The guard on names that reach SQL as identifiers rather than as bind parameters.

Almost everything Ergon sends to PostgreSQL is parameterised. A few things cannot be, and they are the reason this module exists:

• pgmq derives pgmq.q_<queue> from a queue name, and the notify tick builds its visibility probe with format('%I').
• ergon_migration bakes a table name into auto_manage_partitions_<table>, and into CREATE TABLE statements generally.
• ergon_partition_boot_check calls that function by name, and a function cannot be addressed by bind parameter.

In each case the name is host-authored rather than user input, so this is not the last line of defence. It is the cheap one: rejecting anything that could need quoting is simpler to reason about than quoting correctly everywhere, and it fails at the call site rather than inside a format/2 three layers down.

Deliberately stricter than PostgreSQL's own rules, which permit quoted identifiers containing almost anything. Ergon allows only what never needs quoting in the first place.