docs: context engine

docs/concepts/context.md

@@ -153,6 +153,12 @@ What persists across messages depends on the mechanism:
 
 Docs: [Session](/concepts/session), [Compaction](/concepts/compaction), [Session pruning](/concepts/session-pruning).
 
+By default, OpenClaw uses the built-in `legacy` context engine for assembly and
+compaction. If you install a plugin that provides `kind: "context-engine"` and
+select it with `plugins.slots.contextEngine`, OpenClaw delegates context
+assembly, `/compact`, and related subagent context lifecycle hooks to that
+engine instead.
+
 ## What `/context` actually reports
 
 `/context` prefers the latest **run-built** system prompt report when available:

docs/plugins/manifest.md

@@ -66,6 +66,10 @@ Optional keys:
 - The manifest is **required for all plugins**, including local filesystem loads.
 - Runtime still loads the plugin module separately; the manifest is only for
   discovery + validation.
+- Exclusive plugin kinds are selected through `plugins.slots.*`.
+  - `kind: "memory"` is selected by `plugins.slots.memory`.
+  - `kind: "context-engine"` is selected by `plugins.slots.contextEngine`
+    (default: built-in `legacy`).
 - If your plugin depends on native modules, document the build steps and any
   package-manager allowlist requirements (for example, pnpm `allow-build-scripts`
   - `pnpm rebuild <package>`).

docs/tools/plugin.md

@@ -66,6 +66,7 @@ Plugins can register:
 - Agent tools
 - CLI commands
 - Background services
+- Context engines
 - Optional config validation
 - **Skills** (by listing `skills` directories in the plugin manifest)
 - **Auto-reply commands** (execute without invoking the AI agent)
@@ -370,6 +371,7 @@ Fields:
 - `allow`: allowlist (optional)
 - `deny`: denylist (optional; deny wins)
 - `load.paths`: extra plugin files/dirs
+- `slots`: exclusive slot selectors such as `memory` and `contextEngine`
 - `entries.<id>`: per‑plugin toggles + config
 
 Config changes **require a gateway restart**.