Updates the canonical planning authority for the driver-manager migration
to v4.3, which closes the last open v4.0 P3 item ('Driver-level
Driver::on_error IPC') via a three-layer architecture:
1. Manager-side trait: DriverConfig::on_error override returns the
severity mapping by default; consultable from the AER dispatch.
2. Sidecar IPC (manager): UnixStream::pair(), child fd as
REDBEAR_DRIVER_ERROR_FD env var, parent fd registered by BDF,
200ms timeout on the IPC roundtrip, fall-back chain (IPC -> in-
process -> severity default).
3. Sidecar IPC (driver): linux-kpi pci_register_error_handler() +
worker thread that services the sidecar fd.
Documents the wire protocol, the C-side API contract, the
discriminant mappings, and the explicit decision to keep wire types
duplicated between driver-manager and linux-kpi rather than extract
a shared crate.
Status table: Open items now empty of v4.0 P3 list items. Remaining
operator-only gates (hardware validation matrix, two-week soak) are
noted but are out of scope for code work. Driver-level Driver::on_error
adoption by shipped drivers is now possible (the IPC layer is ready)
but no daemon opts in yet -- that is an integration task for future
driver work.
Last reviewed line updated to 2026-07-24 (v4.3).
vasilito
bba923e075