P2.1: Add attach_command to TaskStatusView (multiplexer Phase 2)

[takemo101]

Phase 2, issue P2.1 — part of the multiplexer backend abstraction implementation plan.

Design: docs/designs/cuekit-multiplexer-backend-design.md

Prerequisites: Phase 1 (#402, #403, #404) all merged.

Outcome

Every TaskStatusView carries a new attach_command: { argv: string[] } | null field alongside the existing attach_hint: string field. Both are populated by deriving attach_hint from attach_command's argv.

Files

• Modify: packages/core/src/task-status-view.ts
• Modify: packages/adapters/src/pane-adapter.ts

Steps

• Add attach_command to the TaskStatusView schema (Zod) — optional { argv: string[] } or null.
• In the status-view builder in pane-adapter.ts, populate attach_command from backend.attachCommand(handle).
• Compute attach_hint as attach_command?.argv.join(" ") ?? null for backward compatibility.
• Snapshot test: assert both fields present and consistent.

Acceptance

Status views show both attach_hint (existing string) and attach_command (new structured); they agree.