golangLAKEHOUSE/reports/cutover/g5_first_slice_live.md

G5 cutover slice live — first real Bun-frontend traffic to Go substrate

2026-05-01: the Bun mcp-server (which serves devop.live/lakehouse/ via nginx → :3700) now has a /_go/* pass-through that routes requests to the Go gateway. Real frontend traffic can flow through the Go substrate while the existing /api/* path (Rust gateway) stays untouched.

What changed

Rust legacy repo (/home/profit/lakehouse/):

• mcp-server/index.ts:
  • New GO_BASE = process.env.GO_LAKEHOUSE_URL || "" (off-by-default)
  • New /_go/* handler at the same shape as /api/* (forwarded method+headers+body) but pointing at ${GO_BASE}${path}
  • Returns 503 with rationale when GO_LAKEHOUSE_URL is unset
  • Returns 502 when Go gateway is unreachable (preserves operator visibility into Go-side failures vs silent fallback)

System config:

• /etc/systemd/system/lakehouse-agent.service.d/go-cutover.conf:

  [Service]
  Environment=GO_LAKEHOUSE_URL=http://127.0.0.1:4110
  

  Drop-in adds the env var to the systemd-managed Bun service. Reversible via systemctl revert lakehouse-agent.service or by removing the file.

Go rewrite repo (this commit): documentation + cross-runtime parity log entry.

Verification (all live, against persistent Go stack on :4110)

Path	Routes to	Verdict
GET /_go/health	Go gateway :4110/health	{"status":"ok","service":"gateway"}
POST /_go/v1/embed	Go embedd via gateway	nomic-embed-text-v2-moe vectors, dim=768
POST /_go/v1/matrix/search	Go matrixd via gateway	3/3 Forklift Operators against the 200-worker persistent corpus
GET /api/health (control)	Rust gateway :3100/health	lakehouse ok (unchanged)

Search results from the live cutover slice:

rank=0 id=w-43  dist=0.445 Brian Ramirez   (Forklift Operator, Springfield, IL)
rank=1 id=w-102 dist=0.448 Laura Long      (Forklift Operator, Cleveland,   OH)
rank=2 id=w-101 dist=0.485 Terrence Gray   (Forklift Operator, Champaign,   IL)

3/3 role match. Top-1 in IL exactly. Real coordinator-shape query served by Go substrate via Bun frontend.

What this is

This is the first time real Bun-frontend traffic has reached the Go substrate end-to-end. Production paths (devop.live/lakehouse/* → nginx → Bun :3700 → /api/) still go through Rust on :3100; the new /_go/ path is a parallel slice that operators or external tools can hit to validate Go under realistic frontend conditions.

The cutover unit is FULLY ADDITIVE:

• No existing tool modified
• /api/* unchanged
• All Bun mcp-server tools that currently call BASE (Rust) unchanged
• /_go/* fails-closed (503) when env var unset

The cutover unit is FULLY REVERSIBLE:

• Unset GO_LAKEHOUSE_URL → /_go/* returns 503
• systemctl revert lakehouse-agent → removes the drop-in
• git revert of the Bun source change → removes the handler

What this is NOT

• Not an nginx flip. devop.live/lakehouse/* still goes through Rust. Operators have to opt into /_go/*.
• Not a wholesale routing change. Each path under /_go/ is a manual choice; no automatic routing of Rust paths to Go equivalents.
• Not a transformation layer. /_go/v1/embed expects the Go request shape ({texts, model}); /_go/* doesn't translate Rust-shaped requests for the caller.

Operational discipline

The systemd drop-in is at /etc/systemd/system/lakehouse-agent.service.d/. Operators inspecting the system should know to look there for cutover-related env overrides.

The persistent Go stack must be up at :4110 for /_go/* to succeed. Tear down via pkill -f 'bin/persistent-'. Bring up via scripts/cutover/start_go_stack.sh.

What's next

• Pick a real coordinator-facing tool to flip. The current /_go/* pass-through is operator-facing (manual curl). The next step would be modifying ONE specific tool in mcp-server/index.ts (e.g. /search → /v1/matrix/search) to optionally route through Go when GO_BASE is set, with response shape adapter. That's a product-visible flip; current state is infrastructure-visible.
• Shadow-read mode. A hybrid where /api/* ALSO calls /_go/* in parallel and logs diffs to stderr — operators see Go-vs-Rust divergences on real traffic without changing user-facing behavior. Cleaner cutover discipline than direct flip.
• Production load test. This slice has been exercised on 3 manual curl requests. A traffic generator hitting /_go/v1/matrix/search at sustained rate would expose latency / stability under load that single-shot tests can't.