RFC 0015: host.kvStorage capability

Summary

Adds an optional host.kvStorage capability — a TTL-aware key-value store with atomic increment + compare-and-swap primitives. Required by core.openwop.storage's kv-\* nodes. The Make-Data-Store equivalent for openwop.

Motivation

Workflows need cross-run state. Today every pack invents its own external store (Redis client, Postgres table, S3 prefix), each with a different cross-tenant isolation bug. A single capability with a single SECURITY invariant for cross-tenant isolation is the leverage point.

Proposal

§A Capability schema addition

{
  "kvStorage": {
    "type": "object",
    "description": "Key-value store with TTL + atomic ops. Per-tenant isolation enforced by the host.",
    "properties": {
      "supported": { "type": "boolean" },
      "maxKeyBytes": { "type": "integer", "minimum": 0 },
      "maxValueBytes": { "type": "integer", "minimum": 0 },
      "maxTtlSeconds": { "type": "integer", "minimum": 0 },
      "atomicIncrement": { "type": "boolean" },
      "compareAndSwap": { "type": "boolean" }
    },
    "additionalProperties": false
  }
}

§B Host-contract MUSTs

A host advertising kvStorage.supported: true MUST:

1. Partition values by tenant. A get for one tenant MUST NOT return values from another tenant, even with identical keys. 2. Enforce maxKeyBytes and maxValueBytes advertised values. 3. Honor TTL with at most a 1-second drift on expiry visibility. 4. If atomicIncrement: true is advertised, increments MUST be atomic across concurrent callers. 5. If compareAndSwap: true is advertised, CAS MUST be atomic (no read-modify-write races).

§C SECURITY invariant

- id: kv-cross-tenant-isolation
  tier: protocol
  summary: "host.kvStorage MUST partition values by tenant. Cross-tenant reads MUST return not-found."
  conformance_test: "kv-cross-tenant-isolation.test.ts"

Mirrors the existing agentMemoryCrossTenantIsolation invariant.

§D Conformance

• kv-cross-tenant-isolation.test.ts: set under tenant A, get under tenant B → not found.
• kv-atomic-increment.test.ts: 1000 concurrent +1s → final value is 1000.
• kv-cas.test.ts: stale expect rejected.
• kv-ttl-expiry.test.ts: TTL honored within 1s drift.

Compatibility

Additive. Optional capability; core.openwop.storage kv-\* nodes refuse registration on hosts that don't advertise it.

Implementation notes (non-normative)

• Schema diff in §A lands in schemas/capabilities.schema.json on Active promotion, not at Draft.
• SECURITY invariant kv-cross-tenant-isolation lands in SECURITY/invariants.yaml alongside the matching scenario; mirrors the existing agent-memory-cti-1 pattern.
• Reference impl candidate: in-memory Map per tenant in examples/hosts/in-memory/.

Acceptance criteria

• [x] Capability block.
• [x] host-capabilities.md §host.kvStorage section. (Landed at commit c5831fe.)
• [x] Invariant + 4 scenarios.
• [x] In-memory reference host implementation.
• [x] CHANGELOG entry.

References

• Make Data Store (prior art).
• agentMemoryCrossTenantIsolation (existing isolation pattern).
• core.openwop.storage pack.