, status: str
+) -> str:
+    """The message the operator reads on their phone. Plain text, the facts
+    they need to act, no raw dispenser code (that is in the dashboard)."""
+    name = machine.name or machine.id
+    paid = f"{report.fiat_cents / 100:.2f} {report.currency}"
+    out = f"{report.dispensed_fiat_cents / 100:.2f} {report.currency}"
+    if status == "cash_owed":
+        head = f"⚠️ CASH OWED — {name}"
+        body = f"A customer paid {paid} and received nothing."
+    else:
+        head = f"⚠️ PARTIAL DISPENSE — {name}"
+        body = f"A customer paid {paid} and received {out}."
+    lines = [
+        head,
+        body,
+        f"Cause: {report.error or 'no dispenser error reported'}"
+        + (f" ({report.error_code})" if report.error_code else ""),
+        f"Transaction: {report.txid}",
+        f"Settlement: {settlement.id}",
+        "Nothing has been distributed. Open spirekeeper → Worklist to resolve "
+        "(remediate at the machine, or settle off-machine).",
+    ]
+    if report.error_class == "terminal":
+        lines.append(
+            "The machine has taken cash-out out of service until you recount "
+            "or resume it."
+        )
+    return "\n".join(lines)
+
+
+async def notify_cash_outcome(
+    settlement: DcaSettlement,
+    machine: Machine,
+    report: DispenseReportIn,
+    status: str,
+) -> bool:
+    """Alert the operator that `settlement` needs a human. Best-effort:
+    returns True if the DM was published, False (after logging) otherwise.
+    Never raises — the caller is the dispense-report RPC and must ack."""
+    if getattr(settlement, "operator_notified_at", None):
+        return False
+    try:
+        recipient = await resolve_alert_recipient(machine.operator_user_id)
+        text = format_cash_outcome_alert(settlement, machine, report, status)
+        wrapped = await build_gift_wrapped_dm(machine.operator_user_id, recipient, text)
+        await publish_signed_event(wrapped)
+        await mark_settlement_notified(settlement.id)
+        logger.info(
+            f"spirekeeper: operator alerted ({status}) for settlement {settlement.id} "
+            f"→ {recipient[:12]}… (gift wrap {wrapped['id'][:12]}…)"
+        )
+        return True
+    except NostrPublishError as exc:
+        logger.warning(
+            f"spirekeeper: could not alert operator for settlement {settlement.id}: {exc} "
+            "— the worklist still has it"
+        )
+    except Exception as exc:  # never let an alert break the RPC
+        logger.error(
+            f"spirekeeper: unexpected error alerting operator for settlement "
+            f"{settlement.id}: {exc!r}"
+        )
+    return False