Two rounds of agent-handoff dogfood testing surfaced that Smriti had no
way to delete spaces, sessions, or checkpoints via any surface. This
adds DELETE endpoints to the V2/V4 API, new CLI commands, and UI
affordances on the workspace overview and chat history panel so the
daily cleanup path does not require opening a Python shell.
Checkpoint delete refuses with 409 Conflict when child commits or
forked sessions reference the target, because silently orphaning them
would cause walk_ancestors to collapse lineage and forked sessions to
lose isolation. The refusal is escaped via ?cascade=true on the API,
--cascade on the CLI, and a two-step confirm with a dependents list
plus checkbox in the UI modal.
Space delete relies on the existing DB-level cascade chain from the
earlier commit/session/turn migrations — no new Alembic migration is
needed. Session delete cascades turn events but preserves commits
authored by the session, since commits are space-owned artifacts.
14 integration tests cover cascade correctness, 409 refusal, the
cascade escape hatch, cross-user 404s, subtree ordering, and
idempotency. Existing tests pass unchanged (143/143).
