Round two of the from_env-only validation problem. Fifteen checks still lived
in the env parsing functions: six enum domains, the redis_url requirement for
redis-backed limiter/breaker/cache, cache namespace and TTL, telemetry path and
DSN, non-negative structured retries and non-blank scope. from_settings and
direct construction bypassed all of them.
The five asserts in client.py that claimed config had already validated
redis_url and the telemetry targets now hold on every path, so they revert to
what CLAUDE.md permits: internal invariant declarations that also narrow the
Optional for type checkers. Their comments now name the method that guarantees
them, since the previous wording is exactly what went stale.
Postgres DSNs built by hand now get the SQLAlchemy +driver suffix stripped the
way from_env has always stripped it, with a warning so the rewrite is not
silent. The env path strips earlier, so it stays quiet.
Corrects the changelog claim that the old guard messages only named env keys:
they named fields too, it was the remediation advice that pointed at env keys.
Records the human approval of the design, the mutation-testing evidence from
the independent verifier, and the same-class gap it found: 14 checks (redis_url
presence, telemetry paths, enum validity) still live only in from_env, while
client.py asserts they were already validated. Deliberately out of scope here.
Patch release for the settings invariant fix. The changelog carries a separate
'behaviour tightening' section because a patch number gives downstreams no
warning that construction can now raise where it previously did not.
iomgaa