Add iteration trace diagnostics for seed43

DOCS.md

@@ -130,6 +130,7 @@ Use `RoutingProblem.initial_paths` to provide semantic per-net seeds. Seeds are
 | `capture_expanded` | `False` | Record expanded nodes for diagnostics and visualization. |
 | `capture_conflict_trace` | `False` | Capture authoritative post-reverify conflict trace entries for debugging negotiated-congestion failures. |
 | `capture_frontier_trace` | `False` | Run an analysis-only reroute for reached-but-colliding nets and capture prune causes near their final conflict hotspots. |
+| `capture_iteration_trace` | `False` | Capture per-iteration and per-net route-attempt attribution for negotiated-congestion diagnosis. |
 
 ## 7. Conflict Trace
 
@@ -186,7 +187,37 @@ Use `scripts/record_frontier_trace.py` to capture JSON and Markdown frontier-pru
 
 Separately from the observational trace tooling, the router may run a bounded post-loop pair-local scratch reroute before refinement when the restored best snapshot ends with final two-net reached-target dynamic conflicts. That repair phase is part of normal routing behavior and is reported through the `pair_local_search_*` counters below.
 
-## 9. RouteMetrics
+## 9. Iteration Trace
+
+`RoutingRunResult.iteration_trace` is an immutable tuple of negotiated-congestion iteration summaries. It is empty unless `RoutingOptions.diagnostics.capture_iteration_trace=True`.
+
+Trace types:
+
+- `IterationTraceEntry`
+  - `iteration`
+  - `congestion_penalty`: Penalty in effect for that iteration
+  - `routed_net_ids`: Nets rerouted during that iteration, in routing order
+  - `completed_nets`
+  - `conflict_edges`
+  - `total_dynamic_collisions`
+  - `nodes_expanded`
+  - `congestion_check_calls`
+  - `congestion_candidate_ids`
+  - `congestion_exact_pair_checks`
+  - `net_attempts`: Per-net attribution for that iteration
+- `IterationNetAttemptTrace`
+  - `net_id`
+  - `reached_target`
+  - `nodes_expanded`
+  - `congestion_check_calls`
+  - `pruned_closed_set`
+  - `pruned_cost`
+  - `pruned_hard_collision`
+  - `guidance_seed_present`
+
+Use `scripts/record_iteration_trace.py` to capture JSON and Markdown iteration-attribution artifacts. Its default comparison target is the solved seed-42 no-warm canary versus the pathological seed-43 no-warm canary.
+
+## 10. RouteMetrics
 
 `RoutingRunResult.metrics` is an immutable per-run snapshot.
 
@@ -272,7 +303,7 @@ Separately from the observational trace tooling, the router may run a bounded po
 Lower-level search and collision modules are semi-private implementation details. They remain accessible through deep imports for advanced use, but they are unstable and may change without notice. The stable supported entrypoint is `route(problem, options=...)`.
 
 The current implementation structure is summarized in **[docs/architecture.md](docs/architecture.md)**. The committed example-corpus counter baseline is tracked in **[docs/performance.md](docs/performance.md)**.
-Use `scripts/diff_performance_baseline.py` to compare a fresh local run against that baseline. Use `scripts/record_conflict_trace.py` for opt-in conflict-hotspot traces, `scripts/record_frontier_trace.py` for hotspot-adjacent prune traces, and `scripts/characterize_pair_local_search.py` to sweep example_07-style no-warm runs for pair-local repair behavior. The counter baseline is currently observational and is not enforced as a CI gate.
+Use `scripts/diff_performance_baseline.py` to compare a fresh local run against that baseline. Use `scripts/record_conflict_trace.py` for opt-in conflict-hotspot traces, `scripts/record_frontier_trace.py` for hotspot-adjacent prune traces, `scripts/record_iteration_trace.py` for per-iteration negotiated-congestion attribution, and `scripts/characterize_pair_local_search.py` to sweep example_07-style no-warm runs for pair-local repair behavior. The counter baseline is currently observational and is not enforced as a CI gate.
 
 ## 11. Tuning Notes
 

docs/iteration_trace.md

@@ -0,0 +1,85 @@
+# Iteration Trace
+
+Generated at 2026-04-02T16:11:39-07:00 by `scripts/record_iteration_trace.py`.
+
+## example_07_large_scale_routing_no_warm_start
+
+Results: 10 valid / 10 reached / 10 total.
+
+| Iteration | Penalty | Routed Nets | Completed | Conflict Edges | Dynamic Collisions | Nodes | Congestion Checks | Candidate Ids | Exact Pairs |
+| --: | --: | --: | --: | --: | --: | --: | --: | --: | --: |
+| 0 | 100.0 | 10 | 1 | 16 | 50 | 571 | 0 | 0 | 0 |
+| 1 | 140.0 | 10 | 2 | 12 | 54 | 253 | 974 | 2378 | 1998 |
+| 2 | 196.0 | 10 | 4 | 5 | 22 | 253 | 993 | 1928 | 1571 |
+| 3 | 274.4 | 10 | 6 | 2 | 10 | 100 | 437 | 852 | 698 |
+| 4 | 384.2 | 10 | 6 | 2 | 10 | 126 | 517 | 961 | 812 |
+| 5 | 537.8 | 10 | 6 | 2 | 10 | 461 | 1704 | 3805 | 3043 |
+
+Top nets by iteration-attributed nodes expanded:
+
+- `net_03`: 383
+- `net_06`: 292
+- `net_09`: 260
+- `net_00`: 210
+- `net_02`: 190
+- `net_08`: 168
+- `net_01`: 162
+- `net_07`: 61
+- `net_04`: 19
+- `net_05`: 19
+
+Top nets by iteration-attributed congestion checks:
+
+- `net_03`: 1242
+- `net_06`: 1080
+- `net_02`: 674
+- `net_01`: 534
+- `net_08`: 262
+- `net_00`: 229
+- `net_07`: 228
+- `net_09`: 176
+- `net_04`: 100
+- `net_05`: 100
+
+## example_07_large_scale_routing_no_warm_start_seed43
+
+Results: 10 valid / 10 reached / 10 total.
+
+| Iteration | Penalty | Routed Nets | Completed | Conflict Edges | Dynamic Collisions | Nodes | Congestion Checks | Candidate Ids | Exact Pairs |
+| --: | --: | --: | --: | --: | --: | --: | --: | --: | --: |
+| 0 | 100.0 | 10 | 1 | 16 | 50 | 571 | 0 | 0 | 0 |
+| 1 | 140.0 | 10 | 1 | 13 | 53 | 269 | 961 | 2562 | 2032 |
+| 2 | 196.0 | 10 | 4 | 3 | 15 | 140 | 643 | 1610 | 1224 |
+| 3 | 274.4 | 10 | 4 | 3 | 15 | 84 | 382 | 801 | 651 |
+| 4 | 384.2 | 10 | 6 | 2 | 10 | 170 | 673 | 1334 | 1072 |
+| 5 | 537.8 | 10 | 6 | 2 | 10 | 457 | 1671 | 3718 | 2992 |
+| 6 | 753.0 | 10 | 4 | 4 | 8 | 22288 | 89671 | 218513 | 171925 |
+| 7 | 1054.1 | 10 | 4 | 4 | 8 | 15737 | 29419 | 34309 | 28603 |
+| 8 | 1475.8 | 10 | 4 | 4 | 8 | 21543 | 41803 | 49314 | 41198 |
+
+Top nets by iteration-attributed nodes expanded:
+
+- `net_06`: 31604
+- `net_03`: 27532
+- `net_02`: 763
+- `net_09`: 286
+- `net_07`: 239
+- `net_00`: 233
+- `net_08`: 218
+- `net_05`: 134
+- `net_01`: 132
+- `net_04`: 118
+
+Top nets by iteration-attributed congestion checks:
+
+- `net_06`: 83752
+- `net_03`: 75019
+- `net_02`: 3270
+- `net_07`: 844
+- `net_08`: 540
+- `net_01`: 441
+- `net_05`: 425
+- `net_04`: 398
+- `net_09`: 288
+- `net_00`: 246
+

docs/optimization_pass_01_log.md

@@ -3629,3 +3629,14 @@ Findings:
 | example_07_large_scale_routing_no_warm_start | pair_local_search_attempts | - | 2.0000 | - |
 | example_07_large_scale_routing_no_warm_start | pair_local_search_accepts | - | 2.0000 | - |
 | example_07_large_scale_routing_no_warm_start | pair_local_search_nodes_expanded | - | 68.0000 | - |
+
+## Step 64 seed-43 iteration-trace diagnosis
+
+Measured on 2026-04-02T16:11:39-07:00.
+
+Findings:
+
+- Added `capture_iteration_trace` plus `scripts/record_iteration_trace.py` and tracked the first `seed 42` vs `seed 43` no-warm comparison in `docs/iteration_trace.json` and `docs/iteration_trace.md`.
+- The pathological `seed 43` basin is not front-loaded. It matches the solved `seed 42` path through iteration `5`, then falls into three extra iterations with only `4` completed nets and `4` conflict edges.
+- The late blowup is concentrated in two nets, not the whole routing set: `net_06` contributes `31604` attributed nodes and `83752` congestion checks, while `net_03` contributes `27532` nodes and `75019` congestion checks.
+- This points the next optimization work at late-iteration reroute behavior for a small subset of nets rather than another global congestion or pair-local-search change.

docs/performance.md

@@ -9,6 +9,7 @@ The default baseline table below covers the standard example corpus only. The he
 
 Use `scripts/characterize_pair_local_search.py` when you want a small parameter sweep over example_07-style no-warm runs instead of a single canary reading.
 The current tracked sweep output lives in `docs/pair_local_characterization.json` and `docs/pair_local_characterization.md`.
+Use `scripts/record_iteration_trace.py` when you want a seed-42 vs seed-43 negotiated-congestion attribution run; the current tracked output lives in `docs/iteration_trace.json` and `docs/iteration_trace.md`.
 
 | Scenario | Duration (s) | Total | Valid | Reached | Iter | Nets Routed | Nodes | Ray Casts | Moves Gen | Moves Added | Dyn Tree | Visibility Builds | Congestion Checks | Verify Calls |
 | :-- | --: | --: | --: | --: | --: | --: | --: | --: | --: | --: | --: | --: | --: | --: |
@@ -36,6 +37,8 @@ For the current accepted branch, the most important performance-only canary is `
 
 The latest tracked characterization sweep confirms there is no smaller stable pair-local smoke case under the `<=1.0s` rule, so the 10-net no-warm-start canary remains the primary regression target for this behavior.
 
+The tracked iteration trace adds one more diagnosis target: `example_07_large_scale_routing_no_warm_start_seed43`. That seed now remains performance-only, and its blowup is concentrated in late iterations rather than the initial basin. In the current trace, seed `43` matches seed `42` through iteration `5`, then spends three extra iterations with `4` completed nets while `net_03` and `net_06` dominate both `nodes_expanded` and `congestion_check_calls`.
+
 Tracked metric keys:
 
 nodes_expanded, moves_generated, moves_added, pruned_closed_set, pruned_hard_collision, pruned_cost, route_iterations, nets_routed, nets_reached_target, warm_start_paths_built, warm_start_paths_used, refine_path_calls, timeout_events, iteration_reverify_calls, iteration_reverified_nets, iteration_conflicting_nets, iteration_conflict_edges, nets_carried_forward, score_component_calls, score_component_total_ns, path_cost_calls, danger_map_lookup_calls, danger_map_cache_hits, danger_map_cache_misses, danger_map_query_calls, danger_map_total_ns, move_cache_abs_hits, move_cache_abs_misses, move_cache_rel_hits, move_cache_rel_misses, guidance_match_moves, guidance_match_moves_straight, guidance_match_moves_bend90, guidance_match_moves_sbend, guidance_bonus_applied, guidance_bonus_applied_straight, guidance_bonus_applied_bend90, guidance_bonus_applied_sbend, static_safe_cache_hits, hard_collision_cache_hits, congestion_cache_hits, congestion_cache_misses, congestion_presence_cache_hits, congestion_presence_cache_misses, congestion_presence_skips, congestion_candidate_precheck_hits, congestion_candidate_precheck_misses, congestion_candidate_precheck_skips, congestion_grid_net_cache_hits, congestion_grid_net_cache_misses, congestion_grid_span_cache_hits, congestion_grid_span_cache_misses, congestion_candidate_nets, congestion_net_envelope_cache_hits, congestion_net_envelope_cache_misses, dynamic_path_objects_added, dynamic_path_objects_removed, dynamic_tree_rebuilds, dynamic_grid_rebuilds, static_tree_rebuilds, static_raw_tree_rebuilds, static_net_tree_rebuilds, visibility_corner_index_builds, visibility_builds, visibility_corner_pairs_checked, visibility_corner_queries_exact, visibility_corner_hits_exact, visibility_point_queries, visibility_point_cache_hits, visibility_point_cache_misses, visibility_tangent_candidate_scans, visibility_tangent_candidate_corner_checks, visibility_tangent_candidate_ray_tests, ray_cast_calls, ray_cast_calls_straight_static, ray_cast_calls_expand_snap, ray_cast_calls_expand_forward, ray_cast_calls_visibility_build, ray_cast_calls_visibility_query, ray_cast_calls_visibility_tangent, ray_cast_calls_other, ray_cast_candidate_bounds, ray_cast_exact_geometry_checks, congestion_check_calls, congestion_lazy_resolutions, congestion_lazy_requeues, congestion_candidate_ids, congestion_exact_pair_checks, verify_path_report_calls, verify_static_buffer_ops, verify_dynamic_candidate_nets, verify_dynamic_exact_pair_checks, refinement_windows_considered, refinement_static_bounds_checked, refinement_dynamic_bounds_checked, refinement_candidate_side_extents, refinement_candidates_built, refinement_candidates_verified, refinement_candidates_accepted, pair_local_search_pairs_considered, pair_local_search_attempts, pair_local_search_accepts, pair_local_search_nodes_expanded

inire/__init__.py

@@ -18,6 +18,8 @@ from .results import (  # noqa: PLC0414
     ComponentConflictTrace as ComponentConflictTrace,
     ConflictTraceEntry as ConflictTraceEntry,
     FrontierPruneSample as FrontierPruneSample,
+    IterationNetAttemptTrace as IterationNetAttemptTrace,
+    IterationTraceEntry as IterationTraceEntry,
     NetConflictTrace as NetConflictTrace,
     NetFrontierTrace as NetFrontierTrace,
     RoutingResult as RoutingResult,
@@ -47,6 +49,7 @@ def route(
         expanded_nodes=tuple(finder.accumulated_expanded_nodes),
         conflict_trace=tuple(finder.conflict_trace),
         frontier_trace=tuple(finder.frontier_trace),
+        iteration_trace=tuple(finder.iteration_trace),
     )
 
 __all__ = [
@@ -62,6 +65,8 @@ __all__ = [
     "PathSeed",
     "Port",
     "FrontierPruneSample",
+    "IterationNetAttemptTrace",
+    "IterationTraceEntry",
     "RefinementOptions",
     "RoutingOptions",
     "RoutingProblem",

inire/model.py

@@ -107,6 +107,7 @@ class DiagnosticsOptions:
     capture_expanded: bool = False
     capture_conflict_trace: bool = False
     capture_frontier_trace: bool = False
+    capture_iteration_trace: bool = False
 
 
 @dataclass(frozen=True, slots=True)

inire/results.py

@@ -78,6 +78,33 @@ class NetFrontierTrace:
     samples: tuple[FrontierPruneSample, ...] = ()
 
 
+@dataclass(frozen=True, slots=True)
+class IterationNetAttemptTrace:
+    net_id: str
+    reached_target: bool
+    nodes_expanded: int
+    congestion_check_calls: int
+    pruned_closed_set: int
+    pruned_cost: int
+    pruned_hard_collision: int
+    guidance_seed_present: bool
+
+
+@dataclass(frozen=True, slots=True)
+class IterationTraceEntry:
+    iteration: int
+    congestion_penalty: float
+    routed_net_ids: tuple[str, ...]
+    completed_nets: int
+    conflict_edges: int
+    total_dynamic_collisions: int
+    nodes_expanded: int
+    congestion_check_calls: int
+    congestion_candidate_ids: int
+    congestion_exact_pair_checks: int
+    net_attempts: tuple[IterationNetAttemptTrace, ...] = ()
+
+
 @dataclass(frozen=True, slots=True)
 class RouteMetrics:
     nodes_expanded: int
@@ -231,3 +258,4 @@ class RoutingRunResult:
     expanded_nodes: tuple[tuple[int, int, int], ...] = ()
     conflict_trace: tuple[ConflictTraceEntry, ...] = ()
     frontier_trace: tuple[NetFrontierTrace, ...] = ()
+    iteration_trace: tuple[IterationTraceEntry, ...] = ()

inire/router/_router.py

@@ -11,6 +11,8 @@ from inire.results import (
     ComponentConflictTrace,
     ConflictTraceEntry,
     FrontierPruneSample,
+    IterationNetAttemptTrace,
+    IterationTraceEntry,
     NetConflictTrace,
     NetFrontierTrace,
     RoutingOutcome,
@@ -65,6 +67,22 @@ class _PairLocalTarget:
     net_ids: tuple[str, str]
 
 
+_ITERATION_TRACE_TOTALS = (
+    "nodes_expanded",
+    "congestion_check_calls",
+    "congestion_candidate_ids",
+    "congestion_exact_pair_checks",
+)
+
+_ATTEMPT_TRACE_TOTALS = (
+    "nodes_expanded",
+    "congestion_check_calls",
+    "pruned_closed_set",
+    "pruned_cost",
+    "pruned_hard_collision",
+)
+
+
 class PathFinder:
     __slots__ = (
         "context",
@@ -73,6 +91,7 @@ class PathFinder:
         "accumulated_expanded_nodes",
         "conflict_trace",
         "frontier_trace",
+        "iteration_trace",
     )
 
     def __init__(
@@ -90,6 +109,16 @@ class PathFinder:
         self.accumulated_expanded_nodes: list[tuple[int, int, int]] = []
         self.conflict_trace: list[ConflictTraceEntry] = []
         self.frontier_trace: list[NetFrontierTrace] = []
+        self.iteration_trace: list[IterationTraceEntry] = []
+
+    def _metric_total(self, metric_name: str) -> int:
+        return int(getattr(self.metrics, f"total_{metric_name}"))
+
+    def _capture_metric_totals(self, metric_names: tuple[str, ...]) -> dict[str, int]:
+        return {metric_name: self._metric_total(metric_name) for metric_name in metric_names}
+
+    def _metric_deltas(self, before: dict[str, int], after: dict[str, int]) -> dict[str, int]:
+        return {metric_name: after[metric_name] - before[metric_name] for metric_name in before}
 
     def _install_path(self, net_id: str, path: Sequence[ComponentResult]) -> None:
         all_geoms: list[Polygon] = []
@@ -749,13 +778,14 @@ class PathFinder:
         state: _RoutingState,
         iteration: int,
         net_id: str,
-    ) -> RoutingResult:
+    ) -> tuple[RoutingResult, bool]:
         search = self.context.options.search
         congestion = self.context.options.congestion
         diagnostics = self.context.options.diagnostics
         net = state.net_specs[net_id]
         self.metrics.total_nets_routed += 1
         self.context.cost_evaluator.collision_engine.remove_path(net_id)
+        guidance_seed_present = False
 
         if iteration == 0 and state.initial_paths and net_id in state.initial_paths:
             self.metrics.total_warm_start_paths_used += 1
@@ -774,6 +804,7 @@ class PathFinder:
                 if guidance_result and guidance_result.reached_target and guidance_result.path:
                     guidance_seed = guidance_result.as_seed().segments
                     guidance_bonus = max(10.0, self.context.options.objective.bend_penalty * 0.25)
+                    guidance_seed_present = True
 
             run_config = SearchRunConfig.from_options(
                 self.context.options,
@@ -800,7 +831,7 @@ class PathFinder:
                 state.accumulated_expanded_nodes.extend(self.metrics.last_expanded_nodes)
 
         if not path:
-            return RoutingResult(net_id=net_id, path=(), reached_target=False)
+            return RoutingResult(net_id=net_id, path=(), reached_target=False), guidance_seed_present
 
         reached_target = path[-1].end_port == net.target
         if reached_target:
@@ -812,11 +843,14 @@ class PathFinder:
             if report.self_collision_count > 0:
                 state.needs_self_collision_check.add(net_id)
 
-        return RoutingResult(
+        return (
+            RoutingResult(
                 net_id=net_id,
                 path=tuple(path),
                 reached_target=reached_target,
                 report=RoutingReport() if report is None else report,
+            ),
+            guidance_seed_present,
         )
 
     def _run_iteration(
@@ -827,24 +861,66 @@ class PathFinder:
         iteration_callback: Callable[[int, dict[str, RoutingResult]], None] | None,
     ) -> _IterationReview | None:
         congestion = self.context.options.congestion
+        diagnostics = self.context.options.diagnostics
         self.metrics.total_route_iterations += 1
         self.metrics.reset_per_route()
         if congestion.shuffle_nets and (iteration > 0 or state.initial_paths is None):
             iteration_seed = (congestion.seed + iteration) if congestion.seed is not None else None
             random.Random(iteration_seed).shuffle(state.ordered_net_ids)
 
+        iteration_penalty = self.context.congestion_penalty
         routed_net_ids = [net_id for net_id in state.ordered_net_ids if net_id in reroute_net_ids]
         self.metrics.total_nets_carried_forward += len(state.ordered_net_ids) - len(routed_net_ids)
+        iteration_before = {}
+        attempt_traces: list[IterationNetAttemptTrace] = []
+        if diagnostics.capture_iteration_trace:
+            iteration_before = self._capture_metric_totals(_ITERATION_TRACE_TOTALS)
 
         for net_id in routed_net_ids:
             if time.monotonic() - state.start_time > state.timeout_s:
                 self.metrics.total_timeout_events += 1
                 return None
 
-            result = self._route_net_once(state, iteration, net_id)
+            attempt_before = {}
+            if diagnostics.capture_iteration_trace:
+                attempt_before = self._capture_metric_totals(_ATTEMPT_TRACE_TOTALS)
+            result, guidance_seed_present = self._route_net_once(state, iteration, net_id)
             state.results[net_id] = result
+            if diagnostics.capture_iteration_trace:
+                attempt_after = self._capture_metric_totals(_ATTEMPT_TRACE_TOTALS)
+                deltas = self._metric_deltas(attempt_before, attempt_after)
+                attempt_traces.append(
+                    IterationNetAttemptTrace(
+                        net_id=net_id,
+                        reached_target=result.reached_target,
+                        nodes_expanded=deltas["nodes_expanded"],
+                        congestion_check_calls=deltas["congestion_check_calls"],
+                        pruned_closed_set=deltas["pruned_closed_set"],
+                        pruned_cost=deltas["pruned_cost"],
+                        pruned_hard_collision=deltas["pruned_hard_collision"],
+                        guidance_seed_present=guidance_seed_present,
+                    )
+                )
 
         review = self._reverify_iteration_results(state)
+        if diagnostics.capture_iteration_trace:
+            iteration_after = self._capture_metric_totals(_ITERATION_TRACE_TOTALS)
+            deltas = self._metric_deltas(iteration_before, iteration_after)
+            self.iteration_trace.append(
+                IterationTraceEntry(
+                    iteration=iteration,
+                    congestion_penalty=iteration_penalty,
+                    routed_net_ids=tuple(routed_net_ids),
+                    completed_nets=len(review.completed_net_ids),
+                    conflict_edges=len(review.conflict_edges),
+                    total_dynamic_collisions=review.total_dynamic_collisions,
+                    nodes_expanded=deltas["nodes_expanded"],
+                    congestion_check_calls=deltas["congestion_check_calls"],
+                    congestion_candidate_ids=deltas["congestion_candidate_ids"],
+                    congestion_exact_pair_checks=deltas["congestion_exact_pair_checks"],
+                    net_attempts=tuple(attempt_traces),
+                )
+            )
 
         if iteration_callback:
             iteration_callback(iteration, state.results)
@@ -973,6 +1049,7 @@ class PathFinder:
         self.accumulated_expanded_nodes = []
         self.conflict_trace = []
         self.frontier_trace = []
+        self.iteration_trace = []
         self.metrics.reset_totals()
         self.metrics.reset_per_route()
 

inire/tests/example_scenarios.py

@@ -91,6 +91,7 @@ def _make_run_result(
         expanded_nodes=tuple(pathfinder.accumulated_expanded_nodes),
         conflict_trace=tuple(pathfinder.conflict_trace),
         frontier_trace=tuple(pathfinder.frontier_trace),
+        iteration_trace=tuple(pathfinder.iteration_trace),
     )
 
 
@@ -424,6 +425,14 @@ def snapshot_example_07_no_warm_start() -> ScenarioSnapshot:
     )
 
 
+def snapshot_example_07_no_warm_start_seed43() -> ScenarioSnapshot:
+    return _snapshot_example_07_variant(
+        "example_07_large_scale_routing_no_warm_start_seed43",
+        warm_start_enabled=False,
+        seed=43,
+    )
+
+
 def trace_example_07() -> RoutingRunResult:
     return _trace_example_07_variant(warm_start_enabled=True)
 
@@ -432,6 +441,10 @@ def trace_example_07_no_warm_start() -> RoutingRunResult:
     return _trace_example_07_variant(warm_start_enabled=False)
 
 
+def trace_example_07_no_warm_start_seed43() -> RoutingRunResult:
+    return _trace_example_07_variant(warm_start_enabled=False, seed=43)
+
+
 def _build_example_07_variant_stack(
     *,
     num_nets: int,
@@ -439,6 +452,7 @@ def _build_example_07_variant_stack(
     warm_start_enabled: bool,
     capture_conflict_trace: bool = False,
     capture_frontier_trace: bool = False,
+    capture_iteration_trace: bool = False,
 ) -> tuple[CostEvaluator, AStarMetrics, PathFinder]:
     bounds = (0, 0, 1000, 1000)
     obstacles = [
@@ -481,6 +495,7 @@ def _build_example_07_variant_stack(
             "capture_expanded": True,
             "capture_conflict_trace": capture_conflict_trace,
             "capture_frontier_trace": capture_frontier_trace,
+            "capture_iteration_trace": capture_iteration_trace,
             "shuffle_nets": True,
             "seed": seed,
             "warm_start_enabled": warm_start_enabled,
@@ -496,6 +511,7 @@ def _run_example_07_variant(
     warm_start_enabled: bool,
     capture_conflict_trace: bool = False,
     capture_frontier_trace: bool = False,
+    capture_iteration_trace: bool = False,
 ) -> RoutingRunResult:
     evaluator, metrics, pathfinder = _build_example_07_variant_stack(
         num_nets=num_nets,
@@ -503,6 +519,7 @@ def _run_example_07_variant(
         warm_start_enabled=warm_start_enabled,
         capture_conflict_trace=capture_conflict_trace,
         capture_frontier_trace=capture_frontier_trace,
+        capture_iteration_trace=capture_iteration_trace,
     )
 
     def iteration_callback(idx: int, current_results: dict[str, RoutingResult]) -> None:
@@ -519,11 +536,12 @@ def _snapshot_example_07_variant(
     name: str,
     *,
     warm_start_enabled: bool,
+    seed: int = 42,
 ) -> ScenarioSnapshot:
     t0 = perf_counter()
     run = _run_example_07_variant(
         num_nets=10,
-        seed=42,
+        seed=seed,
         warm_start_enabled=warm_start_enabled,
     )
     t1 = perf_counter()
@@ -533,13 +551,15 @@ def _snapshot_example_07_variant(
 def _trace_example_07_variant(
     *,
     warm_start_enabled: bool,
+    seed: int = 42,
 ) -> RoutingRunResult:
     return _run_example_07_variant(
         num_nets=10,
-        seed=42,
+        seed=seed,
         warm_start_enabled=warm_start_enabled,
         capture_conflict_trace=True,
         capture_frontier_trace=True,
+        capture_iteration_trace=True,
     )
 
 
@@ -644,6 +664,7 @@ SCENARIO_SNAPSHOTS: tuple[tuple[str, ScenarioSnapshotRun], ...] = (
 
 PERFORMANCE_SCENARIO_SNAPSHOTS: tuple[tuple[str, ScenarioSnapshotRun], ...] = (
     ("example_07_large_scale_routing_no_warm_start", snapshot_example_07_no_warm_start),
+    ("example_07_large_scale_routing_no_warm_start_seed43", snapshot_example_07_no_warm_start_seed43),
 )
 
 TRACE_SCENARIO_RUNS: tuple[tuple[str, TraceScenarioRun], ...] = (
@@ -653,6 +674,7 @@ TRACE_SCENARIO_RUNS: tuple[tuple[str, TraceScenarioRun], ...] = (
 
 TRACE_PERFORMANCE_SCENARIO_RUNS: tuple[tuple[str, TraceScenarioRun], ...] = (
     ("example_07_large_scale_routing_no_warm_start", trace_example_07_no_warm_start),
+    ("example_07_large_scale_routing_no_warm_start_seed43", trace_example_07_no_warm_start_seed43),
 )
 
 

inire/tests/test_api.py

@@ -54,6 +54,7 @@ def test_route_problem_smoke() -> None:
     assert run.results_by_net["net1"].is_valid
     assert run.conflict_trace == ()
     assert run.frontier_trace == ()
+    assert run.iteration_trace == ()
 
 
 def test_route_problem_supports_configs_and_debug_data() -> None:
@@ -182,6 +183,72 @@ def test_capture_conflict_trace_preserves_route_outputs() -> None:
     assert [entry.stage for entry in run_with_trace.conflict_trace] == ["iteration", "restored_best", "final"]
 
 
+def test_capture_iteration_trace_preserves_route_outputs() -> None:
+    problem = RoutingProblem(
+        bounds=(0, 0, 100, 100),
+        nets=(
+            NetSpec("horizontal", Port(10, 50, 0), Port(90, 50, 0), width=2.0),
+            NetSpec("vertical", Port(50, 10, 90), Port(50, 90, 90), width=2.0),
+        ),
+    )
+    base_options = RoutingOptions(
+        congestion=CongestionOptions(max_iterations=1, warm_start_enabled=False),
+        refinement=RefinementOptions(enabled=False),
+    )
+
+    run_without_trace = route(problem, options=base_options)
+    run_with_trace = route(
+        problem,
+        options=RoutingOptions(
+            congestion=base_options.congestion,
+            refinement=base_options.refinement,
+            diagnostics=DiagnosticsOptions(capture_iteration_trace=True),
+        ),
+    )
+
+    assert {net_id: result.outcome for net_id, result in run_without_trace.results_by_net.items()} == {
+        net_id: result.outcome for net_id, result in run_with_trace.results_by_net.items()
+    }
+    assert len(run_with_trace.iteration_trace) == 1
+
+
+def test_capture_iteration_trace_records_iteration_and_attempt_deltas() -> None:
+    problem = RoutingProblem(
+        bounds=(0, 0, 100, 100),
+        nets=(
+            NetSpec("horizontal", Port(10, 50, 0), Port(90, 50, 0), width=2.0),
+            NetSpec("vertical", Port(50, 10, 90), Port(50, 90, 90), width=2.0),
+        ),
+    )
+    run = route(
+        problem,
+        options=RoutingOptions(
+            congestion=CongestionOptions(max_iterations=1, warm_start_enabled=False),
+            refinement=RefinementOptions(enabled=False),
+            diagnostics=DiagnosticsOptions(capture_iteration_trace=True),
+        ),
+    )
+
+    entry = run.iteration_trace[0]
+    assert entry.iteration == 0
+    assert entry.congestion_penalty == 100.0
+    assert entry.routed_net_ids == ("horizontal", "vertical")
+    assert entry.completed_nets == 0
+    assert entry.conflict_edges == 1
+    assert entry.total_dynamic_collisions >= 2
+    assert entry.nodes_expanded >= 0
+    assert entry.congestion_check_calls >= 0
+    assert entry.congestion_candidate_ids >= 0
+    assert entry.congestion_exact_pair_checks >= 0
+    assert len(entry.net_attempts) == 2
+    assert [attempt.net_id for attempt in entry.net_attempts] == ["horizontal", "vertical"]
+    assert all(attempt.nodes_expanded >= 0 for attempt in entry.net_attempts)
+    assert all(attempt.congestion_check_calls >= 0 for attempt in entry.net_attempts)
+    assert all(not attempt.guidance_seed_present for attempt in entry.net_attempts)
+    assert sum(attempt.nodes_expanded for attempt in entry.net_attempts) == entry.nodes_expanded
+    assert sum(attempt.congestion_check_calls for attempt in entry.net_attempts) == entry.congestion_check_calls
+
+
 def test_capture_conflict_trace_records_component_pairs() -> None:
     problem = RoutingProblem(
         bounds=(0, 0, 100, 100),

inire/tests/test_example_performance.py

@@ -6,7 +6,13 @@ from typing import TYPE_CHECKING
 
 import pytest
 
-from inire.tests.example_scenarios import SCENARIOS, ScenarioOutcome, snapshot_example_07_no_warm_start
+from inire.tests.example_scenarios import (
+    SCENARIOS,
+    ScenarioOutcome,
+    snapshot_example_07_no_warm_start,
+    snapshot_example_07_no_warm_start_seed43,
+    trace_example_07_no_warm_start_seed43,
+)
 
 if TYPE_CHECKING:
     from collections.abc import Callable
@@ -16,6 +22,7 @@ RUN_PERFORMANCE = os.environ.get("INIRE_RUN_PERFORMANCE") == "1"
 PERFORMANCE_REPEATS = 3
 REGRESSION_FACTOR = 1.5
 NO_WARM_START_REGRESSION_SECONDS = 15.0
+NO_WARM_START_SEED43_REGRESSION_SECONDS = 120.0
 
 # Baselines are measured from clean 6a28dcf-style runs without plotting.
 BASELINE_SECONDS = {
@@ -85,3 +92,32 @@ def test_example_07_no_warm_start_runtime_regression() -> None:
         f"{snapshot.duration_s:.4f}s exceeded guardrail "
         f"{NO_WARM_START_REGRESSION_SECONDS:.1f}s"
     )
+
+
+@pytest.mark.performance
+@pytest.mark.skipif(not RUN_PERFORMANCE, reason="set INIRE_RUN_PERFORMANCE=1 to run runtime regression checks")
+def test_example_07_no_warm_start_seed43_runtime_regression() -> None:
+    snapshot = snapshot_example_07_no_warm_start_seed43()
+    run = trace_example_07_no_warm_start_seed43()
+
+    assert snapshot.total_results == 10
+    assert snapshot.valid_results == 10
+    assert snapshot.reached_targets == 10
+    assert snapshot.metrics.warm_start_paths_built == 0
+    assert snapshot.metrics.warm_start_paths_used == 0
+    assert snapshot.metrics.pair_local_search_pairs_considered >= 1
+    assert snapshot.metrics.pair_local_search_accepts >= 1
+    assert snapshot.duration_s <= NO_WARM_START_SEED43_REGRESSION_SECONDS, (
+        "example_07_large_scale_routing_no_warm_start_seed43 runtime "
+        f"{snapshot.duration_s:.4f}s exceeded guardrail "
+        f"{NO_WARM_START_SEED43_REGRESSION_SECONDS:.1f}s"
+    )
+
+    assert run.iteration_trace
+    assert len(run.results_by_net) == 10
+    assert sum(result.is_valid for result in run.results_by_net.values()) == 10
+    assert sum(result.reached_target for result in run.results_by_net.values()) == 10
+    assert run.metrics.warm_start_paths_built == 0
+    assert run.metrics.warm_start_paths_used == 0
+    assert run.metrics.pair_local_search_pairs_considered >= 1
+    assert run.metrics.pair_local_search_accepts >= 1

inire/tests/test_performance_reporting.py

@@ -276,6 +276,30 @@ def test_record_frontier_trace_script_writes_selected_scenario(tmp_path: Path) -
     assert (tmp_path / "frontier_trace.md").exists()
 
 
+def test_record_iteration_trace_script_writes_selected_scenario(tmp_path: Path) -> None:
+    repo_root = Path(__file__).resolve().parents[2]
+    script_path = repo_root / "scripts" / "record_iteration_trace.py"
+
+    subprocess.run(
+        [
+            sys.executable,
+            str(script_path),
+            "--include-performance-only",
+            "--scenario",
+            "example_07_large_scale_routing_no_warm_start",
+            "--output-dir",
+            str(tmp_path),
+        ],
+        check=True,
+    )
+
+    payload = json.loads((tmp_path / "iteration_trace.json").read_text())
+    assert payload["generated_at"]
+    assert payload["generator"] == "scripts/record_iteration_trace.py"
+    assert [entry["name"] for entry in payload["scenarios"]] == ["example_07_large_scale_routing_no_warm_start"]
+    assert (tmp_path / "iteration_trace.md").exists()
+
+
 def test_characterize_pair_local_search_script_writes_outputs(tmp_path: Path) -> None:
     repo_root = Path(__file__).resolve().parents[2]
     script_path = repo_root / "scripts" / "characterize_pair_local_search.py"

scripts/record_iteration_trace.py

@@ -0,0 +1,186 @@
+#!/usr/bin/env python3
+from __future__ import annotations
+
+import argparse
+import json
+from collections import Counter
+from dataclasses import asdict
+from datetime import datetime
+from pathlib import Path
+
+from inire.tests.example_scenarios import TRACE_PERFORMANCE_SCENARIO_RUNS, TRACE_SCENARIO_RUNS
+
+
+def _trace_registry(include_performance_only: bool) -> tuple[tuple[str, object], ...]:
+    if include_performance_only:
+        return TRACE_SCENARIO_RUNS + TRACE_PERFORMANCE_SCENARIO_RUNS
+    return TRACE_SCENARIO_RUNS
+
+
+def _selected_runs(
+    selected_scenarios: tuple[str, ...] | None,
+    *,
+    include_performance_only: bool,
+) -> tuple[tuple[str, object], ...]:
+    if selected_scenarios is None:
+        perf_registry = dict(TRACE_PERFORMANCE_SCENARIO_RUNS)
+        return (
+            (
+                "example_07_large_scale_routing_no_warm_start",
+                perf_registry["example_07_large_scale_routing_no_warm_start"],
+            ),
+            (
+                "example_07_large_scale_routing_no_warm_start_seed43",
+                perf_registry["example_07_large_scale_routing_no_warm_start_seed43"],
+            ),
+        )
+
+    registry = dict(TRACE_SCENARIO_RUNS + TRACE_PERFORMANCE_SCENARIO_RUNS)
+    allowed_standard = dict(_trace_registry(include_performance_only))
+    runs = []
+    for name in selected_scenarios:
+        if name in allowed_standard:
+            runs.append((name, allowed_standard[name]))
+            continue
+        if name in registry:
+            runs.append((name, registry[name]))
+            continue
+        valid = ", ".join(sorted(registry))
+        raise SystemExit(f"Unknown iteration-trace scenario: {name}. Valid scenarios: {valid}")
+    return tuple(runs)
+
+
+def _build_payload(
+    selected_scenarios: tuple[str, ...] | None,
+    *,
+    include_performance_only: bool,
+) -> dict[str, object]:
+    scenarios = []
+    for name, run in _selected_runs(selected_scenarios, include_performance_only=include_performance_only):
+        result = run()
+        scenarios.append(
+            {
+                "name": name,
+                "summary": {
+                    "total_results": len(result.results_by_net),
+                    "valid_results": sum(1 for entry in result.results_by_net.values() if entry.is_valid),
+                    "reached_targets": sum(1 for entry in result.results_by_net.values() if entry.reached_target),
+                },
+                "metrics": asdict(result.metrics),
+                "iteration_trace": [asdict(entry) for entry in result.iteration_trace],
+            }
+        )
+    return {
+        "generated_at": datetime.now().astimezone().isoformat(timespec="seconds"),
+        "generator": "scripts/record_iteration_trace.py",
+        "scenarios": scenarios,
+    }
+
+
+def _render_markdown(payload: dict[str, object]) -> str:
+    lines = [
+        "# Iteration Trace",
+        "",
+        f"Generated at {payload['generated_at']} by `{payload['generator']}`.",
+        "",
+    ]
+
+    for scenario in payload["scenarios"]:
+        lines.extend(
+            [
+                f"## {scenario['name']}",
+                "",
+                f"Results: {scenario['summary']['valid_results']} valid / "
+                f"{scenario['summary']['reached_targets']} reached / "
+                f"{scenario['summary']['total_results']} total.",
+                "",
+                "| Iteration | Penalty | Routed Nets | Completed | Conflict Edges | Dynamic Collisions | Nodes | Congestion Checks | Candidate Ids | Exact Pairs |",
+                "| --: | --: | --: | --: | --: | --: | --: | --: | --: | --: |",
+            ]
+        )
+
+        net_node_counts: Counter[str] = Counter()
+        net_check_counts: Counter[str] = Counter()
+        for entry in scenario["iteration_trace"]:
+            lines.append(
+                "| "
+                f"{entry['iteration']} | "
+                f"{entry['congestion_penalty']:.1f} | "
+                f"{len(entry['routed_net_ids'])} | "
+                f"{entry['completed_nets']} | "
+                f"{entry['conflict_edges']} | "
+                f"{entry['total_dynamic_collisions']} | "
+                f"{entry['nodes_expanded']} | "
+                f"{entry['congestion_check_calls']} | "
+                f"{entry['congestion_candidate_ids']} | "
+                f"{entry['congestion_exact_pair_checks']} |"
+            )
+            for attempt in entry["net_attempts"]:
+                net_node_counts[attempt["net_id"]] += attempt["nodes_expanded"]
+                net_check_counts[attempt["net_id"]] += attempt["congestion_check_calls"]
+
+        lines.extend(["", "Top nets by iteration-attributed nodes expanded:", ""])
+        if net_node_counts:
+            for net_id, count in net_node_counts.most_common(10):
+                lines.append(f"- `{net_id}`: {count}")
+        else:
+            lines.append("- None")
+
+        lines.extend(["", "Top nets by iteration-attributed congestion checks:", ""])
+        if net_check_counts:
+            for net_id, count in net_check_counts.most_common(10):
+                lines.append(f"- `{net_id}`: {count}")
+        else:
+            lines.append("- None")
+
+        lines.append("")
+
+    return "\n".join(lines)
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description="Record iteration-trace artifacts for selected trace scenarios.")
+    parser.add_argument(
+        "--scenario",
+        action="append",
+        dest="scenarios",
+        default=[],
+        help="Optional trace scenario name to include. May be passed more than once.",
+    )
+    parser.add_argument(
+        "--include-performance-only",
+        action="store_true",
+        help="Include performance-only trace scenarios when selecting from the standard registry.",
+    )
+    parser.add_argument(
+        "--output-dir",
+        type=Path,
+        default=None,
+        help="Directory to write iteration_trace.json and iteration_trace.md into. Defaults to <repo>/docs.",
+    )
+    args = parser.parse_args()
+
+    repo_root = Path(__file__).resolve().parents[1]
+    output_dir = repo_root / "docs" if args.output_dir is None else args.output_dir.resolve()
+    output_dir.mkdir(exist_ok=True)
+
+    selected = tuple(args.scenarios) if args.scenarios else None
+    payload = _build_payload(selected, include_performance_only=args.include_performance_only)
+    json_path = output_dir / "iteration_trace.json"
+    markdown_path = output_dir / "iteration_trace.md"
+
+    json_path.write_text(json.dumps(payload, indent=2, sort_keys=True) + "\n")
+    markdown_path.write_text(_render_markdown(payload) + "\n")
+
+    if json_path.is_relative_to(repo_root):
+        print(f"Wrote {json_path.relative_to(repo_root)}")
+    else:
+        print(f"Wrote {json_path}")
+    if markdown_path.is_relative_to(repo_root):
+        print(f"Wrote {markdown_path.relative_to(repo_root)}")
+    else:
+        print(f"Wrote {markdown_path}")
+
+
+if __name__ == "__main__":
+    main()