fix(cache): preserve empty nested JSON objects (DAT-2310)

[abnegate]

What changed

• preserve empty JSON objects as stdClass while retaining associative arrays for non-empty objects
• use the fidelity-preserving decoder in Redis, Redis Cluster, Hazelcast, and Redis multiplexing envelope reads and touches
• cover root, nested, and list empty objects separately from empty arrays

Seen red

On current main, the new Redis envelope regression returned empty arrays in place of every empty object:

• expected: {"empty":{},"nested":{"empty":{}},"list":[{},...],"emptyArray":[]}
• actual: {"empty":[],"nested":{"empty":[]},"list":[[],...],"emptyArray":[]}

Verification

• cache unit suite: 102 tests, 217 assertions, 4 existing capability skips
• JSON fidelity E2E: Redis, Sharding, Hazelcast: 3 tests, 12 assertions
• Redis Cluster fidelity E2E on a native arm64 six-node Redis 7 cluster: 1 test, 4 assertions
• Redis multiplexing fidelity E2E: 1 test, 4 assertions
• non-cluster, non-multiplexing E2E: 61 tests, 181 assertions
• bin/monorepo check cache
• bin/monorepo validate

The repository Redis Cluster image is amd64-only and its healthcheck segfaults under local arm64 emulation, so the exact fidelity case was also run against a native six-node Redis 7 cluster. The complete local multiplexing E2E process still hits an unrelated existing Swoole segmentation fault; the new multiplexing regression itself passes independently.

Release chain

This is the cache layer of DAT-2310. A stable cache 4.0.x release is required before database, server-ce, and Cloud lock updates; no temporary VCS pin is introduced.

Related: utopia-php/mongo#48, #123.

[greptile-apps]

Greptile Summary

The PR preserves empty JSON objects as stdClass while continuing to decode non-empty objects as associative arrays.

• Adds a shared fidelity-preserving JSON decoder.
• Integrates it into Redis envelopes, Redis Cluster, and Hazelcast load/touch paths.
• Adds unit and E2E coverage for root, nested, and list-contained empty objects while distinguishing empty arrays.

Confidence Score: 5/5

The PR appears safe to merge, with no actionable correctness or security failures identified.

The new decoder preserves only the intended empty-object distinction, continues converting valid envelopes and non-empty JSON objects to associative arrays, forwards decoding flags, and retains existing malformed-envelope behavior across each integrated adapter.

Important Files Changed

Filename	Overview
packages/cache/src/Cache/Adapter/Json.php	Adds recursive JSON conversion that retains empty objects while preserving the adapters’ existing associative-array representation for non-empty objects.
packages/cache/src/Cache/Adapter/Redis/Envelope.php	Routes Redis envelope reads and touches through the fidelity-preserving decoder without changing validation, expiration, or malformed-input behavior.
packages/cache/src/Cache/Adapter/RedisCluster.php	Applies fidelity-preserving decoding to Redis Cluster load and touch operations while retaining existing envelope checks.
packages/cache/src/Cache/Adapter/Hazelcast.php	Applies the shared decoder to Hazelcast load and touch paths so nested empty objects survive round trips.
packages/cache/tests/Cache/Scope/EmptyObjectFidelity.php	Provides reusable E2E coverage for empty objects at multiple nesting positions, empty arrays, and touch behavior.
packages/cache/tests/Cache/Unit/RedisEnvelopeTest.php	Adds focused regression coverage confirming empty-object fidelity across Redis envelope decode and touch operations.

_{Reviews (1): Last reviewed commit: "(fix): preserve empty objects in JSON-ba..." | Re-trigger Greptile}