feat(hub): one account, several linked nodes

An account links up to MAX_NODES_PER_ACCOUNT node keys (node_keys table)
instead of the one users.pk_node_ed25519; the migration carries each
account's key over and the downgrade keeps the last one linked.
/v1/nodes/auth accepts any linked key, and its token names the key that
won it (nk). PUT /me/node_key adds a key, idempotently, 409 past the
limit; DELETE /me/node_key names the key: a browser session any of its
own, a node only its own. Unlinking a key closes that node's socket and
refuses its tokens at once, on REST and on the socket; the account's other
nodes are untouched. /pubkeys no longer gives a node key to other accounts,
and gives the caller its last linked one, which installed desktop apps read.

The node reports waiting_for_node_key while its key is unlinked and signs
in again as soon as the hub says so, so a key linked again is back within
seconds; unlinking itself signs in first to hold a token naming its key.

Profile -> Linked nodes lists each node (connected, last seen, IP, linked
since, This machine in the desktop app) with Copy and Unlink, and adds a
key by hand. The Node page banner, Create group and the desktop app add
this machine's key instead of replacing another's. Messages that pointed
at Settings -> Link Node point at Profile -> Linked nodes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 63 insertions, 0 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/db/migrations/versions/f8a9b0c1d2e3_node_keys.py b/packages/meshbay-hub/src/meshbay_hub/db/migrations/versions/f8a9b0c1d2e3_node_keys.py
new file mode 100644
index 0000000..b02167b
--- /dev/null
+++ b/packages/meshbay-hub/src/meshbay_hub/db/migrations/versions/f8a9b0c1d2e3_node_keys.py
@@ -0,0 +1,63 @@
+"""several node keys per account: one per machine the person runs a node on
+
+Revision ID: f8a9b0c1d2e3
+Revises: e7f8a9b0c1d2
+"""
+
+import uuid
+from collections.abc import Sequence
+from datetime import UTC, datetime
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "f8a9b0c1d2e3"
+down_revision: str | Sequence[str] | None = "e7f8a9b0c1d2"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    node_keys = op.create_table(
+        "node_keys",
+        sa.Column("id", sa.String(36), primary_key=True),
+        sa.Column("user_id", sa.String(36), sa.ForeignKey("users.id"), nullable=False),
+        sa.Column("pk_node_ed25519", sa.String(64), nullable=False),
+        sa.Column("linked_at", sa.DateTime(timezone=True)),
+    )
+    op.create_index("uq_node_keys_user_key", "node_keys",
+                    ["user_id", "pk_node_ed25519"], unique=True)
+
+    # The key each account had linked keeps working: it becomes that account's
+    # first row, so no node has to be linked again after the upgrade.
+    conn = op.get_bind()
+    linked = conn.execute(sa.text(
+        "SELECT id, pk_node_ed25519 FROM users WHERE pk_node_ed25519 IS NOT NULL "
+        "AND pk_node_ed25519 <> ''")).fetchall()
+    now = datetime.now(UTC)
+    if linked:
+        op.bulk_insert(node_keys, [
+            {"id": str(uuid.uuid4()), "user_id": uid, "pk_node_ed25519": pk,
+             "linked_at": now}
+            for uid, pk in linked])
+
+    with op.batch_alter_table("users") as batch:
+        batch.drop_column("pk_node_ed25519")
+
+
+def downgrade() -> None:
+    with op.batch_alter_table("users") as batch:
+        batch.add_column(sa.Column("pk_node_ed25519", sa.String(64), nullable=True))
+
+    # One column holds one key: the most recently linked one is kept, which is
+    # the node the account would have had linked last before this revision.
+    conn = op.get_bind()
+    rows = conn.execute(sa.text(
+        "SELECT user_id, pk_node_ed25519 FROM node_keys ORDER BY linked_at")).fetchall()
+    latest = {uid: pk for uid, pk in rows}
+    for uid, pk in latest.items():
+        conn.execute(sa.text("UPDATE users SET pk_node_ed25519 = :pk WHERE id = :uid"),
+                     {"pk": pk, "uid": uid})
+
+    op.drop_index("uq_node_keys_user_key", table_name="node_keys")
+    op.drop_table("node_keys")