diff --git a/micopay/backend/package.json b/micopay/backend/package.json
index 52e72a7..c9ab772 100644
--- a/micopay/backend/package.json
+++ b/micopay/backend/package.json
@@ -17,7 +17,11 @@
     "test:kyc-didit": "node --import tsx src/tests/kyc-didit.test.ts",
     "test:security": "node --import tsx src/tests/security.test.ts",
     "test:sign-requests": "node --import tsx src/tests/signRequests.test.ts",
-    "issue-device-key": "tsx src/scripts/issue-device-key.ts"
+    "issue-device-key": "tsx src/scripts/issue-device-key.ts",
+    "test:trade-auth": "ALLOW_IN_MEMORY_DB=true MOCK_STELLAR=true SECRET_ENCRYPTION_KEY=0000000000000000000000000000000000000000000000000000000000000000 node --import tsx src/tests/tradeAuth.test.ts",
+    "test:refund": "ALLOW_IN_MEMORY_DB=true MOCK_STELLAR=true SECRET_ENCRYPTION_KEY=0000000000000000000000000000000000000000000000000000000000000000 node --import tsx src/tests/refund.test.ts",
+    "test:challenge": "ALLOW_IN_MEMORY_DB=true MOCK_STELLAR=true SECRET_ENCRYPTION_KEY=0000000000000000000000000000000000000000000000000000000000000000 node --import tsx src/tests/challenge.service.test.ts",
+    "test:discovery": "ALLOW_IN_MEMORY_DB=true MOCK_STELLAR=true SECRET_ENCRYPTION_KEY=0000000000000000000000000000000000000000000000000000000000000000 node --import tsx src/tests/merchant.discovery.test.ts"
   },
   "dependencies": {
     "@fastify/cors": "^8.5.0",
diff --git a/micopay/backend/src/routes/merchants.ts b/micopay/backend/src/routes/merchants.ts
index 20311fc..1d427a3 100644
--- a/micopay/backend/src/routes/merchants.ts
+++ b/micopay/backend/src/routes/merchants.ts
@@ -1,5 +1,6 @@
 import type { FastifyInstance } from 'fastify';
 import { authMiddleware } from '../middleware/auth.middleware.js';
+import { createRateLimiter } from '../middleware/rateLimit.middleware.js';
 import {
   getOrCreateMerchantConfig,
   updateMerchantConfig,
@@ -7,6 +8,12 @@ import {
 } from '../services/merchant.service.js';
 import db from '../db/schema.js';
 
+// G1: /merchants/available is public and unauthenticated — without a rate
+// limit it lets anyone scrape the full census of merchant locations by
+// sweeping lat/lng. 30 req/min per IP is generous for legitimate use (the
+// app makes one request per search).
+const discoveryRateLimit = createRateLimiter({ windowMs: 60_000, max: 30 });
+
 export async function merchantRoutes(app: FastifyInstance) {
   /**
    * GET /merchants/available
@@ -20,6 +27,7 @@ export async function merchantRoutes(app: FastifyInstance) {
    *   flow       – 'cashout' | 'deposit' (optional, reserved)
    */
   app.get('/merchants/available', {
+    preHandler: [discoveryRateLimit],
     schema: {
       querystring: {
         type: 'object',
diff --git a/micopay/backend/src/services/merchant.service.ts b/micopay/backend/src/services/merchant.service.ts
index a50e153..a752e71 100644
--- a/micopay/backend/src/services/merchant.service.ts
+++ b/micopay/backend/src/services/merchant.service.ts
@@ -220,8 +220,13 @@ export async function getAvailableMerchants(
       min_trade_mxn: r.min_trade_mxn,
       max_trade_mxn: r.max_trade_mxn,
       daily_cap_mxn: r.daily_cap_mxn,
-      latitude: parseFloat(r.latitude as unknown as string),
-      longitude: parseFloat(r.longitude as unknown as string),
+      // G1 privacy: coarsen public discovery coordinates to ~110m (3 decimals).
+      // Exact coordinates are only revealed to a counterparty inside an
+      // accepted trade, never at discovery time. distance_km above is
+      // already computed in SQL from the exact, unrounded columns, so it
+      // stays accurate — only these two output fields are rounded.
+      latitude: Math.round(parseFloat(r.latitude as unknown as string) * 1000) / 1000,
+      longitude: Math.round(parseFloat(r.longitude as unknown as string) * 1000) / 1000,
       address_text: r.address_text,
       distance_km: Math.round(distanceKm * 1000) / 1000,
       payout_mxn: payoutMxn,
diff --git a/micopay/backend/src/tests/merchant.discovery.test.ts b/micopay/backend/src/tests/merchant.discovery.test.ts
new file mode 100644
index 0000000..d646e74
--- /dev/null
+++ b/micopay/backend/src/tests/merchant.discovery.test.ts
@@ -0,0 +1,163 @@
+/**
+ * G1 — /merchants/available is public, unauthenticated and (before this fix)
+ * had no rate limit and returned exact lat/lng, letting anyone scrape the
+ * full census of merchant locations.
+ *
+ * This test covers the two mitigations from docs/PLAN_MAPA_REAL_2026-07.md
+ * WP3:
+ *   (a) getAvailableMerchants() rounds the *returned* latitude/longitude to
+ *       3 decimals (~110m) while distance_km keeps its existing precision.
+ *   (b) the discoveryRateLimit limiter (createRateLimiter({ windowMs: 60_000,
+ *       max: 30 })) throws a RateLimitError (429, Retry-After) once a single
+ *       IP exceeds `max` requests inside the window.
+ *
+ * Runs against the in-memory DB (ALLOW_IN_MEMORY_DB=true, no PostgreSQL
+ * needed), following the pattern of tradeAuth.test.ts / refund.test.ts.
+ *
+ * NOTE on (a): the in-memory SQL shim in src/db/schema.ts is a small regex
+ * based mock. It does not evaluate computed SQL columns (the HAVERSINE_SQL
+ * expression aliased as distance_km, or the seller_id/username/trades_*
+ * subqueries), only special-cases LEFT JOIN (not the plain INNER JOIN this
+ * query uses against `users`), and — critically — its WHERE-clause regex
+ * (`/\bWHERE\b.../`) matches the *first* literal "WHERE" in the raw SQL
+ * text, which here is the one inside the nested trades_completed/
+ * trades_terminal subqueries, not the query's real WHERE. Seeding rows into
+ * merchant_configs and calling getAvailableMerchants() end-to-end therefore
+ * can't reliably exercise this query against the mock — it's a limitation of
+ * the mock, not of getAvailableMerchants() itself (against real PostgreSQL
+ * the query runs as written).
+ *
+ * So instead this test stubs `db.getMany` for the duration of the call,
+ * returning exactly the shape PostgreSQL would for one seeded merchant, and
+ * asserts on what getAvailableMerchants() does with that row — i.e. it
+ * targets the actual code under test (the rounding in the .map() in
+ * src/services/merchant.service.ts), independent of the mock SQL engine.
+ */
+
+import { strictEqual, ok, notStrictEqual } from "assert";
+import db from "../db/schema.js";
+import { getAvailableMerchants } from "../services/merchant.service.js";
+import { InMemoryStore, createRateLimiter } from "../middleware/rateLimit.middleware.js";
+import { RateLimitError } from "../utils/errors.js";
+
+// ── (a) coordinate rounding ─────────────────────────────────────────────────
+
+async function testAvailableMerchantsRoundsCoordinates() {
+  const preciseLat = 19.432608123; // exact GPS reading, many decimals
+  const preciseLng = -99.133209456;
+  const preciseDistanceKm = 12.34567; // exact haversine result, as Postgres would compute it
+
+  const originalGetMany = db.getMany;
+  db.getMany = (async (_text: string, _params?: any[]) => [
+    {
+      seller_id: "user-discovery-1",
+      username: "merchant_discovery_1",
+      rate_percent: "1.5",
+      min_trade_mxn: 100,
+      max_trade_mxn: 50000,
+      daily_cap_mxn: 250000,
+      latitude: String(preciseLat),
+      longitude: String(preciseLng),
+      address_text: "CDMX",
+      distance_km: String(preciseDistanceKm),
+      trades_completed: "3",
+      trades_terminal: "3",
+    },
+  ]) as typeof db.getMany;
+
+  let results: Awaited<ReturnType<typeof getAvailableMerchants>>;
+  try {
+    results = await getAvailableMerchants({
+      lat: preciseLat,
+      lng: preciseLng,
+      radius_km: 5,
+      amount_mxn: 500,
+    });
+  } finally {
+    db.getMany = originalGetMany;
+  }
+
+  ok(results.length >= 1, "expected the seeded merchant to be returned");
+  const merchant = results.find((m) => m.address_text === "CDMX");
+  ok(merchant, "expected to find the seeded merchant by address_text");
+
+  const expectedLat = Math.round(preciseLat * 1000) / 1000;
+  const expectedLng = Math.round(preciseLng * 1000) / 1000;
+
+  strictEqual(merchant!.latitude, expectedLat, "latitude must be rounded to 3 decimals");
+  strictEqual(merchant!.longitude, expectedLng, "longitude must be rounded to 3 decimals");
+  notStrictEqual(merchant!.latitude, preciseLat, "rounded latitude must differ from the precise input");
+  notStrictEqual(merchant!.longitude, preciseLng, "rounded longitude must differ from the precise input");
+
+  // decimal-place check: no more than 3 digits after the decimal point
+  const decimalsOf = (n: number) => (String(n).split(".")[1] ?? "").length;
+  ok(decimalsOf(merchant!.latitude) <= 3, "latitude must have at most 3 decimal places");
+  ok(decimalsOf(merchant!.longitude) <= 3, "longitude must have at most 3 decimal places");
+
+  // distance_km keeps its own (already existing) 3-decimal rounding and is
+  // NOT derived from the coarsened lat/lng — it stays independently accurate.
+  strictEqual(
+    merchant!.distance_km,
+    Math.round(preciseDistanceKm * 1000) / 1000,
+    "distance_km must reflect the precise coordinates, unaffected by public lat/lng rounding",
+  );
+
+  console.log("  ✓ getAvailableMerchants() rounds public latitude/longitude to 3 decimals, distance_km unaffected");
+}
+
+// ── (b) discovery rate limiter ─────────────────────────────────────────────
+
+async function testDiscoveryRateLimiterBlocksAfterMax() {
+  const store = new InMemoryStore();
+  const windowMs = 1000;
+  const max = 30;
+
+  // Same construction as the discoveryRateLimit wired into
+  // src/routes/merchants.ts (createRateLimiter({ windowMs: 60_000, max: 30 })),
+  // using a shorter window here so the test doesn't need to wait a full minute.
+  const discoveryRateLimit = createRateLimiter({
+    windowMs,
+    max,
+    store,
+    keyGenerator: (req) => req.ip,
+  });
+
+  const mockReq = { ip: "203.0.113.7" };
+  const mockReply = {
+    header: (_name: string, _value: any) => {},
+  };
+
+  for (let i = 0; i < max; i++) {
+    await (discoveryRateLimit as any)(mockReq, mockReply);
+  }
+  console.log(`  ✓ ${max} requests from the same IP within the window are allowed`);
+
+  let threw = false;
+  try {
+    await (discoveryRateLimit as any)(mockReq, mockReply);
+  } catch (err) {
+    threw = true;
+    ok(err instanceof RateLimitError, `expected RateLimitError, got ${(err as Error)?.constructor?.name}`);
+    strictEqual((err as RateLimitError).statusCode, 429, "rate-limited response must be 429");
+    ok((err as RateLimitError).retryAfter !== undefined, "rate-limited response must carry retryAfter");
+  }
+  ok(threw, `request ${max + 1} should have thrown RateLimitError`);
+  console.log("  ✓ request past max is rejected with 429 and Retry-After");
+
+  // A different IP is unaffected by the first IP's exhausted budget.
+  const otherReq = { ip: "203.0.113.99" };
+  await (discoveryRateLimit as any)(otherReq, mockReply);
+  console.log("  ✓ a different IP is not affected by another IP's rate limit");
+}
+
+async function main() {
+  console.log("\nMerchant discovery privacy & rate-limit tests\n");
+  await testAvailableMerchantsRoundsCoordinates();
+  await testDiscoveryRateLimiterBlocksAfterMax();
+  console.log("\nAll merchant.discovery tests passed.\n");
+}
+
+main().catch((err) => {
+  console.error("❌ merchant.discovery tests failed:", err);
+  process.exit(1);
+});