v1: OpenAI-compat alias + smart provider routing — gateway is now drop-in middleware

/v1/chat/completions route alias (same handler as /chat) lets any tool
using the official `openai` SDK adopt the gateway via OPENAI_BASE_URL
alone — no custom provider field needed.

resolve_provider() extended:
- bare `vendor/model` (slash) → openrouter (catches x-ai/grok-4.1-fast,
  moonshotai/kimi-k2, deepseek/deepseek-v4-flash, openai/gpt-oss-120b:free)
- bare vendor model names (no slash, no colon) get auto-prefixed:
  gpt-* / o1-* / o3-* / o4-* → openai/<name>  (OpenRouter form)
  claude-* → anthropic/<name>
  grok-* → x-ai/<name>
  Then routed to openrouter. Ollama models (with colon, no slash) keep
  default routing. Tools like pi-ai validate against an OpenAI-style
  catalog and send bare names — this lets them flow through cleanly.

Verified end-to-end:
- curl POST /v1/chat/completions {model: "gpt-4o-mini", ...} → 200,
  routed to openrouter as openai/gpt-4o-mini
- openai SDK with baseURL=http://localhost:3100/v1 → 3 model variants all
  succeed (openai/gpt-4o-mini, gpt-4o-mini, x-ai/grok-4.1-fast)
- Langfuse traces fire automatically on every call
  (v1.chat:openrouter, provider tagged in metadata)

scripts/mode_pass5_variance_paid.ts gains LH_CONDITIONS env so subset
runs (e.g. just isolation vs composed) take half the latency.

Archon-on-Lakehouse integration: gateway side is done. Pi-ai's
openai-responses backend uses /v1/responses (not /chat/completions) and
its openrouter backend appears to bail in client-side validation before
sending. Patching Pi locally to override baseUrl works for arch but the
harness still rejects — needs more work in a follow-up. Direct openai
SDK path (langchain-js / agents / patched Pi) works today.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/mode_pass5_variance_paid.ts

@@ -34,13 +34,22 @@ interface Condition {
   corpus?: string | string[];
 }
 
-const CONDITIONS: Condition[] = [
+const ALL_CONDITIONS: Condition[] = [
   { label: "isolation       ",  mode: "codereview_isolation"  },
   { label: "arch_only       ",  mode: "codereview_lakehouse",  corpus: "lakehouse_arch_v1" },
   { label: "symbols_only    ",  mode: "codereview_lakehouse",  corpus: "lakehouse_symbols_v1" },
   { label: "composed (A+C)  ",  mode: "codereview_lakehouse"  /* uses modes.toml default */ },
 ];
 
+// Optional whitelist via env: LH_CONDITIONS=isolation,composed limits the
+// run to a subset (matches against the trimmed `label`). Useful when only
+// the head-to-head pair matters and saves ~50% latency on slow rungs.
+const wantedLabels = (process.env.LH_CONDITIONS ?? "")
+  .split(",").map(s => s.trim().toLowerCase()).filter(Boolean);
+const CONDITIONS: Condition[] = wantedLabels.length === 0
+  ? ALL_CONDITIONS
+  : ALL_CONDITIONS.filter(c => wantedLabels.some(w => c.label.trim().toLowerCase().startsWith(w)));
+
 async function runOne(c: Condition, rep: number): Promise<{ ok: boolean; latency_ms?: number; resp_chars?: number; error?: string }> {
   const body: any = {
     task_class: "scrum_review",