diff --git a/cloud/src/Repository/AuditRepository.php b/cloud/src/Repository/AuditRepository.php
new file mode 100644
index 0000000..5f3a18a
--- /dev/null
+++ b/cloud/src/Repository/AuditRepository.php
@@ -0,0 +1,8 @@
+<?php
+declare(strict_types=1);
+namespace App\Repository;
+
+interface AuditRepository
+{
+    public function append(string $actor, string $action, string $target, array $before, array $after): void;
+}
diff --git a/cloud/src/Repository/DeviceRepository.php b/cloud/src/Repository/DeviceRepository.php
new file mode 100644
index 0000000..5b5a06e
--- /dev/null
+++ b/cloud/src/Repository/DeviceRepository.php
@@ -0,0 +1,10 @@
+<?php
+declare(strict_types=1);
+namespace App\Repository;
+
+interface DeviceRepository
+{
+    public function secretFor(string $deviceId): ?string;
+    public function touchHeartbeat(string $deviceId, array $meta): void;
+    public function configVersion(string $deviceId): int;
+}
diff --git a/cloud/src/Repository/EventRepository.php b/cloud/src/Repository/EventRepository.php
new file mode 100644
index 0000000..237d4ba
--- /dev/null
+++ b/cloud/src/Repository/EventRepository.php
@@ -0,0 +1,11 @@
+<?php
+declare(strict_types=1);
+namespace App\Repository;
+
+interface EventRepository
+{
+    public function insert(array $event): int;
+    public function recent(int $limit, ?string $severity): array;
+    public function find(int $id): ?array;
+    public function acknowledge(int $id, string $user): bool;
+}
diff --git a/cloud/src/Repository/NonceRepository.php b/cloud/src/Repository/NonceRepository.php
new file mode 100644
index 0000000..7a418fa
--- /dev/null
+++ b/cloud/src/Repository/NonceRepository.php
@@ -0,0 +1,9 @@
+<?php
+declare(strict_types=1);
+namespace App\Repository;
+
+interface NonceRepository
+{
+    public function seen(string $nonce): bool;
+    public function remember(string $nonce, int $expiresAt): void;
+}
diff --git a/cloud/src/Repository/RateLimiterRepository.php b/cloud/src/Repository/RateLimiterRepository.php
new file mode 100644
index 0000000..59f090c
--- /dev/null
+++ b/cloud/src/Repository/RateLimiterRepository.php
@@ -0,0 +1,9 @@
+<?php
+declare(strict_types=1);
+namespace App\Repository;
+
+interface RateLimiterRepository
+{
+    /** 해당 window(분)의 key 카운트를 1 증가시키고, 증가 후 카운트를 반환한다. */
+    public function hit(string $key, int $windowStart): int;
+}
diff --git a/cloud/src/Repository/SnapshotRepository.php b/cloud/src/Repository/SnapshotRepository.php
new file mode 100644
index 0000000..0cf5fa3
--- /dev/null
+++ b/cloud/src/Repository/SnapshotRepository.php
@@ -0,0 +1,10 @@
+<?php
+declare(strict_types=1);
+namespace App\Repository;
+
+interface SnapshotRepository
+{
+    public function add(int $eventId, string $fileUuid, string $contentHash): void;
+    public function forEvent(int $eventId): array;
+    public function pathByUuid(string $uuid): ?string;
+}
diff --git a/cloud/src/Repository/ThresholdRepository.php b/cloud/src/Repository/ThresholdRepository.php
new file mode 100644
index 0000000..9acb517
--- /dev/null
+++ b/cloud/src/Repository/ThresholdRepository.php
@@ -0,0 +1,8 @@
+<?php
+declare(strict_types=1);
+namespace App\Repository;
+
+interface ThresholdRepository
+{
+    public function forDevice(string $deviceId): array;
+}
diff --git a/cloud/src/Repository/UserRepository.php b/cloud/src/Repository/UserRepository.php
new file mode 100644
index 0000000..2c00acc
--- /dev/null
+++ b/cloud/src/Repository/UserRepository.php
@@ -0,0 +1,10 @@
+<?php
+declare(strict_types=1);
+namespace App\Repository;
+
+interface UserRepository
+{
+    public function byUsername(string $username): ?array;
+    public function recordFailure(int $userId, int $lockUntil): void;
+    public function clearFailures(int $userId): void;
+}
diff --git a/cloud/src/Repository/ZoneRepository.php b/cloud/src/Repository/ZoneRepository.php
new file mode 100644
index 0000000..a392c86
--- /dev/null
+++ b/cloud/src/Repository/ZoneRepository.php
@@ -0,0 +1,11 @@
+<?php
+declare(strict_types=1);
+namespace App\Repository;
+
+interface ZoneRepository
+{
+    public function forDevice(string $deviceId): array;
+    public function forCamera(string $cameraId): array;
+    public function save(array $zone): string;
+    public function delete(string $zoneId): bool;
+}
diff --git a/cloud/tests/RepositoryContractTest.php b/cloud/tests/RepositoryContractTest.php
new file mode 100644
index 0000000..d9975c1
--- /dev/null
+++ b/cloud/tests/RepositoryContractTest.php
@@ -0,0 +1,32 @@
+<?php
+declare(strict_types=1);
+namespace App\Tests;
+require_once __DIR__ . '/Support/InMemoryRepositories.php';
+use App\Tests\Support\{InMemoryNonceRepository, InMemoryEventRepository, InMemoryRateLimiter};
+use PHPUnit\Framework\TestCase;
+
+final class RepositoryContractTest extends TestCase
+{
+    public function testNonceRememberThenSeen(): void
+    {
+        $r = new InMemoryNonceRepository();
+        $this->assertFalse($r->seen('n1'));
+        $r->remember('n1', 999);
+        $this->assertTrue($r->seen('n1'));
+    }
+    public function testEventInsertAndRecent(): void
+    {
+        $r = new InMemoryEventRepository();
+        $id = $r->insert(['severity' => 'high', 'event_type' => 'fall']);
+        $this->assertSame(1, $id);
+        $this->assertCount(1, $r->recent(10, null));
+        $this->assertCount(0, $r->recent(10, 'critical'));
+    }
+    public function testRateLimiterIncrements(): void
+    {
+        $r = new InMemoryRateLimiter();
+        $this->assertSame(1, $r->hit('dev', 100));
+        $this->assertSame(2, $r->hit('dev', 100));
+        $this->assertSame(1, $r->hit('dev', 160));
+    }
+}
diff --git a/cloud/tests/Support/InMemoryRepositories.php b/cloud/tests/Support/InMemoryRepositories.php
new file mode 100644
index 0000000..669e16d
--- /dev/null
+++ b/cloud/tests/Support/InMemoryRepositories.php
@@ -0,0 +1,61 @@
+<?php
+declare(strict_types=1);
+namespace App\Tests\Support;
+use App\Repository\{DeviceRepository, NonceRepository, RateLimiterRepository,
+    EventRepository, SnapshotRepository, UserRepository, ZoneRepository,
+    ThresholdRepository, AuditRepository};
+
+final class InMemoryDeviceRepository implements DeviceRepository {
+    public array $heartbeats = [];
+    public function __construct(private array $secrets = [], private array $versions = []) {}
+    public function secretFor(string $d): ?string { return $this->secrets[$d] ?? null; }
+    public function touchHeartbeat(string $d, array $m): void { $this->heartbeats[$d] = $m; }
+    public function configVersion(string $d): int { return $this->versions[$d] ?? 1; }
+}
+final class InMemoryNonceRepository implements NonceRepository {
+    public array $store = [];
+    public function seen(string $n): bool { return isset($this->store[$n]); }
+    public function remember(string $n, int $exp): void { $this->store[$n] = $exp; }
+}
+final class InMemoryRateLimiter implements RateLimiterRepository {
+    public array $counts = [];
+    public function hit(string $k, int $w): int { $key = "$k:$w"; return $this->counts[$key] = ($this->counts[$key] ?? 0) + 1; }
+}
+final class InMemoryEventRepository implements EventRepository {
+    public array $rows = []; private int $seq = 0;
+    public function insert(array $e): int { $id = ++$this->seq; $this->rows[$id] = $e + ['event_id' => $id, 'acknowledged_by' => null]; return $id; }
+    public function recent(int $limit, ?string $sev): array {
+        $r = array_reverse($this->rows, true);
+        if ($sev !== null) $r = array_filter($r, fn($x) => $x['severity'] === $sev);
+        return array_slice(array_values($r), 0, $limit);
+    }
+    public function find(int $id): ?array { return $this->rows[$id] ?? null; }
+    public function acknowledge(int $id, string $u): bool { if (!isset($this->rows[$id])) return false; $this->rows[$id]['acknowledged_by'] = $u; return true; }
+}
+final class InMemorySnapshotRepository implements SnapshotRepository {
+    public array $rows = []; public array $paths = [];
+    public function add(int $e, string $uuid, string $hash): void { $this->rows[$e][] = ['file_uuid' => $uuid, 'content_hash' => $hash]; $this->paths[$uuid] = "/tmp/$uuid.jpg"; }
+    public function forEvent(int $e): array { return $this->rows[$e] ?? []; }
+    public function pathByUuid(string $u): ?string { return $this->paths[$u] ?? null; }
+}
+final class InMemoryUserRepository implements UserRepository {
+    public function __construct(public array $users = []) {}
+    public function byUsername(string $u): ?array { return $this->users[$u] ?? null; }
+    public function recordFailure(int $id, int $lock): void { foreach ($this->users as &$row) if ($row['id'] === $id) { $row['failed_attempts'] = ($row['failed_attempts'] ?? 0) + 1; $row['locked_until'] = $lock; } }
+    public function clearFailures(int $id): void { foreach ($this->users as &$row) if ($row['id'] === $id) { $row['failed_attempts'] = 0; $row['locked_until'] = 0; } }
+}
+final class InMemoryZoneRepository implements ZoneRepository {
+    public array $zones = []; private int $seq = 0;
+    public function forDevice(string $d): array { return array_values(array_filter($this->zones, fn($z) => ($z['device_id'] ?? '') === $d)); }
+    public function forCamera(string $c): array { return array_values(array_filter($this->zones, fn($z) => $z['camera_id'] === $c)); }
+    public function save(array $z): string { $id = $z['zone_id'] ?? ('z' . (++$this->seq)); $this->zones[$id] = $z + ['zone_id' => $id]; return $id; }
+    public function delete(string $id): bool { if (!isset($this->zones[$id])) return false; unset($this->zones[$id]); return true; }
+}
+final class InMemoryThresholdRepository implements ThresholdRepository {
+    public function __construct(private array $data = []) {}
+    public function forDevice(string $d): array { return $this->data[$d] ?? []; }
+}
+final class InMemoryAuditRepository implements AuditRepository {
+    public array $log = [];
+    public function append(string $a, string $act, string $t, array $b, array $af): void { $this->log[] = compact('a', 'act', 't', 'b', 'af'); }
+}