fix: keep consecutive requests running and clear finished stop state

Wait for OpenCode session cancellation before reusing a conversation, and replace the session after unconfirmed cancellation. Preserve terminal message state when stale streaming snapshots arrive so finished conversations return to Send.

Validated with full production Electron UI and the configured real text model: queued requests complete, cancellation followed by immediate resend completes, and Stop clears. Focused tests: 362 passed; typecheck and targeted lint passed. Live dispatch counting limitations are recorded in the feature evidence.

Release note: Consecutive OpenCode requests no longer inherit a previous cancellation, and finished conversations no longer retain the Stop button after stale updates.

docs/features/assistant-workbar/runtime-process-reuse-technical-design.md

@@ -159,6 +159,10 @@ SelectedRuntimeManager
 
 会话绑定记录规范化绝对目录及原生 sessionId。同一 conversation 的请求继续串行，
 不同 conversation 并行，不引入覆盖整个 Server 的 Prompt 队列。
+取消或失败时，每次请求只发送一次会话级 abort，并在该调用结束后才释放会话锁，避免
+迟到的 abort 中断下一条请求。abort 使用既有控制请求超时；失败或超时后移除对应绑定，
+下一条请求创建新 Session。这也适用于配置外部 OpenCode HTTP Server 的路径；托管 SSH
+使用独立的 ACP 取消路径。
 现有 `snapshot: false` 必须保留。
 
 `mcpMutationTail` 目前属于 Runtime 对象；共享后同一原生目录的变更必须由同一 owner