After an AI-written document is closed, its session_id is nulled (the detach
behaviour from #1238). Both Open controls in the Documents library — the card's
expanded Open button and the card dropdown's Open item — gated on
`doc.session_id`: they wired `libraryOpenInSession` (which early-returns with no
session) and DISABLED the control otherwise, so the user's own document showed a
grayed-out Open button and couldn't be reopened.
The module already has `libraryOpenDocument`, which explicitly handles the
orphaned case ("just open in editor without switching session" -> _loadDocument
by id). Route the no-session path there instead of disabling.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
