The independent verifier found 15 more checks still living only in from_env:
six enum domains, seven conditional-required pairs and two scalar ranges.
More severe than round one because client.py has five asserts that claim
config already validated the redis_url and telemetry paths, which is false on
the from_settings path.
Also records a normalisation gap the verifier missed: _load_pg_dsn strips the
SQLAlchemy +asyncpg suffix, so a hand-built DSN reaches asyncpg unstripped.
Guards for the three cross-field invariants (source timeout vs lease TTL,
stall window vs max TTFT, probe TTL vs slowest timeout) only ran inside
from_env, so the from_settings path could build a GatewaySettings that
violates the class's own documented invariants. Design moves all of them
plus a non-empty sources check into __post_init__ as _validate_* methods,
matching the existing frozen dataclasses in types.py.
Covers two defects left by PR#1: probe_ttl_s was never moved, and an empty
sources tuple leaked a bare 'max() arg is an empty sequence'.
Records the human decision to test against the real gateway with real
data instead of building a mock gateway, six execution scenarios with
fault-source mixing, hard invariants scored from our own telemetry,
and the corpus inventory pulled from the lab server.
iomgaa