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.
Implementation confirmed that no invalid GatewaySettings instance can exist, so
the factory test's exception fires while evaluating the argument rather than
inside from_settings. Recorded so the test is not misread as the factory
carrying its own validation.
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'.
AIMD ceiling now respects per-source max_concurrency and the pacer is
assembled explicitly in the client; MIN_CALLS parses as strict int;
acceptance doc corrects source-5 attempt count to 549; design and
migration notes aligned with implemented 429/stall/suppression
semantics and AIMD constants documented.
Round 8 forensics caught the healthy source circuit-opened by five
random empty completions (~20% ambient failure rate makes a 5-streak
land every ~3000 attempts), blacking out the only good source for 60s.
When the window holds min_calls samples below the failure-rate
threshold, a streak is noise and no longer opens the gate; cold-start
and low-traffic semantics are unchanged and sudden death of a warm
source is still caught by the rate channel.
Round 6 hit account-level rate throttling the concurrency AIMD cannot
absorb: at 26 req/min the gateway still returned 16% 429s and each one
burned a third of the retry budget. Retry-After-guided 429s now back
off without consuming attempts (gRPC pushback semantics); the retry
loop gains a per-call ceiling using the same dual-condition stall
verdict as quota-wait (local window exceeded AND no global progress).
Round 5 left three residual failure classes; ladder exhaustion (3.2%
of structured calls with a single re-ask) and 429 leakage (5.8%, AIMD
oscillating above the sustainable point) are addressable: re-ask
default goes 1 to 2 (conservative vs instructor's 3) and the AIMD cut
factor drops to 0.5.
Round 3 showed unconditional yield-after-two-failures pushes the third
attempt onto known-bad sources in heterogeneous pools (83% vs 10%
expected success). OutcomeAwareSelector now exposes health(); a failed
source only yields when some untried candidate scores at least half its
health. Health-blind selectors keep the unconditional rule.
P6 round 2 showed routing convergence turns account-level 429s into
the binding constraint (62% throttle rate at full concurrency). Each
source now carries a local AIMD limit: multiplicative cut on 429,
additive growth on success. Over-limit picks queue via the existing
quota-wait poll instead of burning retry budget or tripping the
circuit-open verdict.
Classify empty completions as transient per human ruling (fixes flaky
real-gateway smoke and prevents caching empty responses), rename the
factory injection parameter gate to breaker per the frozen design,
rewrite the probe-entry cleanup without except BaseException, declare
python-dotenv explicitly, add a mid-backoff cancellation test, and
record all implementation errata in the design and architecture docs.
Also note that the seven architecture amendments predate the plan,
tighten T12 to independent implementation layers, and add fallback
guidance for read-only reference protocol imports.
iomgaa