diff --git a/src/renderer/src/components/automations/automation-host-catalog-generation.test.ts b/src/renderer/src/components/automations/automation-host-catalog-generation.test.ts
index f085311fda2..c95384d750b 100644
--- a/src/renderer/src/components/automations/automation-host-catalog-generation.test.ts
+++ b/src/renderer/src/components/automations/automation-host-catalog-generation.test.ts
@@ -67,6 +67,14 @@ describe('automation catalog generation', () => {
     expect(registry.get(ENV_B)).toBe(1)
   })
 
+  it('bounds authority generations without reopening an evicted fence', () => {
+    const authorities = Array.from({ length: 600 }, (_, index) => runtime(`env-${index}`))
+    registry.sync(buildAutomationHostCatalog(input({ runtimes: authorities })))
+
+    expect(registry.get({ kind: 'runtime', environmentId: 'env-0' })).toBeGreaterThan(1)
+    expect(registry.get({ kind: 'runtime', environmentId: 'env-599' })).toBe(1)
+  })
+
   it('advances only the authority whose target bucket hydrated', () => {
     registry.sync(
       buildAutomationHostCatalog(
diff --git a/src/renderer/src/components/automations/automation-host-catalog-generation.ts b/src/renderer/src/components/automations/automation-host-catalog-generation.ts
index 8db2c85c16c..3de17481787 100644
--- a/src/renderer/src/components/automations/automation-host-catalog-generation.ts
+++ b/src/renderer/src/components/automations/automation-host-catalog-generation.ts
@@ -38,6 +38,8 @@ export type AutomationCatalogGenerationRegistry = {
   reset: () => void
 }
 
+const AUTOMATION_AUTHORITY_GENERATION_MAX_ENTRIES = 512
+
 // Health is deliberately absent: only membership and incarnation belong here.
 export function automationHostCatalogEntryFingerprint(entry: AutomationHostCatalogEntry): string {
   return `${entry.stableKey}|${entry.catalogState}|${entry.owner ? ownerKey(entry.owner) : '-'}`
@@ -62,6 +64,29 @@ export function createAutomationCatalogGenerationRegistry(): AutomationCatalogGe
   const generationByAuthorityKey = new Map<string, number>()
   const fingerprintByAuthorityKey = new Map<string, string>()
   const ownerKeyByStableKey = new Map<string, string>()
+  const evictedAuthorityKeys = new Set<string>()
+  let generationFloor = 0
+
+  const trimAuthorityGenerations = (): void => {
+    while (generationByAuthorityKey.size > AUTOMATION_AUTHORITY_GENERATION_MAX_ENTRIES) {
+      const oldest = generationByAuthorityKey.keys().next()
+      if (oldest.done) {
+        break
+      }
+      const key = oldest.value
+      generationByAuthorityKey.delete(key)
+      fingerprintByAuthorityKey.delete(key)
+      evictedAuthorityKeys.delete(key)
+      evictedAuthorityKeys.add(key)
+    }
+    while (evictedAuthorityKeys.size > AUTOMATION_AUTHORITY_GENERATION_MAX_ENTRIES) {
+      const oldest = evictedAuthorityKeys.keys().next()
+      if (oldest.done) {
+        break
+      }
+      evictedAuthorityKeys.delete(oldest.value)
+    }
+  }
 
   /** Compared only where an owner exists: a disconnect can strip owner refs, and that is not a new incarnation. */
   const reincarnations = (catalog: AutomationHostCatalog): string[] => {
@@ -90,14 +115,28 @@ export function createAutomationCatalogGenerationRegistry(): AutomationCatalogGe
 
   const advance = (authorityKey: string, fingerprint: string): void => {
     fingerprintByAuthorityKey.set(authorityKey, fingerprint)
-    generationByAuthorityKey.set(
-      authorityKey,
-      (generationByAuthorityKey.get(authorityKey) ?? 0) + 1
-    )
+    const previous = generationByAuthorityKey.get(authorityKey)
+    const next =
+      previous !== undefined
+        ? previous + 1
+        : evictedAuthorityKeys.has(authorityKey)
+          ? generationFloor + 1
+          : 1
+    generationFloor = next
+    evictedAuthorityKeys.delete(authorityKey)
+    generationByAuthorityKey.set(authorityKey, next)
+    trimAuthorityGenerations()
   }
 
   return {
-    get: (authority) => generationByAuthorityKey.get(automationAuthorityCatalogKey(authority)) ?? 0,
+    get: (authority) => {
+      const key = automationAuthorityCatalogKey(authority)
+      const generation = generationByAuthorityKey.get(key)
+      if (generation !== undefined) {
+        return generation
+      }
+      return evictedAuthorityKeys.has(key) ? generationFloor + 1 : 0
+    },
     sync: (catalog) => {
       const reincarnatedStableKeys = reincarnations(catalog)
       const next = fingerprintByAuthority(catalog)
@@ -121,6 +160,8 @@ export function createAutomationCatalogGenerationRegistry(): AutomationCatalogGe
       generationByAuthorityKey.clear()
       fingerprintByAuthorityKey.clear()
       ownerKeyByStableKey.clear()
+      evictedAuthorityKeys.clear()
+      generationFloor = 0
     }
   }
 }