This series hardens MV shutdown behavior by fixing lifecycle tracking for detached view-builder callbacks and aligning update handling with the same async dispatch style used by create/drop.
Patch 1 refactors on_update_view to use a dedicated coroutine dispatcher (dispatch_update_view), keeping update logic serialized under the existing view-builder lock and consistent with the callback architecture already used for create/drop paths.
Patch 2 adds explicit callback lifetime coordination in view_builder:
- introduce a seastar::gate member
- acquire _ops_gate.hold() when launching detached create/update/drop dispatch futures
- keep the hold alive until each detached future resolves
- close the gate during view_builder::drain() so shutdown waits for in-flight callback work before final teardown
Together, these changes reduce shutdown race exposure in MV event handling while preserving existing behavior for normal operation.
Testing:
- pytest --test-py-init test/cluster/mv (47 passed, 7 skipped)
backport: not required started happening in master
fixes: SCYLLADB-687
Closesscylladb/scylladb#28648
* github.com:scylladb/scylladb:
db/view: gate detached view-builder callbacks during shutdown
db:view: refactor on_update_view to use coroutine dispatcher
a4c389413c