feat: analysis pipeline with staged SSE

Adds @openuidev/lang-core (one-line reason: the prompt-side library must build in a non-React Node runtime; react-lang's createContext crashes the route's server bundle).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/analyst.ts

@@ -1,5 +1,6 @@
 import { z } from "zod/v4";
 import { digestForModel, type Digest } from "./digest.ts";
+import { openAiTextDeltas } from "./stream.ts";
 import type { AnalystConfig } from "./settings.ts";
 
 export class AnalystError extends Error {}
@@ -36,11 +37,11 @@ export function extractJson(text: string): unknown {
 }
 
 export async function proposeCandidates(cfg: AnalystConfig, digest: Digest, note: string,
-    fetchImpl: typeof fetch = fetch): Promise<Candidate[]> {
+    fetchImpl: typeof fetch = fetch, signal?: AbortSignal): Promise<Candidate[]> {
   const res = await fetchImpl(`${cfg.baseUrl}/chat/completions`, {
-    method: "POST",
+    method: "POST", signal,
     headers: { "content-type": "application/json", authorization: `Bearer ${cfg.apiKey}` },
-    body: JSON.stringify({ model: cfg.model, temperature: 0.6, ...cfg.extra, stream: false,
+    body: JSON.stringify({ model: cfg.model, temperature: 0.6, max_tokens: 2048, ...cfg.extra, stream: false,
       messages: [{ role: "system", content: CANDIDATE_SYSTEM_PROMPT },
         { role: "user", content: JSON.stringify({ digest: digestForModel(digest), user_note: note || null }) }] }),
   }).catch((e) => { throw new AnalystError(`Could not reach ${cfg.baseUrl}: ${(e as Error).message}`); });
@@ -56,3 +57,23 @@ export async function proposeCandidates(cfg: AnalystConfig, digest: Digest, note
   }
   return parsed.data.candidates;
 }
+
+export const REPORT_SYSTEM_PROMPT = (openuiPrompt: string) => `${openuiPrompt}
+
+You are writing the final answer for a DBA holding one SQL Server execution plan. The ranking you are given was
+computed by Jev from typed judgments. It is not your opinion: do not re-rank it, soften it, or hide it. Quote each
+option's scores as given. A rewrite must return the same rows as the original — when in doubt keep the original text
+and say why. Never invent a number that is not in the input.`;
+
+export async function* streamReport(cfg: AnalystConfig, payload: unknown, openuiPrompt: string,
+    fetchImpl: typeof fetch = fetch, signal?: AbortSignal): AsyncGenerator<string> {
+  const res = await fetchImpl(`${cfg.baseUrl}/chat/completions`, {
+    method: "POST", signal,
+    headers: { "content-type": "application/json", authorization: `Bearer ${cfg.apiKey}` },
+    body: JSON.stringify({ model: cfg.model, temperature: 0.3, max_tokens: 2048, ...cfg.extra, stream: true,
+      messages: [{ role: "system", content: REPORT_SYSTEM_PROMPT(openuiPrompt) },
+        { role: "user", content: JSON.stringify(payload) }] }),
+  }).catch((e) => { throw new AnalystError(`Could not reach ${cfg.baseUrl}: ${(e as Error).message}`); });
+  if (!res.ok || !res.body) throw new AnalystError(`Analyst model returned HTTP ${res.status} while writing the report.`);
+  yield* openAiTextDeltas(res);
+}