fix: complete the unpaired-machine sweep + regression test

Full sweep of every machine_npub deref found one more reachable crash:
_record_rejected (tasks.py) logs machine_npub[:12], and the
assert_nostr_attribution guard now routes an unpaired machine there, so
None[:12] -> TypeError. Fall back to machine.id.

Every other deref is safe by the attribution-gate invariant: a settlement only
flows past assert_nostr_attribution (now rejecting unpaired) for a paired
machine, so the downstream distribution / parse-path / "landed" logs can't see
None; the collision-loop display already uses `(m.machine_npub or m.id)`.

Adds tests/test_unpaired_machine_guards.py: attribution rejects an unpaired
machine with the domain SettlementAttributionError (not AttributeError), and
build_state_d_tags skips it. New tests + every guard-affected suite pass.

(Two pre-existing test_pair_endpoint failures — #29 drift: fake_pair lacks
bunker_relay, and the test DB lacks super_config — are out of scope; filed
separately.)

tasks.py

@@ -235,7 +235,10 @@ async def _record_rejected(payment: Payment, machine: Machine, exc: Exception) -
         return
     logger.error(
         f"spirekeeper: rejected settlement {rejected.id} "
-        f"(machine={machine.machine_npub[:12]}..., "
+        # An unpaired machine (machine_npub None) reaches here now that
+        # assert_nostr_attribution rejects it — fall back to the id so the
+        # log line doesn't crash on None[:12].
+        f"(machine={(machine.machine_npub or machine.id)[:12]}..., "
         f"payment_hash={payment.payment_hash[:12]}...): {exc}"
     )
 

tests/test_unpaired_machine_guards.py

@@ -0,0 +1,57 @@
+"""
+Regression: `machine_npub` is nullable (#29/m011 register-unpaired flow), so
+every consumer that derives a Nostr identity from it must handle `None` rather
+than crash `normalize_public_key(None)` (AttributeError: 'NoneType' has no
+'startswith') or `machine_npub[:12]` (TypeError). See PR #33 — an unpaired
+machine on the demo broke the platform-fee update (500) and the cassette
+consumer.
+
+These cover the pure-function guards; the DB-backed loops
+(get_machine_by_atm_pubkey_hex, the super-config republish loop) are exercised
+on the dev stack with an unpaired active machine.
+"""
+
+from datetime import datetime, timezone
+
+import pytest
+
+from ..bitspire import SettlementAttributionError, assert_nostr_attribution
+from ..cassette_transport import build_state_d_tags_for_machines
+from ..models import Machine
+
+_PAIRED_HEX = "82341f882b6eabcbd6b1c2da5cd14df14b8e91dd0e6da41a72b78ad8f3a7d3b9"
+
+
+def _machine(npub: str | None) -> Machine:
+    now = datetime.now(timezone.utc)
+    return Machine(
+        id="unpaired1",
+        operator_user_id="op1",
+        machine_npub=npub,
+        wallet_id="w1",
+        name="unpaired",
+        location=None,
+        fiat_code="EUR",
+        is_active=True,
+        created_at=now,
+        updated_at=now,
+    )
+
+
+def test_attribution_rejects_unpaired_machine_cleanly():
+    """An unpaired machine must raise the domain SettlementAttributionError
+    (which the listener records as 'rejected'), not an uncaught AttributeError
+    from normalize_public_key(None)."""
+    with pytest.raises(SettlementAttributionError):
+        assert_nostr_attribution(
+            _machine(None),
+            {"source": "bitspire", "nostr_sender_pubkey": _PAIRED_HEX},
+        )
+
+
+def test_cassette_d_tags_skip_unpaired_machine():
+    """build_state_d_tags_for_machines must skip unpaired machines rather than
+    crash _atm_hex_pubkey on a None npub — the cassette-consumer loop crash."""
+    tags = build_state_d_tags_for_machines([_machine(_PAIRED_HEX), _machine(None)])
+    assert len(tags) == 1  # only the paired machine contributes a d-tag
+    assert all("None" not in t for t in tags)