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* Add /profiler/consensus_lag to measure apply lag between peers Raft commit index advances on a peer whose apply loop is stalled, so the existing signals - `raft_info.commit` and the `all_nodes_have_same_commit` test helper - report a stuck peer as healthy. Nothing exposes how long a peer has been behind at *applying* entries, which is what shard transfer's `await_consensus_sync` barrier actually waits on. Each peer now keeps a ring of the last 32 entries it applied, stamped with its own wall clock and the time that entry took to apply. The ring is in memory on ConsensusManager, not in Persistent, so the on-disk format is untouched. `/profiler/consensus_lag` collects those rings from every peer over a new internal RPC and lines them up on the entry indices they share. Each entry is measured from whichever peer applied it first, so a lag is never negative; the peer that is first can differ per entry, so the baseline is per entry rather than a single chosen peer. Entries only one peer still remembers are excluded, otherwise a peer would be measured against itself. A peer stalled part-way through an entry keeps healthy lag statistics - everything it did apply, it applied on time - so the report carries `behind_entries` and `newest_applied_age_ms` alongside, which is what actually exposes the stall. Peers that fail or time out are listed rather than failing the request: a partial answer is more useful than none when the point is to find a peer that stopped answering. The endpoint follows `/profiler/slow_requests`: manage access, and outside OpenAPI, so no endpoint-count or ACTION_ACCESS guard applies. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> * Move applied-entry log into its own module Keeps the new code out of files that are already large. The ring, its entry type and the snapshot served over RPC move to `content_manager/consensus/applied_log.rs`, alongside the other consensus internals; `ConsensusManager` is left with a field, an accessor and the one `record` call in the apply loop. The grpc encoding moves next to the decoding it mirrors, in `common/consensus_lag.rs`, leaving the internal service handler three lines instead of thirty. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> * Test that a consensus stall is still in the report after the peer catches up * Take each peer's applied index from consensus state, not its ring --------- Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com> Co-authored-by: tellet-q <elena.dubrovina@qdrant.com>