feat(sendbox): persist per-conversation drafts across app restarts

[baanish]

What problem does it solve?

AionUi already preserves each conversation's composer draft while the app is running, but the current useSendBoxDraft store is memory-only. Restarting, updating, or crashing the app discards long unsent prompts, which is especially painful for multi-step coding instructions.

Proposed solution

Persist the existing per-conversation draft model behind useSendBoxDraft using a small, versioned renderer-side persistence adapter.

• Hydrate saved drafts when a conversation's send box mounts, without overwriting a newer in-memory edit.
• Debounce writes so typing does not cause a storage write on every keystroke.
• Keep drafts isolated by conversation ID and agent type (ACP / Codex / AionRS), matching the current store.
• Clear a draft after a successful send and when its conversation is deleted.
• Ignore malformed or stale persisted data safely.
• Persist text and workspace mention paths; do not persist file bytes or transient in-progress uploads. Missing paths should be dropped during restore.
• Add focused tests for restart hydration, conversation isolation, clear-on-send, and corrupt-data recovery.

The storage mechanism can use the existing client-settings path if that is the preferred project convention; otherwise a renderer-local versioned store keeps this change self-contained.

Scope

Renderer send-box draft handling and the successful-send/conversation-cleanup paths. No model-provider or AionCore behavior changes are required.

Willing to implement it yourself?

Yes. If accepted and converted to a bonus issue, I will implement it, add tests, and provide before/after verification.

[github-actions[bot]]

Thanks for posting! @IceyLiu will take a look soon. / 感谢发帖！@IceyLiu 会尽快跟进。