feat(hub): group names unique per owner, shown as name@owner

A group's identity stays its UUID. What changes is that "the name is
unique" — until now an unenforced expectation — becomes real, scoped to the
owner account, and the owner's username is surfaced so two groups called
"photos" on different nodes can be told apart.

Hub:
- `groups` gains a functional unique index `uq_groups_owner_name` on
  `(admin_id, lower(name))` (model + migration c3d4e5f6a7b8). The migration
  pre-flights: if the data already clashes it aborts and lists the
  offending (admin_id, name) pairs rather than renaming anyone's group.
  meshbay.org checked clean.
- `create_group` trims the name, rejects blank (422) and an owner-scoped
  case-insensitive clash (409), with an IntegrityError backstop for the
  race, and returns `owner_username`.
- `owner_username` added to `/v1/groups/mine`, `GET /v1/groups` (local
  rows), `POST /v1/groups/{id}/join`, `GET /v1/admin/groups`.

SPA:
- new `static/group-name.js` — `<GroupName name owner [inline]>` renders the
  name with the `@owner` handle on a smaller grey line under it.
- used in the sidebar, the group-page header, Explore cards, the Admin
  groups table, and cross-group Search (via a widened `cacheGroupIndex`
  carrying the owner). Delete/leave confirmations show `name@owner` inline.
- federated Explore rows show `@<source_hub>` instead of an account.

Design record and the locked decisions: ~/next/groupnames.md (out of repo).
MNP unchanged. Tests: test_group_name_unique.py, test_group_name_migration.py.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018gKJ85aZyvEwarXMFzFEwi

1 files changed, 64 insertions, 0 deletions

diff --git a/packages/meshbay-hub/tests/test_group_name_migration.py b/packages/meshbay-hub/tests/test_group_name_migration.py
new file mode 100644
index 0000000..9813e04
--- /dev/null
+++ b/packages/meshbay-hub/tests/test_group_name_migration.py
@@ -0,0 +1,64 @@
+"""
+The uq_groups_owner_name migration refuses to run over data that already
+violates it, naming the offending pairs — it must never silently rename a
+group.
+"""
+
+import sqlite3
+from pathlib import Path
+
+import pytest
+from alembic import command
+from alembic.config import Config
+
+HUB = Path(__file__).resolve().parents[1]
+BEFORE = "b1c2d3e4f5a6"
+AFTER = "c3d4e5f6a7b8"
+
+_USER = ("INSERT INTO users (id, username, email, pw_hash, pw_salt, hub_id) "
+         "VALUES ('u1', 'alice', 'a@x', x'00', x'00', 'h')")
+_GROUP = ("INSERT INTO groups (id, name, admin_id, visibility, join_policy, status) "
+          "VALUES (?, ?, 'u1', 'private', 'invite', 'active')")
+
+
+@pytest.fixture
+def at_before(tmp_path, monkeypatch):
+    """A hub DB migrated up to the revision just before uq_groups_owner_name."""
+    db = tmp_path / "hub.db"
+    monkeypatch.setenv("MESHBAY_DATABASE_URL", f"sqlite+aiosqlite:///{db}")
+    cfg = Config(str(HUB / "alembic.ini"))
+    command.upgrade(cfg, BEFORE)
+    return db, cfg
+
+
+def test_migration_aborts_on_a_pre_existing_duplicate(at_before):
+    db, cfg = at_before
+    con = sqlite3.connect(db)
+    con.execute(_USER)
+    con.execute(_GROUP, ("g1", "Photos"))
+    con.execute(_GROUP, ("g2", "photos"))     # same owner, same name bar case
+    con.commit()
+    con.close()
+
+    with pytest.raises(Exception) as exc:
+        command.upgrade(cfg, AFTER)
+    assert "uq_groups_owner_name" in str(exc.value)
+    assert "photos" in str(exc.value).lower()
+
+
+def test_migration_runs_when_data_is_clean(at_before):
+    db, cfg = at_before
+    con = sqlite3.connect(db)
+    con.execute(_USER)
+    con.execute(_GROUP, ("g1", "Photos"))
+    con.execute(_GROUP, ("g2", "Videos"))
+    con.commit()
+    con.close()
+
+    command.upgrade(cfg, AFTER)
+
+    con = sqlite3.connect(db)
+    idx = [r[0] for r in con.execute(
+        "SELECT name FROM sqlite_master WHERE type='index' AND tbl_name='groups'")]
+    con.close()
+    assert "uq_groups_owner_name" in idx