feat(wave2): add @mosaic/openclaw-context plugin to monorepo

- OpenClaw → OpenBrain context engine plugin migrated from mosaic/openclaw-openbrain-context
- Depends on @mosaic/types workspace:*
- Typecheck passing

plugins/openclaw-context/openclaw.plugin.json

@@ -0,0 +1,58 @@
+{
+  "id": "openclaw-openbrain-context",
+  "name": "OpenBrain Context Engine",
+  "description": "OpenBrain-backed ContextEngine plugin for OpenClaw",
+  "version": "0.0.1",
+  "kind": "context-engine",
+  "configSchema": {
+    "type": "object",
+    "additionalProperties": false,
+    "required": ["baseUrl", "apiKey"],
+    "properties": {
+      "baseUrl": {
+        "type": "string",
+        "minLength": 1,
+        "description": "Base URL of your OpenBrain REST API"
+      },
+      "apiKey": {
+        "type": "string",
+        "minLength": 1,
+        "description": "Bearer token used to authenticate against OpenBrain"
+      },
+      "source": {
+        "type": "string",
+        "minLength": 1,
+        "default": "openclaw",
+        "description": "Source prefix stored in OpenBrain (session id is appended)"
+      },
+      "recentMessages": {
+        "type": "integer",
+        "minimum": 1,
+        "default": 20,
+        "description": "How many recent thoughts to fetch during assemble/bootstrap"
+      },
+      "semanticSearchLimit": {
+        "type": "integer",
+        "minimum": 1,
+        "default": 10,
+        "description": "How many semantic matches to request during assemble"
+      },
+      "subagentRecentMessages": {
+        "type": "integer",
+        "minimum": 1,
+        "default": 8,
+        "description": "How many thoughts to use when seeding/summarizing subagents"
+      }
+    }
+  },
+  "uiHints": {
+    "baseUrl": {
+      "label": "OpenBrain Base URL",
+      "placeholder": "https://brain.example.com"
+    },
+    "apiKey": {
+      "label": "OpenBrain API Key",
+      "sensitive": true
+    }
+  }
+}