W2: async job infra + researcher sub-agent

- src/store/jobs.ts: per-job JSON store in data/jobs (create/get/update/list,
  dedup by toolCallId)
- src/agent/tools/jobs.ts: research tool — client-side (no execute), turn ends
  at the call; input per contracts ResearchToolInput
- src/agent/tools/web.ts: server-side web_search (Google CSE) + web_fetch
  (Readability/Turndown/linkedom, Jina fallback) — errors return as strings,
  never thrown into the agent loop. Deps: @mozilla/readability, linkedom,
  turndown (+@types/turndown dev)
- src/agent/subagents/researcher.ts: isolated ToolLoopAgent (web tools only,
  12-step cap), researcher prompt ported from pi
- src/agent/subagents/runner.ts: spawnPendingJobs hook + runResearchJob —
  fire-and-forget, activity line per tool call, fulfills the part in the
  LATEST chat record (output-available) before flipping job status; failure
  still fulfills the part so the teacher learns the outcome
- src/server/chat-handler.ts: onFinish spawn hook after saveMessages
- app/api/jobs/route.ts: GET ?chatId= polling endpoint
- components/artifacts/job-card.tsx + registry entry: polling activity card
  (2s) → syncFromServer on finish; research-brief card (markdown + sources)
- src/agent/prompts/20-jobs.md: research doctrine for the teacher
- tests/jobs.test.ts: store CRUD, spawn hook via scripted mock teacher,
  runner completion/failure with fake model + stubbed fetch

app/api/jobs/route.ts

@@ -0,0 +1,18 @@
+import { listJobs } from "@/src/store/jobs";
+
+/**
+ * Job status polling endpoint (contracts.ts "THE ASYNC PROTOCOL" §4): the
+ * client polls GET /api/jobs?chatId=… while any job tool part is pending,
+ * finds the job by toolCallId, renders its activity line, and re-syncs the
+ * chat when the job flips to done/error.
+ */
+export async function GET(req: Request) {
+	const chatId = new URL(req.url).searchParams.get("chatId");
+	if (!chatId) {
+		return Response.json({ error: "chatId query parameter is required" }, { status: 400 });
+	}
+	if (!/^[A-Za-z0-9_-]+$/.test(chatId)) {
+		return Response.json({ error: "Invalid chatId" }, { status: 400 });
+	}
+	return Response.json({ jobs: listJobs(chatId) });
+}