The Architect's Builders Review: pi-mega-compact EP2.

Four days. That's the delta. July 31 to August 5. Version 0.11.13 to 0.20.22. Forty releases. Two hundred and seventy commits. Three hundred and sixty-three thousand lines of TypeScript across nineteen hundred files. And an entirely new architectural layer — the Vector Cortex — twenty-seven sprints, VC0 through VC8, shipped and complete as of the morning of recording.

This is episode one of "Then vs Now," a new ArchitectIT format where we review a project, wait, and measure the delta. The thesis: in the age of AI-assisted development, the interesting unit of time isn't the quarter or the sprint — it's the week. What can change in a week? What actually ships? What holds up?

Pi-mega-compact is a local context compression extension for the pi coding agent. Fully local, zero telemetry, no external API calls — a hard invariant called PREVENT-PI-004 enforced by a static scanner. It manages your context window so long coding sessions don't blow up: compressing, deduplicating, and recalling conversation history with a three-stage Trident pipeline, three-layer semantic dedup, and a RAPTOR memory hierarchy. On July 31, it was the most sophisticated open-source context management tool we'd seen. In the first episode, we did a full architecture breakdown and a gap analysis. Four gaps were identified. All four are now closed.

The RAG suite — spec-only on July 31 — is shipped. Query reformulation with TF-IDF and Reciprocal Rank Fusion. Tiered routing across L0 in-memory cache, L1 FTS5 trigram, and L2 PGlite HNSW. CRAG quality metrics. HyDE auto-activation. Provider prompt cache visibility — the gap we called embarrassing — is now a full cache economics system with a crystal compiler that models cache hit and miss patterns as actionable economic signals, plus diagnostics and breakers that trip when cache poisoning is detected. The dashboard — flagged as overengineered — was completely rebuilt with Tailwind, shadcn, Playwright smoke tests, and a settings panel. Dedup thresholds now have audit logging, false-positive rate tracking, and a soft-as-hard headroom gate.

The Vector Cortex is the headline. A new architectural layer above the compression engine: a causal cache and proof system with twenty-seven sprints across nine phases. Baseline observability. Canonical event ledger with occurrence tracking. Multi-head encoder contract with deferred ML gate. Deterministic cortical topology with graph queries. Dual-tier semantic and exact shards with mandatory reconstruction fidelity. A prompt DAG with budgeted portfolio planning. Closure optimization with transitive reduction. Exact source restoration. A self-healing derived controller with fifteen healing scenarios. Frozen range cache crystals. Provider cache economics. Cache diagnostics with breakers. A consent-bound outcome ledger. A shadow adaptive policy engine with a bounded action set. And a Rust parity artifact — a second implementation that proves the TypeScript output is byte-identical and reproducible. Six named migrations with downgrade export. A triad A/B/C resilience model with a six-state breaker state machine, write-ahead logging, and chaos tests. A statistical evaluation framework with powered non-inferiority testing, stratified bootstrap, and rollout gates at one, five, twenty-five, fifty, and one hundred percent with seventy-two-hour minimums.

Then the reveal. The commit co-author tags say Claude — but the actual inference was open-weights models routed through Plexus, an API gateway. DeepSeek, Qwen, GLM, Kimi, MiniMax. The tags are an artifact of the client, not the model identity. Every line of implementation — all four hundred and forty-three commits — was done with open models. GPT-5.6 Sol was used exactly once: to design the Vector Cortex master plan. The plan was proprietary. The build was open. A frontier model was the architect. Open models were the builders. A human was the director.