Phase 5.5-5.9: Plugin-Marketplace, Agent Memory, GraphRAG, Subagents, External Agent API

5.5 Plugin-Marketplace:
- New plugin: marketplace/ (models, routes, services, schemas, config)
- MarketplaceListing model (global, no tenant_id)
- Ed25519 signature verification via PluginSignature
- Endpoints: list, detail, install, verify, categories
- Config: MARKETPLACE_SERVER_URL setting

5.6 Agent Memory (persistent):
- New plugin: agent_memory/ (models, routes, services, schemas)
- AgentMemory model with embedding vector(768) + HNSW index
- store_memory() with auto-embedding
- retrieve_relevant_memories() with pgvector cosine similarity
- Semantic search endpoint

5.7 GraphRAG:
- New plugin: graph_rag/ (models, routes, services, provider, schemas)
- EntityRelationship model (source/target type+id, relationship_type, metadata)
- BFS graph traversal (bidirectional, configurable depth)
- GraphRAGSearchProvider registered in unified_search

5.8 Subagents / Multi-Agent:
- AgentCoordinator class (create_subtask, wait_for_subtask, aggregate, cancel)
- AgentSubtask model + migration 0002_agent_subtasks.sql
- 6 new API endpoints for subtask management
- Tools registered in AI tool registry

5.9 External Agent API:
- external_api.py: POST /run, GET /status, POST /stream (SSE)
- Bearer API token authentication
- Rate limiting: 10 req/min per token
- ExternalAgentRequest/Response schemas

3 new plugins registered in main.py and __init__.py
All files py_compile clean

app/plugins/builtins/automation/schemas.py

@@ -289,3 +289,42 @@ class AutomationVersionListResponse(BaseModel):
 
     items: list[AutomationVersionResponse]
     total: int
+
+
+# ─── Subtask Schemas (Phase 5.8) ───
+
+
+class SubtaskCreate(BaseModel):
+    """Create a new subtask for multi-agent orchestration."""
+
+    parent_agent_id: str = Field(..., description="UUID of the parent agent")
+    child_agent_id: str = Field(..., description="UUID of the child agent that will execute")
+    task_description: str = Field(..., min_length=1, description="Description of the task")
+
+
+class SubtaskUpdate(BaseModel):
+    """Update a subtask (status, result)."""
+
+    status: str | None = Field(None, pattern="^(pending|running|completed|failed|cancelled)$")
+    result: dict[str, Any] | None = None
+
+
+class SubtaskRead(BaseModel):
+    """Subtask response."""
+
+    id: str
+    parent_agent_id: str
+    child_agent_id: str
+    task_description: str
+    status: str = "pending"
+    result: dict[str, Any] = {}
+    created_at: str | None = None
+    completed_at: str | None = None
+    updated_at: str | None = None
+
+
+class SubtaskListResponse(BaseModel):
+    """Paginated subtask list."""
+
+    items: list[SubtaskRead]
+    total: int