[Question] Harness + RemoteFilesystemSpec: session jsonl written to local workspace only, not mirrored to BaseStore — multi-replica deployment concern

## Background

We are building a **server-hosted, multi-tenant Agent platform** (Spring Boot + AG-UI + CopilotKit), **not** a personal/laptop Harness setup.

- **Runtime**: Spring Boot service (`/agui/run`), intended for **K8s multi-replica** deployment.
- **Tenancy**: many logged-in users; `RuntimeContext.userId` injected from **server-side auth** (not client-trusted).
- **Why RemoteFilesystemSpec + DistributedStore**: by design for **shared MySQL** (`agentscope_sessions` + `agentscope_store`) and Redis-backed HTTP sessions — **not** because we want `./data/agentscope-workspace` on pod disk as source of truth.
- **Ephemeral pod disk**: `workspace-dir` (including `.index/workspace.db` and session `*.jsonl`) lives on **container/local server disk**. In production we cannot rely on per-pod PVC as the primary session archive; we expect Harness offload/mirror to **BaseStore** as documented for [Filesystem mode 1 (RemoteFilesystemSpec)](https://java.agentscope.io/v1/zh/docs/harness/filesystem.html).

We integrate **HarnessAgent + DistributedStore (MySQL `JdbcStore` + `MysqlAgentStateStore`) + AG-UI Spring Boot starter + CopilotKit** for this server-side deployment.

Configuration (simplified):

```yaml
agentscope:
harness:
workspace-dir: ./data/agentscope-workspace
storage:
session-table: agentscope_sessions
workspace-table: agentscope_store
agui:
server-side-memory: false
```

```java
HarnessAgent.builder()
.agentId("platform_assistant")
.name("Platform Assistant") // display name differs from agentId
.distributedStore(distributedStore)
.filesystem(new RemoteFilesystemSpec().isolationScope(IsolationScope.USER))
...
```

## What works (MySQL)

- **AgentState / conversation context** → `agentscope_sessions` (`session_id = userId:threadId`) ✅
- **MEMORY.md / memory/YYYY-MM-DD.md** → `agentscope_store` (Remote KV) ✅

**App-layer workaround (server UI)**: we expose custom REST (`/api/chat/threads`, messages from `AgentStateStore`) because AG-UI does not hydrate CopilotKit from persisted store when `server-side-memory: false`.

## Problem: session offload files stay on local disk

After AG-UI conversations, we see session files under **local workspace on the server** (not end-user machines):

```
{workspace}/{userId}/agents/Platform Assistant/sessions/{threadId}.jsonl
{workspace}/{userId}/agents/Platform Assistant/sessions/{threadId}.log.jsonl
```

But **no corresponding entries** appear in `agentscope_store` for `agents/platform_assistant/sessions/`.

From code reading:

1. `SessionTree` always **appends to local files first**, then async mirror to `AbstractFilesystem` (see javadoc: "local file is the working copy").
2. `MemoryFlushMiddleware` uses `agent.getName()` (e.g. `Platform Assistant`) for offload paths, while `RemoteFilesystemSpec` routes `agents/{agentId}/sessions/` with `agentId = platform_assistant`.
3. Path mismatch may cause mirror to hit **LocalFilesystem** layer instead of **RemoteFilesystem → BaseStore**.

## Impact (server-side / multi-replica)

- **Multi-replica / K8s**: each pod has its own `data/agentscope-workspace`; session jsonl is not shared across replicas.
- **CopilotKit / AG-UI UI history**: no `MESSAGES_SNAPSHOT` from persisted store; we work around via `agentscope_sessions`, but jsonl archive gap remains for tools/audit.
- **session_search tool**: may not find history written on another pod.
- **Contradicts mode-1 intent**: we chose RemoteFilesystemSpec specifically for server deployment; local-only jsonl undermines that contract.

## Questions

1. **Is local session jsonl intended as mandatory working copy** even when `RemoteFilesystemSpec` + `DistributedStore` are configured? Or should offload go **directly to BaseStore** in distributed/server mode?
2. **Should middleware use stable `agentId` (from `HarnessAgent.builder().agentId(...)`) instead of `agent.getName()`** for session paths, to match `RemoteFilesystemSpec` routes?
3. **Recommended pattern for server multi-replica**:
- shared PVC for `workspace-dir`?
- or emit AG-UI `MESSAGES_SNAPSHOT` from `AgentStateStore` on `/agui/run`?
- or rely only on `agentscope_sessions.context` and treat jsonl as optional archive?
4. Any plan to integrate **AG-UI `MESSAGES_SNAPSHOT`** with Harness `AgentStateStore` for thread history hydration?

## Environment

- agentscope-java: 2.0.0-local (main)
- Spring Boot 3.4.x, AG-UI starter, HarnessAgent, MySQL store
- AG-UI `server-side-memory: false` (avoid in-memory `ThreadSessionManager` for multi-replica)
- Deployment target: **server-side Agent platform** (not personal desktop)

Related: #2014 (userId injection for AG-UI + Harness)

Thank you!
```