Add JSON export pipeline + event recorder for visualization

The simulation now optionally records structured events (message creation,
delivery, round computation, voting, leader election) via EventRecorder and
exports a complete simulation dump to JSON via the new export_json module.
crisis_data.json captures a 10-step run that the SwiftUI visualizer consumes.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/crisis/demo.py

@@ -28,6 +28,10 @@ from crisis.crypto import digest
 from crisis.graph import LamportGraph
 from crisis.message import Message, Vertex, ID_LENGTH, NONCE_LENGTH
 from crisis.order import LeaderStream, compute_order
+from crisis.recorder import (
+    EventRecorder, EventType, capture_snapshot,
+    record_rounds, record_voting, record_leader_election,
+)
 from crisis.rounds import compute_rounds, max_round, last_vertices_in_round
 from crisis.voting import compute_safe_voting_pattern, compute_virtual_leader_election
 from crisis.weight import ProofOfWorkWeight, DifficultyOracle
@@ -79,11 +83,13 @@ class Simulation:
 
     def __init__(self, num_honest: int = 3, num_byzantine: int = 0,
                  pow_zeros: int = 2, difficulty: int = 1,
-                 connectivity_k: int = 0, seed: int = 42):
+                 connectivity_k: int = 0, seed: int = 42,
+                 recorder: Optional[EventRecorder] = None):
         self.difficulty_oracle = DifficultyOracle(constant_difficulty=difficulty)
         self.connectivity_k = connectivity_k
         self.weight_system = ProofOfWorkWeight(min_leading_zeros=pow_zeros)
         self.seed = seed
+        self.recorder = recorder
         random.seed(seed)
 
         # Create nodes
@@ -106,6 +112,7 @@ class Simulation:
 
         self.step_count = 0
         self.all_messages: list[Message] = []
+        self.snapshots: list[capture_snapshot.__class__] = []  # type: ignore
 
     def step(self) -> dict:
         """Execute one simulation step.
@@ -113,6 +120,12 @@ class Simulation:
         Returns a dict with step results for display.
         """
         self.step_count += 1
+        rec = self.recorder
+
+        if rec:
+            rec.record(self.step_count, EventType.STEP_BEGIN, "",
+                       sim_step=self.step_count)
+
         step_results = {
             "step": self.step_count,
             "new_messages": [],
@@ -130,57 +143,99 @@ class Simulation:
 
             if msg is not None:
                 new_messages.append((node, msg))
+                msg_digest = msg.compute_digest().hex()[:12]
+                msg_weight = self.weight_system.weight(msg)
+
                 step_results["new_messages"].append({
                     "from": node.name,
-                    "digest": msg.compute_digest().hex()[:12],
-                    "weight": self.weight_system.weight(msg),
+                    "digest": msg_digest,
+                    "weight": msg_weight,
                     "payload": msg.payload.decode(errors="replace"),
                 })
 
+                if rec:
+                    evt = EventType.BYZANTINE_MUTATION if node.is_byzantine else EventType.MESSAGE_CREATED
+                    rec.record(
+                        self.step_count, evt, node.name,
+                        digest_hex=msg_digest,
+                        process_id_hex=msg.id.hex()[:8],
+                        payload_str=msg.payload.decode(errors="replace")[:60],
+                        weight=msg_weight,
+                        num_refs=len(msg.digests),
+                    )
+
         # Phase 2: Gossip -- deliver all messages to all nodes
         for source_node, msg in new_messages:
             self.all_messages.append(msg)
             for target_node in self.nodes:
-                # Deliver to all nodes (including source, for consistency)
-                target_node.graph.extend(msg)
+                result = target_node.graph.extend(msg)
+                if rec and result is not None:
+                    rec.record(
+                        self.step_count, EventType.MESSAGE_DELIVERED, target_node.name,
+                        digest_hex=msg.compute_digest().hex()[:12],
+                        from_node=source_node.name,
+                    )
 
         # Also re-deliver older messages that nodes might be missing
-        # (simulates pull gossip catching up)
         for msg in self.all_messages:
             for node in self.nodes:
-                node.graph.extend(msg)  # extend() is idempotent (integrity check)
+                node.graph.extend(msg)  # extend() is idempotent
 
         # Phase 3: Compute consensus on each node
+        self._last_orders: dict[str, list] = {}
         for node in self.nodes:
-            compute_rounds(node.graph, self.difficulty_oracle, self.connectivity_k)
+            if rec:
+                record_rounds(node.graph, self.difficulty_oracle,
+                              self.connectivity_k, rec,
+                              self.step_count, node.name)
+            else:
+                compute_rounds(node.graph, self.difficulty_oracle,
+                               self.connectivity_k)
 
             # Compute SVP for all last vertices
             for vertex in node.graph.all_vertices():
                 if vertex.is_last:
-                    compute_safe_voting_pattern(
-                        vertex, node.graph, self.difficulty_oracle,
-                        self.connectivity_k
-                    )
+                    if rec:
+                        record_voting(vertex, node.graph,
+                                      self.difficulty_oracle,
+                                      self.connectivity_k, rec,
+                                      self.step_count, node.name)
+                    else:
+                        compute_safe_voting_pattern(
+                            vertex, node.graph, self.difficulty_oracle,
+                            self.connectivity_k
+                        )
 
-            # Compute leader election in round order (lower rounds first).
-            # This ensures that when a higher-round vertex reads votes from
-            # its voting set members, those members have already computed
-            # their own votes.
+            # Compute leader election in round order
             leader_dict: dict[int, list[tuple[int, Message]]] = {}
             svp_vertices = [v for v in node.graph.all_vertices() if v.svp]
             svp_vertices.sort(key=lambda v: v.round if v.round is not None else 0)
 
             for vertex in svp_vertices:
-                compute_virtual_leader_election(
-                    vertex, node.graph, self.difficulty_oracle,
-                    self.connectivity_k, leader_dict
-                )
+                if rec:
+                    record_leader_election(
+                        vertex, node.graph, self.difficulty_oracle,
+                        self.connectivity_k, leader_dict, rec,
+                        self.step_count, node.name
+                    )
+                else:
+                    compute_virtual_leader_election(
+                        vertex, node.graph, self.difficulty_oracle,
+                        self.connectivity_k, leader_dict
+                    )
 
             for round_num, entries in leader_dict.items():
                 for deciding_round, leader_msg in entries:
                     node.leader_stream.update(round_num, deciding_round, leader_msg)
 
             ordered = compute_order(node.graph, node.leader_stream)
+            self._last_orders[node.name] = ordered
+
+            if rec:
+                rec.record(
+                    self.step_count, EventType.ORDER_COMPUTED, node.name,
+                    count=len(ordered),
+                )
 
             mr = max_round(node.graph)
             step_results["node_states"].append({
@@ -192,6 +247,10 @@ class Simulation:
                 "is_byzantine": node.is_byzantine,
             })
 
+        if rec:
+            rec.record(self.step_count, EventType.STEP_END, "",
+                       sim_step=self.step_count)
+
         return step_results
 
     def _byzantine_message(self, node: SimulatedNode) -> Optional[Message]:
@@ -221,15 +280,39 @@ class Simulation:
         else:
             return node.generate_message(payload)
 
-    def run(self, num_steps: int = 10, verbose: bool = True) -> list[dict]:
-        """Run the simulation for a number of steps."""
+    def run(self, num_steps: int = 10, verbose: bool = True,
+            progress_callback=None) -> list[dict]:
+        """Run the simulation for a number of steps.
+
+        Args:
+            num_steps: Number of simulation steps to run.
+            verbose: Print step results to stdout.
+            progress_callback: Optional callable(step, total) for progress UI.
+        """
         results = []
-        for _ in range(num_steps):
+        for i in range(num_steps):
             result = self.step()
             results.append(result)
             if verbose:
                 _print_step(result)
 
+            # Capture snapshot for visualization
+            if self.recorder:
+                snap = capture_snapshot(self.step_count, self.nodes,
+                                        self.weight_system,
+                                        precomputed_orders=self._last_orders)
+                self.recorder.snapshots.append(snap)
+
+                # Convergence check event
+                self.recorder.record(
+                    self.step_count, EventType.CONVERGENCE_CHECK, "",
+                    convergence=snap.convergence,
+                    agreed_prefix=snap.agreed_prefix_length,
+                )
+
+            if progress_callback:
+                progress_callback(i + 1, num_steps)
+
         if verbose:
             _print_convergence_summary(self)
 

src/crisis/export_json.py

@@ -0,0 +1,176 @@
+"""
+JSON Exporter — Exports simulation data for the native macOS visualizer.
+
+Runs the simulation and writes a complete JSON file containing:
+  - Configuration parameters
+  - Per-step snapshots (vertices, edges, rounds, leaders, order)
+  - Per-step events (message creation, gossip, round assignment, etc.)
+
+Usage:
+    python -m crisis.export_json [--nodes 8] [--steps 10] [-o crisis_data.json]
+"""
+
+from __future__ import annotations
+
+import json
+import sys
+import argparse
+from dataclasses import asdict
+
+from crisis.demo import Simulation
+from crisis.recorder import EventRecorder, EventType
+
+
+def export_simulation(
+    num_honest: int = 8,
+    num_byzantine: int = 1,
+    num_steps: int = 10,
+    pow_zeros: int = 1,
+    difficulty: int = 1,
+    connectivity_k: int = 0,
+    seed: int = 42,
+) -> dict:
+    """Run simulation and return exportable dict."""
+    recorder = EventRecorder()
+    sim = Simulation(
+        num_honest=num_honest,
+        num_byzantine=num_byzantine,
+        pow_zeros=pow_zeros,
+        difficulty=difficulty,
+        connectivity_k=connectivity_k,
+        seed=seed,
+        recorder=recorder,
+    )
+    sim.run(num_steps=num_steps, verbose=False)
+
+    # Node metadata
+    from crisis.crypto import digest
+    from crisis.message import ID_LENGTH
+    node_meta = []
+    for n in sim.nodes:
+        pid = digest(n.name.encode())[:ID_LENGTH].hex()[:8]
+        node_meta.append({
+            "name": n.name,
+            "processIdHex": pid,
+            "isByzantine": n.is_byzantine,
+        })
+
+    # Config
+    config = {
+        "numHonest": num_honest,
+        "numByzantine": num_byzantine,
+        "numSteps": num_steps,
+        "powZeros": pow_zeros,
+        "difficulty": difficulty,
+        "connectivityK": connectivity_k,
+        "seed": seed,
+    }
+
+    # Snapshots
+    steps_data = []
+    for snap in recorder.snapshots:
+        step_obj = {
+            "step": snap.step,
+            "convergence": snap.convergence,
+            "agreedPrefixLength": snap.agreed_prefix_length,
+            "nodeSnapshots": {},
+        }
+        for name, ns in snap.node_snapshots.items():
+            vertices = []
+            for v in ns.vertices:
+                vertices.append({
+                    "digestHex": v.digest_hex,
+                    "digestFull": v.digest_full,
+                    "processIdHex": v.process_id_hex,
+                    "roundNumber": v.round_number,
+                    "isLast": v.is_last,
+                    "weight": v.weight,
+                    "payloadStr": v.payload_str,
+                    "totalPosition": v.total_position,
+                    "isByzantineSource": v.is_byzantine_source,
+                })
+            edges = [{"from": e[0], "to": e[1]} for e in ns.edges]
+            leader_rounds = {str(k): v for k, v in ns.leader_rounds.items()}
+            step_obj["nodeSnapshots"][name] = {
+                "name": ns.name,
+                "vertexCount": ns.vertex_count,
+                "maxRound": ns.max_round,
+                "numLeaders": ns.num_leaders,
+                "numOrdered": ns.num_ordered,
+                "isByzantine": ns.is_byzantine,
+                "vertices": vertices,
+                "edges": edges,
+                "leaderRounds": leader_rounds,
+            }
+        steps_data.append(step_obj)
+
+    # Events (grouped by step)
+    events_by_step: dict[int, list] = {}
+    for e in recorder.events:
+        step = e.step
+        if step not in events_by_step:
+            events_by_step[step] = []
+        events_by_step[step].append({
+            "seq": e.seq,
+            "type": e.event_type.name,
+            "nodeName": e.node_name,
+            "data": _clean_data(e.data),
+        })
+
+    return {
+        "config": config,
+        "nodes": node_meta,
+        "steps": steps_data,
+        "events": events_by_step,
+    }
+
+
+def _clean_data(data: dict) -> dict:
+    """Ensure all values are JSON-serializable."""
+    clean = {}
+    for k, v in data.items():
+        if isinstance(v, bytes):
+            clean[k] = v.hex()
+        elif isinstance(v, (int, float, str, bool, type(None))):
+            clean[k] = v
+        elif isinstance(v, (list, tuple)):
+            clean[k] = [x.hex() if isinstance(x, bytes) else x for x in v]
+        elif isinstance(v, dict):
+            clean[k] = _clean_data(v)
+        else:
+            clean[k] = str(v)
+    return clean
+
+
+def main():
+    parser = argparse.ArgumentParser(description="Export Crisis simulation to JSON")
+    parser.add_argument("--nodes", type=int, default=8)
+    parser.add_argument("--byzantine", type=int, default=1)
+    parser.add_argument("--steps", type=int, default=10)
+    parser.add_argument("--pow-zeros", type=int, default=1)
+    parser.add_argument("--difficulty", type=int, default=1)
+    parser.add_argument("--connectivity-k", type=int, default=0)
+    parser.add_argument("--seed", type=int, default=42)
+    parser.add_argument("-o", "--output", default="crisis_data.json")
+    args = parser.parse_args()
+
+    data = export_simulation(
+        num_honest=args.nodes,
+        num_byzantine=args.byzantine,
+        num_steps=args.steps,
+        pow_zeros=args.pow_zeros,
+        difficulty=args.difficulty,
+        connectivity_k=args.connectivity_k,
+        seed=args.seed,
+    )
+
+    with open(args.output, "w") as f:
+        json.dump(data, f, indent=2)
+
+    n_events = sum(len(v) for v in data["events"].values())
+    n_snaps = len(data["steps"])
+    print(f"Exported: {n_events} events, {n_snaps} snapshots → {args.output}")
+
+
+if __name__ == "__main__":
+    main()

src/crisis/graph.py

@@ -60,6 +60,10 @@ class LamportGraph:
         # digest -> set of digests that reference this vertex
         self.reverse_edges: dict[bytes, set[bytes]] = {}
 
+        # Cache for past() results: digest -> frozenset of digests
+        # Invalidated when new vertices are added via extend()
+        self._past_cache: dict[bytes, frozenset[bytes]] = {}
+
     # ------------------------------------------------------------------
     # Graph queries
     # ------------------------------------------------------------------
@@ -124,8 +128,13 @@ class LamportGraph:
         Returns the set of all vertices that are causally before v
         (including v itself -- reflexivity).
         """
+        d = v.message_digest
+        cached = self._past_cache.get(d)
+        if cached is not None:
+            return {self.vertices[dd] for dd in cached if dd in self.vertices}
+
         visited: set[bytes] = set()
-        stack = [v.message_digest]
+        stack = [d]
 
         while stack:
             current = stack.pop()
@@ -136,7 +145,8 @@ class LamportGraph:
                 if neighbor in self.vertices and neighbor not in visited:
                     stack.append(neighbor)
 
-        return {self.vertices[d] for d in visited if d in self.vertices}
+        self._past_cache[d] = frozenset(visited)
+        return {self.vertices[dd] for dd in visited if dd in self.vertices}
 
     def future(self, v: Vertex) -> set[Vertex]:
         """All vertices that are causally after v (including v itself)."""

src/crisis/recorder.py

@@ -0,0 +1,309 @@
+"""
+Event Recording System for Crisis Protocol Visualization
+
+Records all protocol events during a simulation run, producing a structured
+event log and per-step snapshots.  The visualization application replays
+these recordings with full timeline control.
+
+Design: instrumentation wrappers diff state before/after calling the original
+protocol functions, so the core algorithm files remain unmodified.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from enum import Enum, auto
+from typing import Any, Optional
+
+from crisis.graph import LamportGraph
+from crisis.message import Vertex
+from crisis.order import LeaderStream, compute_order
+from crisis.rounds import compute_rounds, max_round
+from crisis.voting import (
+    compute_safe_voting_pattern,
+    compute_virtual_leader_election,
+)
+from crisis.weight import DifficultyOracle
+
+
+# ---------------------------------------------------------------------------
+# Event Types
+# ---------------------------------------------------------------------------
+
+class EventType(Enum):
+    # Phase 1: Message generation
+    MESSAGE_CREATED = auto()
+    BYZANTINE_MUTATION = auto()
+
+    # Phase 2: Gossip / delivery
+    MESSAGE_DELIVERED = auto()
+
+    # Phase 3: Consensus
+    ROUND_ASSIGNED = auto()
+    VERTEX_BECOMES_LAST = auto()
+    SVP_COMPUTED = auto()
+    VOTE_CAST = auto()
+    LEADER_ELECTED = auto()
+    ORDER_COMPUTED = auto()
+
+    # Meta
+    STEP_BEGIN = auto()
+    STEP_END = auto()
+    CONVERGENCE_CHECK = auto()
+
+
+# ---------------------------------------------------------------------------
+# Event
+# ---------------------------------------------------------------------------
+
+@dataclass(frozen=True)
+class SimEvent:
+    """A single recorded protocol event."""
+    seq: int
+    step: int
+    event_type: EventType
+    node_name: str
+    data: dict[str, Any]
+
+
+# ---------------------------------------------------------------------------
+# Snapshots
+# ---------------------------------------------------------------------------
+
+@dataclass
+class VertexSnapshot:
+    """Snapshot of a single vertex at a point in time."""
+    digest_hex: str          # 12-char hex prefix for display
+    digest_full: str         # full hex for lookup
+    process_id_hex: str      # 8-char hex prefix
+    round_number: Optional[int] = None
+    is_last: bool = False
+    weight: int = 0
+    payload_str: str = ""
+    total_position: Optional[int] = None
+    svp: list[int] = field(default_factory=list)
+    is_byzantine_source: bool = False
+
+
+@dataclass
+class NodeSnapshot:
+    """Snapshot of a node's full state at a given step."""
+    name: str
+    step: int
+    vertex_count: int = 0
+    max_round: int = 0
+    num_leaders: int = 0
+    num_ordered: int = 0
+    is_byzantine: bool = False
+    vertices: list[VertexSnapshot] = field(default_factory=list)
+    edges: list[tuple[str, str]] = field(default_factory=list)  # (from_hex, to_hex)
+    leader_rounds: dict[int, str] = field(default_factory=dict)  # round -> leader digest_hex
+
+
+@dataclass
+class StepSnapshot:
+    """Full simulation state captured at a step boundary."""
+    step: int
+    node_snapshots: dict[str, NodeSnapshot] = field(default_factory=dict)
+    convergence: bool = False
+    agreed_prefix_length: int = 0
+
+
+# ---------------------------------------------------------------------------
+# EventRecorder
+# ---------------------------------------------------------------------------
+
+class EventRecorder:
+    """Accumulates events and snapshots during a simulation run."""
+
+    def __init__(self):
+        self.events: list[SimEvent] = []
+        self.snapshots: list[StepSnapshot] = []
+        self._seq = 0
+
+    def record(self, step: int, event_type: EventType,
+               node_name: str, **data) -> SimEvent:
+        self._seq += 1
+        event = SimEvent(self._seq, step, event_type, node_name, data)
+        self.events.append(event)
+        return event
+
+    def events_at_step(self, step: int) -> list[SimEvent]:
+        return [e for e in self.events if e.step == step]
+
+    def events_of_type(self, et: EventType) -> list[SimEvent]:
+        return [e for e in self.events if e.event_type == et]
+
+    def max_step(self) -> int:
+        return max((e.step for e in self.events), default=0)
+
+
+# ---------------------------------------------------------------------------
+# Snapshot capture
+# ---------------------------------------------------------------------------
+
+def capture_snapshot(step: int, nodes, weight_system,
+                     precomputed_orders: dict | None = None) -> StepSnapshot:
+    """Capture a full StepSnapshot from the current simulation state.
+
+    Args:
+        step: The simulation step number.
+        nodes: List of SimulatedNode objects.
+        weight_system: The weight system for computing vertex weights.
+        precomputed_orders: Optional dict node_name -> list[Vertex] to skip
+            recomputing total order (expensive).
+    """
+    snap = StepSnapshot(step=step)
+
+    for node in nodes:
+        g = node.graph
+        mr = max_round(g)
+        if precomputed_orders and node.name in precomputed_orders:
+            ordered = precomputed_orders[node.name]
+        else:
+            ordered = compute_order(g, node.leader_stream)
+
+        # Build vertex snapshots
+        v_snaps = []
+        for v in g.all_vertices():
+            vs = VertexSnapshot(
+                digest_hex=v.message_digest.hex()[:12],
+                digest_full=v.message_digest.hex(),
+                process_id_hex=v.id.hex()[:8],
+                round_number=v.round,
+                is_last=bool(v.is_last),
+                weight=weight_system.weight(v.m),
+                payload_str=v.payload.decode(errors="replace")[:60],
+                total_position=v.total_position,
+                svp=list(v.svp) if v.svp else [],
+            )
+            v_snaps.append(vs)
+
+        # Build edge list
+        edge_list = []
+        for d_from, refs in g.edges.items():
+            from_hex = d_from.hex()[:12]
+            for d_to in refs:
+                if d_to in g.vertices:
+                    edge_list.append((from_hex, d_to.hex()[:12]))
+
+        # Leader digest map
+        leader_rounds = {}
+        for rn, (_, msg) in node.leader_stream.leaders.items():
+            leader_rounds[rn] = msg.compute_digest().hex()[:12]
+
+        ns = NodeSnapshot(
+            name=node.name,
+            step=step,
+            vertex_count=g.vertex_count(),
+            max_round=mr,
+            num_leaders=len(node.leader_stream.leaders),
+            num_ordered=len(ordered),
+            is_byzantine=node.is_byzantine,
+            vertices=v_snaps,
+            edges=edge_list,
+            leader_rounds=leader_rounds,
+        )
+        snap.node_snapshots[node.name] = ns
+
+    # Convergence check across honest nodes
+    honest = [n for n in nodes if not n.is_byzantine]
+    if len(honest) >= 2:
+        orders = []
+        for n in honest:
+            if precomputed_orders and n.name in precomputed_orders:
+                o = precomputed_orders[n.name]
+            else:
+                o = compute_order(n.graph, n.leader_stream)
+            orders.append([v.message_digest.hex()[:12] for v in o])
+        # Find longest common prefix
+        if orders:
+            min_len = min(len(o) for o in orders)
+            agreed = 0
+            for i in range(min_len):
+                if all(o[i] == orders[0][i] for o in orders[1:]):
+                    agreed = i + 1
+                else:
+                    break
+            snap.agreed_prefix_length = agreed
+            snap.convergence = (agreed == min_len and min_len > 0
+                                and all(len(o) == len(orders[0]) for o in orders))
+
+    return snap
+
+
+# ---------------------------------------------------------------------------
+# Instrumentation wrappers
+# ---------------------------------------------------------------------------
+
+def record_rounds(graph: LamportGraph, difficulty: DifficultyOracle,
+                  connectivity_k: int, recorder: EventRecorder,
+                  step: int, node_name: str) -> None:
+    """Wrapper around compute_rounds that records state changes."""
+    old_state = {
+        v.message_digest: (v.round, v.is_last)
+        for v in graph.all_vertices()
+    }
+
+    compute_rounds(graph, difficulty, connectivity_k)
+
+    for v in graph.all_vertices():
+        d = v.message_digest
+        old_r, old_last = old_state.get(d, (None, None))
+        if v.round != old_r and v.round is not None:
+            recorder.record(
+                step, EventType.ROUND_ASSIGNED, node_name,
+                digest_hex=d.hex()[:12],
+                round_number=v.round,
+                process_id_hex=v.id.hex()[:8],
+            )
+        if v.is_last and not old_last:
+            recorder.record(
+                step, EventType.VERTEX_BECOMES_LAST, node_name,
+                digest_hex=d.hex()[:12],
+                round_number=v.round,
+                process_id_hex=v.id.hex()[:8],
+            )
+
+
+def record_voting(vertex: Vertex, graph: LamportGraph,
+                  difficulty: DifficultyOracle, connectivity_k: int,
+                  recorder: EventRecorder, step: int,
+                  node_name: str) -> None:
+    """Wrapper around compute_safe_voting_pattern that records SVP."""
+    old_svp = list(vertex.svp) if vertex.svp else []
+
+    compute_safe_voting_pattern(vertex, graph, difficulty, connectivity_k)
+
+    if vertex.svp and vertex.svp != old_svp:
+        recorder.record(
+            step, EventType.SVP_COMPUTED, node_name,
+            digest_hex=vertex.message_digest.hex()[:12],
+            svp=list(vertex.svp),
+            round_number=vertex.round,
+        )
+
+
+def record_leader_election(vertex: Vertex, graph: LamportGraph,
+                           difficulty: DifficultyOracle,
+                           connectivity_k: int,
+                           leader_dict: dict,
+                           recorder: EventRecorder, step: int,
+                           node_name: str) -> None:
+    """Wrapper around compute_virtual_leader_election that records results."""
+    old_keys = set(leader_dict.keys())
+
+    compute_virtual_leader_election(
+        vertex, graph, difficulty, connectivity_k, leader_dict
+    )
+
+    new_keys = set(leader_dict.keys()) - old_keys
+    for rn in new_keys:
+        entries = leader_dict[rn]  # list[tuple[int, Message]]
+        for deciding_round, leader_msg in entries:
+            recorder.record(
+                step, EventType.LEADER_ELECTED, node_name,
+                round_number=rn,
+                deciding_round=deciding_round,
+                leader_digest_hex=leader_msg.compute_digest().hex()[:12],
+            )