fix(dashboard): persist session close metadata on empty message windows (#4501)

[md-abusayeed]

Problem / Motivation

Closing a dashboard chat session that contains no messages (e.g. newly created at birth or created programmatically) fails to persist the \closed: true\ and \closed_at\ metadata flags to disk. Consequently, when the gateway restarts, rehydration restores the empty session back into the sidebar despite the user having closed it.

Why it matters

In _save_slot_to_history\ (\src/kiro_crew/dashboard/chat_persistence.py), the function began with an unqualified \if not window: return\ guard. This guard sat directly above the no-op check whose documentation explicitly states that \closed, \orce, and
ewrite\ must always proceed to disk.

Because \if not window: return\ was evaluated first without checking \closed, closing an empty slot resulted in an early return without writing the updated metadata line containing \closed\ and \closed_at. The caller (\�pi_chat_slot_delete\ via \save_slot_off_loop(..., closed=True, closed_at=closed_at)) treated the operation as successful, but on-disk metadata remained unclosed.

What changed

• Updated the empty-window early-return guard in _save_slot_to_history\ to \if not window and not closed: return.
• Added defensive \getattr(state, 'conversation_log', None)\ and safe int checks for resumed count.
• Plain background saves on empty slots remain cheap no-ops as intended.
• Explicit session close (\closed=True) on empty message windows now proceeds into the metadata lock and writes the updated metadata line to disk atomically.

Tests

• Added \ est/test_chat_persistence_empty_slot.py:
  • \ est_closing_empty_slot_persists_closed_metadata: Asserts that closing an empty slot persists \closed: true\ and \closed_at\ to the session JSONL file on disk.
  • \ est_plain_save_on_empty_slot_is_noop: Asserts that plain periodic saves on empty slots remain no-ops and write no files.
• Ran pytest suite: 2/2 tests pass (\pytest test/test_chat_persistence_empty_slot.py).

Manual verification

N/A — unit coverage sufficient: direct unit tests assert on-disk metadata existence and contents via \ConversationLog.get_metadata.

Screenshots / video

Why no screenshot: backend persistence and session lifecycle fix — no visual UI change.

Related Issues

Closes #4501

Checklist

• Single commit with a Conventional Commits title (\eat|fix|docs|refactor|perf|test|chore|ci|build|revert: ...)
• Existing tests pass and new tests added for new functionality
• Self-review completed; code follows project style guidelines
• Documentation updated (if applicable) — N/A, behavior documented in code comments
• No secrets, credentials, or internal references in the diff