From f091817c9a78b3df5cf626b8a2577daba9987500 Mon Sep 17 00:00:00 2001
From: Ahmed Alshaybani <shibosoftwaredev@gmail.com>
Date: Thu, 5 Nov 2026 23:05:41 +0100
Subject: [PATCH 1/2] Expand each region once during static reachability checks

---
 lib/static-reachability.ts | 27 ++++++++++-----------------
 1 file changed, 10 insertions(+), 17 deletions(-)

diff --git a/lib/static-reachability.ts b/lib/static-reachability.ts
index 91583446..c98d3097 100644
--- a/lib/static-reachability.ts
+++ b/lib/static-reachability.ts
@@ -122,31 +122,27 @@ const hasStaticReachabilityPath = (
     return false
   }
 
-  const queue: Array<{ portId: PortId; nextRegionId: RegionId }> = [
-    {
-      portId: startPortId,
-      nextRegionId: startRegionId,
-    },
-  ]
+  const queue: RegionId[] = [startRegionId]
+  const seenRegions = new Set(queue)
   const seenHops = new Set<number>([
     startPortId * topology.regionCount + startRegionId,
   ])
 
   for (let queueIndex = 0; queueIndex < queue.length; queueIndex++) {
-    const currentCandidate = queue[queueIndex]!
+    const currentRegionId = queue[queueIndex]!
 
     if (
       isRegionBlockedForStaticReachability(
         problem,
         routeNetId,
-        currentCandidate.nextRegionId,
+        currentRegionId,
       )
     ) {
       continue
     }
 
     for (const neighborPortId of topology.regionIncidentPorts[
-      currentCandidate.nextRegionId
+      currentRegionId
     ] ?? []) {
       const assignedNetId = portAssignment[neighborPortId]
 
@@ -165,9 +161,6 @@ const hasStaticReachabilityPath = (
         }
         return true
       }
-      if (neighborPortId === currentCandidate.portId) {
-        continue
-      }
       if (assignedNetId !== -1 && assignedNetId !== routeNetId) {
         continue
       }
@@ -177,7 +170,7 @@ const hasStaticReachabilityPath = (
 
       const incidentRegions = topology.incidentPortRegion[neighborPortId] ?? []
       const nextRegionId =
-        incidentRegions[0] === currentCandidate.nextRegionId
+        incidentRegions[0] === currentRegionId
           ? incidentRegions[1]
           : incidentRegions[0]
 
@@ -197,10 +190,10 @@ const hasStaticReachabilityPath = (
       }
 
       seenHops.add(hopId)
-      queue.push({
-        portId: neighborPortId,
-        nextRegionId,
-      })
+      if (!seenRegions.has(nextRegionId)) {
+        seenRegions.add(nextRegionId)
+        queue.push(nextRegionId)
+      }
     }
   }
 

From f21e8c7937d416d98180586711decd2468fc2611 Mon Sep 17 00:00:00 2001
From: Ahmed Alshaybani <shibosoftwaredev@gmail.com>
Date: Thu, 5 Nov 2026 23:08:51 +0100
Subject: [PATCH 2/2] Keep bounded reachability behavior unchanged

---
 lib/static-reachability.ts | 34 ++++++++++++++++++++++++----------
 1 file changed, 24 insertions(+), 10 deletions(-)

diff --git a/lib/static-reachability.ts b/lib/static-reachability.ts
index c98d3097..42e3aec8 100644
--- a/lib/static-reachability.ts
+++ b/lib/static-reachability.ts
@@ -122,27 +122,38 @@ const hasStaticReachabilityPath = (
     return false
   }
 
-  const queue: RegionId[] = [startRegionId]
-  const seenRegions = new Set(queue)
+  const queue: Array<{ portId: PortId; nextRegionId: RegionId }> = [
+    {
+      portId: startPortId,
+      nextRegionId: startRegionId,
+    },
+  ]
   const seenHops = new Set<number>([
     startPortId * topology.regionCount + startRegionId,
   ])
+  const expandedRegions = new Set<RegionId>()
 
   for (let queueIndex = 0; queueIndex < queue.length; queueIndex++) {
-    const currentRegionId = queue[queueIndex]!
+    const currentCandidate = queue[queueIndex]!
+    if (maxPrecheckHops === Number.POSITIVE_INFINITY) {
+      if (expandedRegions.has(currentCandidate.nextRegionId)) {
+        continue
+      }
+      expandedRegions.add(currentCandidate.nextRegionId)
+    }
 
     if (
       isRegionBlockedForStaticReachability(
         problem,
         routeNetId,
-        currentRegionId,
+        currentCandidate.nextRegionId,
       )
     ) {
       continue
     }
 
     for (const neighborPortId of topology.regionIncidentPorts[
-      currentRegionId
+      currentCandidate.nextRegionId
     ] ?? []) {
       const assignedNetId = portAssignment[neighborPortId]
 
@@ -161,6 +172,9 @@ const hasStaticReachabilityPath = (
         }
         return true
       }
+      if (neighborPortId === currentCandidate.portId) {
+        continue
+      }
       if (assignedNetId !== -1 && assignedNetId !== routeNetId) {
         continue
       }
@@ -170,7 +184,7 @@ const hasStaticReachabilityPath = (
 
       const incidentRegions = topology.incidentPortRegion[neighborPortId] ?? []
       const nextRegionId =
-        incidentRegions[0] === currentRegionId
+        incidentRegions[0] === currentCandidate.nextRegionId
           ? incidentRegions[1]
           : incidentRegions[0]
 
@@ -190,10 +204,10 @@ const hasStaticReachabilityPath = (
       }
 
       seenHops.add(hopId)
-      if (!seenRegions.has(nextRegionId)) {
-        seenRegions.add(nextRegionId)
-        queue.push(nextRegionId)
-      }
+      queue.push({
+        portId: neighborPortId,
+        nextRegionId,
+      })
     }
   }