[gustav-fff]

Closes #746

Root cause

AuxFinderPool.acquire() pushes into entries only after waitForScan() resolves (packages/pi-fff/src/aux-finders.ts:84), so two concurrent acquire("/Users/<user>") both observe empty entries and each spawn a separate full-home scan — no dedup, unlike the main finder's finderPromise. Separately, picker.grep() (packages/pi-fff/src/index.ts:708) was called with no timeBudgetMs; the native call is synchronous so an AbortSignal cannot interrupt an in-flight search, and the fuzzy fallback repeated the full traversal after an exhausted exact pass.

Fix

Coalesce in-flight AuxFinderPool creations by root through a pending map so concurrent acquires share one finder/scan. Pass a finite GREP_TIME_BUDGET_MS (10s) to both native grep calls (engine returns partial results + nextCursor on timeout). Skip the automatic fuzzy fallback when the exact pass left a nextCursor (corpus not exhausted), avoiding a repeated broad-root walk.

Steps to reproduce

On pre-fix origin/main:

cd packages/pi-fff
cat > test/repro.test.ts <<'TS'
import { describe, expect, mock, test } from "bun:test";
const created: any[] = [];
const mod = { FileFinder: { create: (o: any) => {
  const f = { isDestroyed: false, basePath: o.basePath,
    waitForScan: () => new Promise((r) => setTimeout(r, 50)),
    destroy() { f.isDestroyed = true; } };
  created.push(f); return { ok: true, value: f };
} } };
mock.module("@ff-labs/fff-node", () => mod);
mock.module("@ff-labs/fff-bun", () => mod);
const { AuxFinderPool } = await import("../src/aux-finders");
describe("#746", () => { test("dedup", async () => {
  const pool = new AuxFinderPool({ enableFsRootScanning: false });
  const [a, b] = await Promise.all([pool.acquire("/Users/x"), pool.acquire("/Users/x")]);
  expect(created.length).toBe(1);
  expect(a.finder).toBe(b.finder);
}); });
TS
bun test test/repro.test.ts

Expected: created.length === 1, one shared finder.
Actual (pre-fix):

Expected: 1
Received: 2
(fail) #746 > dedup

Two separate finders created for the same root → two concurrent full-home scans, matching the reported tens-of-minutes hang.

How verified

cd packages/pi-fff && bun test test/
# 47 pass, 0 fail (includes new test/aux-dedup.test.ts covering the race)

The regression test two concurrent acquires for same root share one finder fails on pre-fix main and passes with this change.

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