diff --git a/apps/web/lib/__tests__/participantsExport.test.ts b/apps/web/lib/__tests__/participantsExport.test.ts
new file mode 100644
index 000000000..186c1fe8e
--- /dev/null
+++ b/apps/web/lib/__tests__/participantsExport.test.ts
@@ -0,0 +1,96 @@
+// Tests for streaming participants CSV export (#1184).
+
+import {
+  csvEscape,
+  participantToCsvLine,
+  streamParticipantsCsv,
+  collectParticipantRows,
+} from "../participantsExport";
+
+describe("participants CSV export (#1184)", () => {
+  test("csvEscape quotes fields containing commas, quotes, newlines", () => {
+    expect(csvEscape("plain")).toBe("plain");
+    expect(csvEscape("with,comma")).toBe('"with,comma"');
+    expect(csvEscape('has "quote"')).toBe('"has ""quote"""');
+    expect(csvEscape("multi\nline")).toBe('"multi\nline"');
+  });
+
+  test("participantToCsvLine emits ordered columns", () => {
+    const line = participantToCsvLine({
+      rank: 1,
+      wallet: "GABC",
+      alias: "alice",
+      score: 42,
+      completionTime: "2026-08-24T00:00:00.000Z",
+      joinedAt: "2026-08-23T00:00:00.000Z",
+    });
+    expect(line).toBe("1,GABC,alice,42,2026-08-24T00:00:00.000Z,2026-08-23T00:00:00.000Z");
+  });
+
+  test("streamParticipantsCsv streams header then chunks lazily", async () => {
+    const total = 250;
+    const calls: Array<[number, number]> = [];
+    const rowSource = async (offset: number, limit: number) => {
+      calls.push([offset, limit]);
+      const rows = [];
+      for (let i = offset; i < Math.min(offset + limit, total); i++) {
+        rows.push({
+          rank: i + 1,
+          wallet: `W${i}`,
+          alias: "",
+          score: 100 - i,
+          completionTime: "2026-08-24T00:00:00.000Z",
+          joinedAt: "2026-08-20T00:00:00.000Z",
+        });
+      }
+      return rows;
+    };
+
+    const stream = streamParticipantsCsv(total, 100, rowSource);
+    const reader = (stream as ReadableStream<Uint8Array>).getReader();
+    const decoder = new TextDecoder();
+
+    let text = "";
+    let chunkCount = 0;
+    while (true) {
+      const { done, value } = await reader.read();
+      if (done) break;
+      text += decoder.decode(value);
+      chunkCount += 1;
+    }
+
+    // header + 3 data chunks (250 rows / 100 per chunk)
+    expect(chunkCount).toBe(4);
+    const lines = text.trim().split("\n");
+    expect(lines[0]).toBe("rank,wallet,alias,score,completion_time,joined_at");
+    expect(lines).toHaveLength(total + 1);
+    expect(calls).toEqual([
+      [0, 100],
+      [100, 100],
+      [200, 100],
+    ]);
+  });
+
+  test("collectParticipantRows excludes privacy opt-outs from ranking", async () => {
+    const leaderboard = [
+      { address: "W1", points: 30 },
+      { address: "W2", points: 20 },
+      { address: "W3", points: 10 },
+    ];
+    const participants = [
+      { address: "W1", alias: "alice", points: 30, privacy: { shareResults: true } },
+      { address: "W2", alias: "bob", points: 20, privacy: { shareResults: false } },
+      { address: "W3", alias: "", points: 10 },
+    ];
+
+    const rows = await collectParticipantRows(
+      leaderboard,
+      [],
+      async () => participants,
+    );
+
+    // W2 opted out -> excluded entirely; W3 gets rank 2 (not 3)
+    expect(rows.map((r) => r.wallet)).toEqual(["W1", "W3"]);
+    expect(rows[1].rank).toBe(2);
+  });
+});
diff --git a/apps/web/lib/participantsExport.ts b/apps/web/lib/participantsExport.ts
new file mode 100644
index 000000000..22efe89c5
--- /dev/null
+++ b/apps/web/lib/participantsExport.ts
@@ -0,0 +1,138 @@
+// Streaming CSV export of hunt participants and results (#1184).
+//
+// Mirrors the leaderboard export route but adds:
+//  - participant rows (not just leaderboard ranks), honoring privacy settings
+//  - streaming via ReadableStream so large exports don't buffer in memory
+//
+// Privacy: participants who set `shareResults: false` are excluded from the
+// export entirely; their row never leaves the server.
+
+// Pure module: data sources are injected by the caller (route), so this
+// file has no server-only imports and stays unit-testable in isolation.
+
+export interface ParticipantRow {
+  rank: number;
+  wallet: string;
+  alias: string | "";
+  score: number;
+  completionTime: string;
+  joinedAt: string;
+}
+
+export interface ExportPrivacyOptions {
+  /** When false, the participant is excluded from exports (their choice). */
+  shareResults?: boolean;
+}
+
+export function csvEscape(value: string | number): string {
+  const s = String(value);
+  if (/[",\n\r]/.test(s)) {
+    return `"${s.replace(/"/g, '""')}"`;
+  }
+  return s;
+}
+
+/** Yield-safe CSV header for the participants export. */
+export function participantsCsvHeader(): string {
+  return "rank,wallet,alias,score,completion_time,joined_at";
+}
+
+/** Serialize one participant row as a CSV line. */
+export function participantToCsvLine(row: ParticipantRow): string {
+  return [
+    csvEscape(row.rank),
+    csvEscape(row.wallet),
+    csvEscape(row.alias),
+    csvEscape(row.score),
+    csvEscape(row.completionTime),
+    csvEscape(row.joinedAt),
+  ].join(",");
+}
+
+/**
+ * Build a streaming web ReadableStream of CSV text from participant rows.
+ * Rows are pulled lazily through `rowSource` in chunks so very large hunts
+ * do not need to fit in memory.
+ */
+export function streamParticipantsCsv(
+  total: number,
+  chunkSize: number,
+  rowSource: (offset: number, limit: number) => Promise<ParticipantRow[]>,
+): ReadableStream<Uint8Array> {
+  const encoder = new TextEncoder();
+  let offset = 0;
+  let headerSent = false;
+
+  return new ReadableStream<Uint8Array>({
+    async pull(controller) {
+      if (!headerSent) {
+        controller.enqueue(encoder.encode(participantsCsvHeader() + "\n"));
+        headerSent = true;
+        return;
+      }
+      if (offset >= total) {
+        controller.close();
+        return;
+      }
+      const rows = await rowSource(offset, chunkSize);
+      if (rows.length === 0) {
+        controller.close();
+        return;
+      }
+      const text = rows.map(participantToCsvLine).join("\n") + "\n";
+      controller.enqueue(encoder.encode(text));
+      offset += rows.length;
+    },
+  });
+}
+
+/**
+ * Collect participant rows for a hunt, applying privacy filtering.
+ * Participants with shareResults === false are excluded before any row is built.
+ */
+export async function collectParticipantRows(
+  leaderboard: Array<{ address: string; points: number }>,
+  fastest: Array<{ address?: string; completionTimeSeconds?: number }>,
+  getParticipants: () => Promise<
+    Array<{
+      address: string;
+      alias?: string;
+      points?: number;
+      completedAt?: number;
+      joinedAt?: number;
+      privacy?: ExportPrivacyOptions;
+    }>
+  >,
+): Promise<ParticipantRow[]> {
+
+  const completionTimeByWallet = new Map<string, number>();
+  for (const entry of fastest) {
+    if (entry.address && typeof entry.completionTimeSeconds === "number") {
+      completionTimeByWallet.set(entry.address, entry.completionTimeSeconds * 1000);
+    }
+  }
+
+  const participants = await getParticipants();
+  const sorted = [...leaderboard].sort((a, b) => b.points - a.points);
+
+  const rows: ParticipantRow[] = [];
+  let rank = 0;
+  for (const entry of sorted) {
+    const participant = participants.find((p) => p.address === entry.address);
+    // Privacy: exclude participants who opted out of sharing results.
+    if (participant?.privacy?.shareResults === false) continue;
+    rank += 1;
+    const completionMs =
+      completionTimeByWallet.get(entry.address) ??
+      (participant?.completedAt ?? Date.now());
+    rows.push({
+      rank,
+      wallet: entry.address,
+      alias: participant?.alias ?? "",
+      score: entry.points,
+      completionTime: new Date(completionMs).toISOString(),
+      joinedAt: new Date(participant?.joinedAt ?? completionMs).toISOString(),
+    });
+  }
+  return rows;
+}
diff --git a/apps/web/vitest.no-setup.config.ts b/apps/web/vitest.no-setup.config.ts
new file mode 100644
index 000000000..0282691aa
--- /dev/null
+++ b/apps/web/vitest.no-setup.config.ts
@@ -0,0 +1,22 @@
+import react from "@vitejs/plugin-react";
+import path from "path";
+import { defineConfig } from "vitest/config";
+
+// Minimal config for pure-logic tests (#1194): no jsdom setup file, so the
+// pre-existing react/react-dom version mismatch in the repo does not block
+// tests that do not touch React.
+
+export default defineConfig({
+  plugins: [react()],
+  oxc: {
+    jsx: {
+      runtime: "automatic",
+    },
+  },
+  test: {
+    environment: "node",
+    globals: true,
+    setupFiles: [],
+    exclude: ["e2e/**", "node_modules/**"],
+  },
+});