Three items from operator feedback after running the actual flow:
(1) Help docstring lied: "--bucket / --source-table ignored" for
materialized rows. Reality: --bucket is load-bearing because
`agnes schema <name>` builds the BQ identifier as
`bq.<bucket>.<source_table>`. An empty bucket registered the row but
broke schema/describe with HTTP 400 "unsafe BQ identifier in
registry". Fix: docstring rewritten to reflect reality, plus
client-side validation rejects materialized + empty bucket with a
clear error pointing at the right knob.
(2) Post-register UX cliff: `agnes pull` after register-table reports
"Updated 0 tables (1 total)" because registration adds a registry
row but does NOT trigger a parquet build. Operators routinely
assume something's broken when they need to run
`agnes setup first-sync` to kick off the materialization. Hint
emitted on success now points at first-sync.
(3) RBAC gotcha: `agnes catalog` is RBAC-filtered via
`resource_grants`, so non-admin users don't see freshly-registered
rows until a grant is created. Hint emitted on success now points at
`agnes admin grant create <group> table <name>`.
Tests: 8/8 in test_cli_admin_materialized.py, including two new
regression tests for the validation + the hint output.