[1/4] Multi-hop query: skeleton E2E

[zipdoki]

Skeleton E2E for design alignment of the wide-row EdgeCache model (Phase 0 of #214).

This PR introduces the EdgeCache wide-row design and validates it end-to-end with mocks, covering metadata creation → data insertion → multi-hop query.

Step 1: Metadata Creation

Add caches field to edge schema — defines cache name, sort fields, and row limit.

"caches": [
  {
    "cache": "recent_wishlist",
    "fields": [{"field": "createdAt", "order": "DESC"}],
    "limit": 100
  }
]

Step 2: Data Insertion

Introduce EdgeCacheRecord as a wide-row model — row key encodes source/table/direction/cache, qualifier holds sort values + target, value holds version + properties.

[EdgeCache - Wide Row]
Row       : hash(source) | tableCode | EDGE_CACHE(-6) | OUT | cacheCode
Qualifier : cacheValues + target
Value     : version + properties

Step 3: Multi-hop Query

Wire CACHE step type into ActionbaseQuery — resolves source references from previous hops and scans the EdgeCache row.

curl -X POST http://localhost:8080/graph/v3/query \
  -H "Content-Type: application/json" \
  -d '{
    "query": [
      {
        "type": "SCAN",
        "name": "hop1",
        "service": "social",
        "label": "follows",
        "src": {"type": "VALUE", "value": ["user1"]},
        "dir": "OUT",
        "index": "created_at_desc",
        "limit": 100,
        "include": false
      },
      {
        "type": "CACHE",
        "name": "hop2",
        "service": "commerce",
        "label": "wishlist",
        "src": {"type": "REF", "ref": "hop1", "field": "tgt"},
        "dir": "OUT",
        "cacheName": "recent_wishlist",
        "limit": 10,
        "include": true
      }
    ]
  }'

EdgeCache Query Endpoint

Add a REST endpoint for single-key EdgeCache lookup.

curl -X GET "http://localhost:8080/graph/v3/databases/{database}/tables/{table}/edges/cache/{cache}?start={source}&direction=OUT&limit=10"

How to test

./gradlew :server:test --tests "*.ActionbaseQueryCacheE2ETest"
./gradlew :engine:test --tests "*.ActionbaseQueryParserSpec"
./gradlew :core:test --tests "*.EdgeSchemaSerializationTest"
./gradlew :core:test --tests "*.TableSerializationTest"

[em3s]

Looks necessary, but feels out of scope here. Let’s track this separately.

[em3s]

Same as above. Out of scope

[em3s]

Same as above. Out of scope

[em3s]

Same as above. Out of scope

[em3s]

The tests ActionbaseQueryParserSpec.kt and ActionbaseQueryCacheE2ETest.kt are well written. Any changes not required to run these tests are out of scope for this PR.

Suggestions:

1. Remove out-of-scope changes not required to run the two tests.
2. Add a dedicated /graph/v3/databases/{database}/tables/{table}/edges/cache endpoint alongside get, scan, count, and agg, with tests.
3. Migrate ActionbaseQuery to v3 as a separate PR before this one, then update the tests to use it.

[em3s]

I'd like to rename the cache/{cache} endpoint. Here are the candidates:

• lookup/{cache} — looking up a pre-built wide row structure
• seek/{cache} — pairs well with scan, same low-level DB terminology
• hop/{cache} — reflects its role in multi-hop graph traversal
• walk/{cache} — walking the graph step by step

Which do you prefer?

[zipdoki]

@em3s
I prefer seek/{cache} — consistent with existing DB terminology, and jumping directly to a row key aligns well with EdgeCache wide-row lookups. What do you think?

[zipdoki]

@em3s
Addressed your feedback — thanks for the review!

1. Removed out-of-scope changes. ✅
2. Added the /edges/cache/{cache} endpoint with tests. ✅
3. Opened Migrate ActionbaseQuery to v3 service layer #218 as a separate PR.