> ## Documentation Index
> Fetch the complete documentation index at: https://docs2.openclaw.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Plugin SDK memory and context slots

The registrars that allow only one active implementation at a time, and the
memory adapter contracts that sit on top of them. Part of the
[Plugin SDK overview](/plugins/sdk-overview).

## Exclusive slots

| Method                                     | What it registers                                                                                                                                                                                                        |
| ------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `api.registerContextEngine(id, factory)`   | Context engine (one active at a time). Use `info.acceptedHostParams` to restrict accepted host-added lifecycle fields, including optional `maintain()` cancellation; undeclared engines receive all current host fields. |
| `api.registerMemoryCapability(capability)` | Unified memory capability                                                                                                                                                                                                |

To participate in durable admitted turns, context engines must declare
`currentTurnFence: "before-current-turn-entry-v1"` and
`turnAdvancementIdempotency: "atomic-idempotent-v1"` under
`info.transcriptSemantics`, then implement `commitTurn(...)` as an atomic,
idempotent write keyed by `advancementKey`. OpenClaw supplies only the inclusive
accepted turn, from its admitted user entry through its terminal entry; use the
`readSessionTranscriptVisibleMessageDelta(...)` cursor API to bootstrap or
rebuild earlier history. Without the full contract, OpenClaw uses the legacy
context path for the whole logical turn and its retries, leaves the configured
engine unchanged, and tries that engine again on the next logical turn.

## Memory embedding adapters

* `registerMemoryCapability` is the exclusive memory-plugin API.
* `registerMemoryCapability` may also expose `publicArtifacts.listArtifacts(...)`
  for host-managed exports. Companion plugins that enumerate those declared
  artifacts still use `listActiveMemoryPublicArtifacts(...)` from the retained
  `openclaw/plugin-sdk/memory-host-core` facade until a focused public consumer
  API exists; they must not reach into another plugin's private layout.
* A memory runtime that can return session-transcript hits should implement
  `runtime.authorizeSearchHits(...)`. The host calls this hook before raw search
  hits reach caller-visible surfaces and supplies the requesting agent, session
  key, and sandbox state. Return only hits the requester may observe. If the hook
  is absent, OpenClaw fails closed by withholding session-source hits while
  retaining ordinary memory hits. Keep transcript identity and visibility
  policy in the owning memory plugin; callers must not infer authorization from
  paths or duplicate plugin-specific rules.
* `MemoryFlushPlan.model` can pin the flush turn to an exact `provider/model`
  reference, such as `ollama/qwen3:8b`, without inheriting the active fallback
  chain.
* Embedding providers use `api.registerEmbeddingProvider(...)` and
  `contracts.embeddingProviders`; there is no separate memory-only registry.