Replace Probe with Agent across node runtime, Fleet contracts, backend state, API and storage. Report incoming sessions and outgoing link health through each Agent uplink, and retain directed link controls and retry.
Update protocol fixtures and end-to-end coverage for the unified model; accept requested cancellation during the Fleet timeout test cleanup.
Registering a manifest with the panel is best effort in CI (an unreachable
panel only warns, the pipeline stays green). The Backend update notice then
never appeared, because the host updater only reads the mailbox the panel
writes. A background poller now fetches the signed manifests of the agent, the
probe and the backend itself from the registry every five minutes, verifies the
release signature and registers them, writing the backend one into the host
updater's mailbox.