Federated learning staleness bugs

[ale18V]

Summary

This tracking issue groups confirmed defects in federated stale-contribution recovery and aggregation membership handling.

Reproduction branch

The characterization suite is available on federated-learning-staleness-bugs, in server/tests/e2e/federated_stale_reproduction.spec.ts.

Run it from the repository root:

node_modules/.bin/vitest run --project=server server/tests/e2e/federated_stale_reproduction.spec.ts

The suite is a prototype that characterizes current behavior. It intentionally lives only on the reproduction branch and is not proposed for merge into main.

Sub-issues

The sub-issues below track the stale-recovery round number, disconnected-contributor aggregation, and first-round recovery behavior.