Log partition processor effective-leadership readiness and bootstrap duration

become_leader runs synchronous initialization (invoker construction,
active-lock load, a legacy invocation-status scan, actuator setup,
durability read) before the partition transitions to effective
leadership. There was no info-level signal marking that transition or
how long it took to get there -- only a coarse, scrape-interval-limited
gauge and a debug-only "resumed invocations" line. Add one structured
INFO log at the readiness point, with the epoch and elapsed bootstrap
duration, so failover latency can be measured from logs.

Author: pcholakov

crates/worker/src/partition/leadership/mod.rs

@@ -24,7 +24,7 @@ use futures::{StreamExt, TryStreamExt};
 use tokio::sync::mpsc;
 use tokio::time::Instant;
 use tokio_stream::wrappers::ReceiverStream;
-use tracing::{debug, instrument, warn};
+use tracing::{debug, info, instrument, warn};
 
 use restate_core::network::{Oneshot, Reciprocal, TransportConnect};
 use restate_core::{Metadata, ShutdownError, TaskCenter, TaskKind};
@@ -458,6 +458,7 @@ where
         mut processor: impl Processor + HasTrimQueue + HasVQueuesMut,
         partition_store: &mut PartitionStore,
     ) -> Result<(), Error> {
+        let become_leader_started_at = tokio::time::Instant::now();
         let prev_mode = self.detailed_effective_mode();
 
         if let State::Candidate {
@@ -715,9 +716,10 @@ where
                 at.elapsed().friendly(),
             );
 
+            let leader_epoch = *leader_epoch;
             self.state = State::Leader(Box::new(LeaderState::new(
                 processor.partition_id(),
-                *leader_epoch,
+                leader_epoch,
                 processor.key_range(),
                 shuffle_task_handle,
                 cleaner_handle,
@@ -737,6 +739,12 @@ where
                 node_ctx.rule_book_cache.subscribe(),
             )));
 
+            info!(
+                leader_epoch = %leader_epoch,
+                bootstrap_duration = ?become_leader_started_at.elapsed(),
+                "Partition processor reached effective leadership"
+            );
+
             Ok(())
         } else {
             unreachable!("Can only become the leader if I was the candidate before!");