feat(pairing): slim the spire seed + carry lnbits_npub (bitspire-#70)

Mint the new-shape seed the bitspire consumer now expects: the pubkey rides
once as spire_npub (consumer derives the hex + reconstructs bunker_url from
bunker_secret + bunker_relay|relays[0]), and lnbits_npub is embedded so a paired
machine reaches this lnbits' nostr-transport with nothing else provisioned.

- build_seed_url emits {spire_npub, lnbits_npub, bunker_secret, relays} and
  bunker_relay only when it differs from relays[0] (omitted in the common case).
  Drops spire_pubkey + the full bunker_url from the payload.
- pair_spire reads settings.nostr_transport_public_key, hex_to_npub's it, and
  raises PairingError when it's empty (transport not running → can't mint a
  self-sufficient seed). bunker_url is still returned in PairResult for operator
  display / audit; only the seed stops embedding it.

Consumer side: bitspire packages/nostr-client/src/seed.ts + the #70 machine
wiring. Kept as v: 1 (redefined in place; no shipped seed to preserve).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

pairing.py

@@ -23,15 +23,21 @@ We deliberately do NOT run the connect/eager-bind step here: the spire is the
 NIP-46 client, so the binding must happen spire-side with the spire's own
 client keypair. spirekeeper only mints + packages.
 
-Seed URL wire format (contract shared with bitspire#52):
+Seed URL wire format (contract shared with bitspire#52, slimmed in bitspire#70):
 
     spire-seed:v1:<base64url(json)>      json = {
         "v": 1,
-        "spire_npub":   "npub1…",         # the bunker-minted spire identity
-        "spire_pubkey": "<64-hex>",       # same key, hex (consumer convenience)
-        "bunker_url":   "bunker://<spire_pubkey>?relay=<bunker_relay>&secret=<sec>",
-        "relays":       ["wss://…"],      # relays for the spire's own events
+        "spire_npub":    "npub1…",        # the bunker-minted spire identity
+        "lnbits_npub":   "npub1…",        # this lnbits' nostr-transport server id
+        "bunker_secret": "<sec>",         # one-shot NIP-46 connect token
+        "relays":        ["wss://…"],     # relays for the spire's own events
+        "bunker_relay":  "wss://…",       # OPTIONAL — omitted when == relays[0]
     }
+
+The pubkey is carried ONCE, as an npub: the consumer derives spire_pubkey (hex)
+and reconstructs the bunker:// URL from spire_npub + bunker_relay|relays[0] +
+bunker_secret. `lnbits_npub` lets a paired machine reach this lnbits' transport
+with nothing else provisioned. See bitspire packages/nostr-client/src/seed.ts.
 """
 
 from __future__ import annotations
@@ -48,6 +54,7 @@ from lnbits.core.services.nsec_bunker import (
 )
 from lnbits.core.signers.remote_bunker import ensure_policy
 from lnbits.settings import settings
+from lnbits.utils.nostr import hex_to_npub
 from pydantic import BaseModel
 
 from .models import Machine
@@ -136,15 +143,27 @@ def _recover_token(tokens: list[dict], client_name: str) -> str:
 
 
 def build_seed_url(
-    *, spire_npub: str, spire_pubkey_hex: str, bunker_url: str, relays: list[str]
+    *,
+    spire_npub: str,
+    lnbits_npub: str,
+    bunker_secret: str,
+    relays: list[str],
+    bunker_relay: str | None = None,
 ) -> str:
-    payload = {
+    """Build the slim seed URL (bitspire#70). The pubkey rides once as
+    `spire_npub`; the consumer derives the hex + reconstructs `bunker_url` from
+    `bunker_secret` + `bunker_relay` (or `relays[0]`). `bunker_relay` is emitted
+    only when it differs from `relays[0]`, keeping the common case one field
+    lighter."""
+    payload: dict = {
         "v": 1,
         "spire_npub": spire_npub,
-        "spire_pubkey": spire_pubkey_hex,
-        "bunker_url": bunker_url,
+        "lnbits_npub": lnbits_npub,
+        "bunker_secret": bunker_secret,
         "relays": relays,
     }
+    if bunker_relay and relays and bunker_relay != relays[0]:
+        payload["bunker_relay"] = bunker_relay
     blob = (
         base64.urlsafe_b64encode(json.dumps(payload, separators=(",", ":")).encode())
         .decode()
@@ -233,15 +252,31 @@ async def pair_spire(
     token = _recover_token(tokens, client_name)
     _, _, secret = token.partition("#")
 
+    # The spire needs THIS lnbits' nostr-transport server identity to reach the
+    # backend from the seed alone (bitspire#70). The transport sets
+    # `settings.nostr_transport_public_key` at startup; if it's empty the
+    # transport isn't running, so we can't mint a self-sufficient seed.
+    lnbits_pubkey_hex = settings.nostr_transport_public_key
+    if not lnbits_pubkey_hex:
+        raise PairingError(
+            "LNbits nostr transport has no server pubkey "
+            "(settings.nostr_transport_public_key is empty) — is the transport "
+            "running? Cannot mint a self-sufficient seed."
+        )
+    lnbits_npub = hex_to_npub(lnbits_pubkey_hex)
+
+    # bunker_url is still returned in PairResult (operator display / audit); the
+    # seed itself no longer embeds it — the consumer reconstructs it.
     bunker_url = (
         f"bunker://{spire_pubkey_hex}?relay={quote(relay, safe='')}"
         f"&secret={quote(secret, safe='')}"
     )
     seed_url = build_seed_url(
         spire_npub=spire_npub,
-        spire_pubkey_hex=spire_pubkey_hex,
-        bunker_url=bunker_url,
+        lnbits_npub=lnbits_npub,
+        bunker_secret=secret,
         relays=relays,
+        bunker_relay=relay,
     )
     return PairResult(
         spire_npub=spire_npub,

tests/test_pairing.py

@@ -17,6 +17,7 @@ from datetime import datetime, timezone
 
 import pytest
 from lnbits.core.services.nsec_bunker import NsecBunkerError
+from lnbits.settings import settings
 from lnbits.utils.nostr import hex_to_npub
 
 from ..models import Machine
@@ -35,11 +36,23 @@ from ..pairing import (
 _NOW = datetime(2026, 6, 16, tzinfo=timezone.utc)
 _SPIRE_HEX = "522a4538f1df96508d9ee8b14072344dd4a566acfe03c25a92a39179c6fca891"
 _SPIRE_NPUB = hex_to_npub(_SPIRE_HEX)
+_LNBITS_HEX = "b0b1b2b3b4b5b6b7b8b9babbbcbdbebfc0c1c2c3c4c5c6c7c8c9cacbcccdcecf"
+_LNBITS_NPUB = hex_to_npub(_LNBITS_HEX)
 _RELAYS = ["wss://lnbits.demo.aiolabs.dev/nostrrelay/demo"]
 _BUNKER_RELAY = "wss://bunker.internal/relay"
 _PASSPHRASE = "keystore-pass"  # pragma: allowlist secret
 
 
+@pytest.fixture(autouse=True)
+def _set_transport_pubkey():
+    # pair_spire reads this lnbits' nostr-transport server pubkey to embed
+    # lnbits_npub in the seed (bitspire#70). Set it for every test; restore after.
+    prev = settings.nostr_transport_public_key
+    settings.nostr_transport_public_key = _LNBITS_HEX
+    yield
+    settings.nostr_transport_public_key = prev
+
+
 @pytest.fixture(autouse=True)
 def _clear_policy_cache():
     # lnbits' ensure_policy caches resolved policy ids on
@@ -157,18 +170,28 @@ def test_bunker_url_carries_pubkey_relay_secret():
     assert "secret=topsecret" in result.bunker_url
 
 
+def _decode_seed(seed_url: str) -> dict:
+    assert seed_url.startswith(SEED_URL_SCHEME)
+    blob = seed_url[len(SEED_URL_SCHEME) :]
+    return json.loads(base64.urlsafe_b64decode(blob + "=" * (-len(blob) % 4)))
+
+
 def test_seed_url_decodes_to_contract():
+    # _pair passes an explicit bunker_relay distinct from relays[0], so it's
+    # carried; the pubkey rides once as spire_npub, lnbits_npub is embedded,
+    # and neither spire_pubkey nor bunker_url appears (bitspire#70).
     result = _pair(FakeBunker(token_secret="zzz"))  # pragma: allowlist secret
-    assert result.seed_url.startswith(SEED_URL_SCHEME)
-    blob = result.seed_url[len(SEED_URL_SCHEME) :]
-    payload = json.loads(base64.urlsafe_b64decode(blob + "=" * (-len(blob) % 4)))
+    payload = _decode_seed(result.seed_url)
     assert payload == {
         "v": 1,
         "spire_npub": _SPIRE_NPUB,
-        "spire_pubkey": _SPIRE_HEX,
-        "bunker_url": result.bunker_url,
+        "lnbits_npub": _LNBITS_NPUB,
+        "bunker_secret": "zzz",
         "relays": _RELAYS,
+        "bunker_relay": _BUNKER_RELAY,
     }
+    assert "spire_pubkey" not in payload
+    assert "bunker_url" not in payload
 
 
 def test_fresh_policy_adds_kindless_nip44_rules():
@@ -266,14 +289,40 @@ def test_missing_relay_or_passphrase_raises():
 def test_build_seed_url_roundtrip():
     url = build_seed_url(
         spire_npub=_SPIRE_NPUB,
-        spire_pubkey_hex=_SPIRE_HEX,
-        bunker_url="bunker://x?relay=r&secret=s",
+        lnbits_npub=_LNBITS_NPUB,
+        bunker_secret="s",  # pragma: allowlist secret
         relays=_RELAYS,
+        bunker_relay=_BUNKER_RELAY,
     )
-    blob = url[len(SEED_URL_SCHEME) :]
-    payload = json.loads(base64.urlsafe_b64decode(blob + "=" * (-len(blob) % 4)))
-    assert payload["spire_pubkey"] == _SPIRE_HEX
+    payload = _decode_seed(url)
+    assert payload["spire_npub"] == _SPIRE_NPUB
+    assert payload["lnbits_npub"] == _LNBITS_NPUB
+    assert payload["bunker_secret"] == "s"
     assert payload["relays"] == _RELAYS
+    assert payload["bunker_relay"] == _BUNKER_RELAY
+
+
+def test_build_seed_url_omits_default_bunker_relay():
+    # bunker_relay omitted when it equals relays[0] (or is None) — the consumer
+    # defaults it to relays[0], so carrying it would be redundant bytes.
+    for same in (_RELAYS[0], None):
+        payload = _decode_seed(
+            build_seed_url(
+                spire_npub=_SPIRE_NPUB,
+                lnbits_npub=_LNBITS_NPUB,
+                bunker_secret="s",  # pragma: allowlist secret
+                relays=_RELAYS,
+                bunker_relay=same,
+            )
+        )
+        assert "bunker_relay" not in payload
+
+
+def test_pair_missing_transport_pubkey_raises():
+    # No transport server pubkey → can't mint a self-sufficient seed.
+    settings.nostr_transport_public_key = ""
+    with pytest.raises(PairingError, match="transport"):
+        _pair(FakeBunker())
 
 
 def test_pair_threads_duration_hours():