[Bug] A plugin appending user/message without message.id permanently bricks the session history

[jilian-dsh]

Summary A single malformed user/message event (missing message.id) can permanently block an entire session's history from loading: the session fails with SessionPersistenceCorruptionError ... session event at seq N lacks an identified message. We hit this in a real session (508k events; one bad event at seq 440160).

Root cause — write/load validation asymmetry

Write path: Agent.followup() → send() → inbox.splice() (packages/core/agent-loop) performs no validation of message.id; session.append only checks JSON-serializability. A user/message without id is silently persisted.
Load path: Session.fromRestore() → assertMessageEventShape() (packages/core/session) strictly requires a non-empty message.id. Because the bad event sits inside an already-committed prefix, the whole session refuses to load; the only recovery is manual log surgery.
Reproduction

Any plugin registers a command whose handler calls agent.followup({ role: "user", content: [...], source: { kind: "user" } }) without an id (easy in plain JS — the UserMessage type is not enforced at runtime).
Run the command in a session.
Restart DSH and reopen the session → "history unavailable … lacks an identified message".
Suggested fixes

Validate message.id on the write path (in Agent.followup/send, or in session.append for message events), matching the load-time invariant — turn silent data corruption into a loud, early error.
Optionally, make the load path resilient: skip/quarantine a single malformed message event with a warning instead of refusing the whole log.
Workaround for plugin authors: always build messages with createUserMessage() (from @deepseek-ai/dsh-llm) or include id: crypto.randomUUID().

Environment: DSH 0.1.0-rc.6 (npm), Windows, web profile.

中文摘要：发现 DSH 写入/加载校验不对称的 bug——agent.followup 和 session.append 对消息 id 零校验，而加载历史时严格校验 message.id 非空。插件构造消息漏写 id 会让坏事件落盘，最终锁死整个会话历史（实测：50.8 万事件中仅 1 条坏事件即可导致全部历史无法加载）。建议：① 写入路径补校验（与加载对齐）；② 加载路径对单条坏事件容错。插件作者应使用官方 createUserMessage()（自动生成 id）。