test: cover legacy key fallback

src/nostr/client.py

@@ -510,13 +510,16 @@ class NostrClient:
             self.current_manifest_id = ident
         return manifest, chunks
 
-    async def fetch_latest_snapshot(self) -> Tuple[Manifest, list[bytes]] | None:
-        """Retrieve the latest manifest and all snapshot chunks."""
-        if self.offline_mode or not self.relays:
-            return None
-        await self._connect_async()
+    async def _fetch_manifest_with_keys(
+        self, keys_obj: Keys
+    ) -> tuple[Manifest, list[bytes]] | None:
+        """Attempt to retrieve the manifest and chunks using ``keys_obj``.
 
-        self.last_error = None
+        ``self.keys`` is updated to ``keys_obj`` so that subsequent chunk and
+        delta downloads use the same public key that succeeded.
+        """
+
+        self.keys = keys_obj
         pubkey = self.keys.public_key()
         identifiers = [
             f"{MANIFEST_ID_PREFIX}{self.fingerprint}",
@@ -560,6 +563,36 @@ class NostrClient:
             # manifest was found but chunks missing; do not try other identifiers
             return None
 
+        return None
+
+    async def fetch_latest_snapshot(self) -> Tuple[Manifest, list[bytes]] | None:
+        """Retrieve the latest manifest and all snapshot chunks."""
+        if self.offline_mode or not self.relays:
+            return None
+        await self._connect_async()
+
+        self.last_error = None
+
+        try:
+            primary_keys = Keys.parse(self.key_manager.keys.private_key_hex())
+        except Exception:
+            primary_keys = self.keys
+
+        result = await self._fetch_manifest_with_keys(primary_keys)
+        if result is not None:
+            return result
+
+        try:
+            legacy_keys = self.key_manager.generate_legacy_nostr_keys()
+            legacy_sdk_keys = Keys.parse(legacy_keys.private_key_hex())
+        except Exception as e:
+            self.last_error = str(e)
+            return None
+
+        result = await self._fetch_manifest_with_keys(legacy_sdk_keys)
+        if result is not None:
+            return result
+
         if self.last_error is None:
             self.last_error = "Snapshot not found on relays"
 

src/tests/test_nostr_legacy_key_fallback.py

@@ -0,0 +1,86 @@
+import asyncio
+import base64
+import hashlib
+import json
+
+from helpers import DummyEvent, DummyFilter, dummy_nostr_client
+from nostr.backup_models import KIND_MANIFEST, KIND_SNAPSHOT_CHUNK
+from nostr.client import MANIFEST_ID_PREFIX
+from nostr_sdk import Keys
+
+
+def test_fetch_snapshot_legacy_key_fallback(dummy_nostr_client, monkeypatch):
+    client, relay = dummy_nostr_client
+
+    # Track legacy key generation
+    called = {"legacy": False}
+
+    class LegacyKeys:
+        def private_key_hex(self):
+            return "3" * 64
+
+        def public_key_hex(self):
+            return "4" * 64
+
+    def fake_generate():
+        called["legacy"] = True
+        return LegacyKeys()
+
+    monkeypatch.setattr(
+        client.key_manager, "generate_legacy_nostr_keys", fake_generate, raising=False
+    )
+
+    expected_pubkey = Keys.parse("3" * 64).public_key()
+
+    class RecordingFilter(DummyFilter):
+        def author(self, pk):
+            self.author_pk = pk
+            return self
+
+    monkeypatch.setattr("nostr.client.Filter", RecordingFilter)
+
+    chunk_bytes = b"chunkdata"
+    chunk_hash = hashlib.sha256(chunk_bytes).hexdigest()
+    manifest_json = json.dumps(
+        {
+            "ver": 1,
+            "algo": "gzip",
+            "chunks": [
+                {
+                    "id": "seedpass-chunk-0000",
+                    "size": len(chunk_bytes),
+                    "hash": chunk_hash,
+                    "event_id": None,
+                }
+            ],
+        }
+    )
+    manifest_event = DummyEvent(
+        KIND_MANIFEST, manifest_json, tags=[f"{MANIFEST_ID_PREFIX}fp"]
+    )
+    chunk_event = DummyEvent(
+        KIND_SNAPSHOT_CHUNK,
+        base64.b64encode(chunk_bytes).decode("utf-8"),
+        tags=["seedpass-chunk-0000"],
+    )
+
+    call = {"count": 0, "authors": []}
+
+    async def fake_fetch_events(f, _timeout):
+        call["count"] += 1
+        call["authors"].append(getattr(f, "author_pk", None))
+        if call["count"] <= 2:
+            return type("R", (), {"to_vec": lambda self: []})()
+        elif call["count"] == 3:
+            return type("R", (), {"to_vec": lambda self: [manifest_event]})()
+        else:
+            return type("R", (), {"to_vec": lambda self: [chunk_event]})()
+
+    monkeypatch.setattr(relay, "fetch_events", fake_fetch_events)
+
+    result = asyncio.run(client.fetch_latest_snapshot())
+    assert called["legacy"]
+    assert result is not None
+    manifest, chunks = result
+    assert b"".join(chunks) == chunk_bytes
+    assert call["authors"][-1].to_hex() == expected_pubkey.to_hex()