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taodengandClaude Opus 4.7 (noreply@anthropic.com)
5960486542
Phase 1 Day 6 — the architectural milestone of Phase 1. OLP is no longer
a single-provider proxy with cache; it is now a multi-provider router
with idempotent-failure-safe fallback. ADR 0004 ratified in v0.1 governance
is fully implemented for D9 scope. Configuration-driven chains activate
when a user populates ~/.olp/config.json routing.chains; at v0.1 default
(empty chains), behaviour is single-hop pass-through identical to D5.
Files:
NEW: lib/fallback/engine.mjs (~470 lines) — Trigger taxonomy, chain
advancement, first-chunk safety, observability annotation.
MOD: server.mjs (+80 lines net) — wires executeWithFallback between IR
construction and provider.spawn. Per-hop cache key isolation
(ADR 0005 § Cross-provider fallback). Test seams added:
__setFallbackConfig, __resetFallbackConfig, __clearCache.
MOD: test-features.mjs (+845 lines, 6 new suites = +55 tests).
Authority citations:
ADR 0004 § Decision § Trigger taxonomy — Hard / Soft / Deterministic
(deferred) / Cost-aware (deferred) implemented exactly per spec.
ADR 0004 § Decision § Fallback safety — first-chunk rule satisfied at
D9 by buffering composition (executeHopFn = collectAllChunks; server
writes to res only after engine returns).
ADR 0004 § Decision § Chain advancement — one-at-a-time iteration;
originalError preserved from FIRST hop (not last) on exhaustion.
ADR 0004 § Decision § No fallback for client-side errors — HTTP 400/
401/403/404/422 stop the chain immediately; AUTH_MISSING also stops
immediately (user-config failure, not provider-quota).
ADR 0004 § Decision § Observability headers — X-OLP-Fallback-Hops set
from engine return value; X-OLP-Fallback-Exhausted lists tried
providers on exhaustion.
ADR 0005 § Cross-provider fallback cache behavior — each fallback hop
computes a fresh cache key with the hop's (provider, model) tuple;
primary's cache entries cannot leak to secondary's hop.
Reviewer chain (Iron Rule 10):
Implementer: sonnet (general-purpose).
Fresh-context reviewer: opus. Verdict APPROVE_WITH_MINOR.
Reviewer ran npm test (277/277 pass), read ADR 0004 + ADR 0005 end-
to-end, verified first-chunk-safety composition, checked all
trigger taxonomy mappings.
Reviewer non-blocking findings folded in this commit:
1. Test label at test-features.mjs:3756 clarified. Original title
"client error (400) → does NOT fall back" was misleading because
the test actually exercises both-fail SPAWN_FAILED → exhausted
path (400-no-fallback semantic is covered at unit level instead).
Renamed + commented to match actual behaviour.
2. triedProviders semantic (includes soft-skipped) documented in
engine.mjs comment near the soft-trigger branch.
3. SOFT_TRIGGER synthetic code documented in engine.mjs as engine-
internal, NOT a member of base.mjs PROVIDER_ERROR_CODES.
Reviewer non-blocking suggestions deferred (open D-later questions):
- Q1 cacheStatus on fallback hops: conservative 'miss', acceptable
per ADR 0005 § Per-model isolation.
- Q2 X-OLP-Fallback-Exhausted only when triedProviders > 1:
acceptable per ADR 0004 spec.
- Q3 soft-trigger quotaSnapshot always null at D9: acceptable per
ADR 0004 § Consequences/Negative graceful-degrade clause. Phase 2
will add quota poll-worker.
- Q4 loadFallbackConfigSync sync-only: acceptable for bounded
startup I/O.
Test count: 222 (D8) → 277 (D9). 6 new test suites cover trigger
taxonomy, engine chain advancement (including the load-bearing
originalError-from-FIRST-hop property), HTTP integration through
real server.mjs, soft trigger pre-fetch path, exhausted-chain
header emission.
Verification:
node --check on all touched files: clean.
npm test on Node 25.8.0: 277/277 pass in 266ms.
Hygiene grep: zero personal-name/path/token hits.
No new external npm deps.
Co-Authored-By: Claude Opus 4.7 (noreply@anthropic.com)