diff --git a/src/renderer/src/lib/setup-script-prompt.test.ts b/src/renderer/src/lib/setup-script-prompt.test.ts
index 70d226bc0cf..605142bc154 100644
--- a/src/renderer/src/lib/setup-script-prompt.test.ts
+++ b/src/renderer/src/lib/setup-script-prompt.test.ts
@@ -202,6 +202,59 @@ describe('setup script prompt inspection', () => {
     ).toEqual([getSetupScriptPromptDismissalKey(localIdentity)])
   })
 
+  it('reuses the input array when it is empty', () => {
+    const input: string[] = []
+    expect(
+      filterSetupScriptPromptDismissalsToValidRepos(
+        input,
+        new Set([getRepoHostIdentityForParts('repo-1', 'local')])
+      )
+    ).toBe(input)
+  })
+
+  it('reuses the input array when every dismissal is already a valid host-identity key', () => {
+    const localIdentity = getRepoHostIdentityForParts('repo-1', 'local')
+    const remoteIdentity = getRepoHostIdentityForParts('repo-2', 'ssh:host-a')
+    const input = [
+      getSetupScriptPromptDismissalKey(localIdentity),
+      getSetupScriptPromptDismissalKey(remoteIdentity)
+    ]
+    expect(
+      filterSetupScriptPromptDismissalsToValidRepos(
+        input,
+        new Set([localIdentity, remoteIdentity])
+      )
+    ).toBe(input)
+  })
+
+  it('allocates when a legacy repo-id dismissal is rewritten to a host identity', () => {
+    const localIdentity = getRepoHostIdentityForParts('repo-1', 'local')
+    const input = [getSetupScriptPromptDismissalKey('repo-1')]
+    const result = filterSetupScriptPromptDismissalsToValidRepos(input, new Set([localIdentity]))
+    expect(result).not.toBe(input)
+    expect(result).toEqual([getSetupScriptPromptDismissalKey(localIdentity)])
+  })
+
+  it('allocates when a stale dismissal is dropped', () => {
+    const localIdentity = getRepoHostIdentityForParts('repo-1', 'local')
+    const input = [
+      getSetupScriptPromptDismissalKey(localIdentity),
+      getSetupScriptPromptDismissalKey(getRepoHostIdentityForParts('gone', 'local'))
+    ]
+    const result = filterSetupScriptPromptDismissalsToValidRepos(input, new Set([localIdentity]))
+    expect(result).not.toBe(input)
+    expect(result).toEqual([getSetupScriptPromptDismissalKey(localIdentity)])
+  })
+
+  it('allocates when a duplicate valid dismissal is deduped', () => {
+    const localIdentity = getRepoHostIdentityForParts('repo-1', 'local')
+    const key = getSetupScriptPromptDismissalKey(localIdentity)
+    const input = [key, key]
+    const result = filterSetupScriptPromptDismissalsToValidRepos(input, new Set([localIdentity]))
+    expect(result).not.toBe(input)
+    expect(result).toEqual([key])
+  })
+
   it('drops a legacy repo-id dismissal when that id exists on multiple hosts', () => {
     const localIdentity = getRepoHostIdentityForParts('repo-1', 'local')
     const remoteIdentity = getRepoHostIdentityForParts('repo-1', 'runtime:windows')
diff --git a/src/renderer/src/lib/setup-script-prompt.ts b/src/renderer/src/lib/setup-script-prompt.ts
index 8bf56d13980..6adbc04b092 100644
--- a/src/renderer/src/lib/setup-script-prompt.ts
+++ b/src/renderer/src/lib/setup-script-prompt.ts
@@ -90,10 +90,21 @@ export function isSetupScriptPromptDismissed(
   return dismissedEntries.includes(getSetupScriptPromptDismissalKey(repoHostIdentity))
 }
 
+function isUnchangedDismissalList(
+  value: unknown,
+  next: readonly string[]
+): value is readonly string[] {
+  return (
+    Array.isArray(value) &&
+    value.length === next.length &&
+    value.every((entry, index) => entry === next[index])
+  )
+}
+
 export function filterSetupScriptPromptDismissalsToValidRepos(
   value: unknown,
   validRepoHostIdentities: Set<string>
-): string[] {
+): readonly string[] {
   const unambiguousIdentityByRepoId = new Map<string, string | null>()
   for (const identity of validRepoHostIdentities) {
     const separatorIndex = identity.indexOf('\0')
@@ -117,10 +128,18 @@ export function filterSetupScriptPromptDismissalsToValidRepos(
       }
     }
   }
+  // Why: fetchRepos / fetchRuntimeEnvironmentRepos / validateRepoScopedUi assign
+  // this into set() on every catalog refresh. SetupScriptPromptCard Object.is-
+  // subscribes to the array, so a fresh copy on a no-op prune is a guaranteed miss.
+  // Compare against the original input, not the sanitize copy — sanitize always
+  // allocates, including for [] and already-valid host-identity keys.
+  if (isUnchangedDismissalList(value, next)) {
+    return value
+  }
   return next
 }
 
-export function sanitizeSetupScriptPromptDismissals(value: unknown): string[] {
+export function sanitizeSetupScriptPromptDismissals(value: unknown): readonly string[] {
   if (!Array.isArray(value)) {
     return []
   }
diff --git a/src/renderer/src/store/slices/repos-refresh-identity.test.ts b/src/renderer/src/store/slices/repos-refresh-identity.test.ts
index 7fd32cca5ed..5ebf8b6602d 100644
--- a/src/renderer/src/store/slices/repos-refresh-identity.test.ts
+++ b/src/renderer/src/store/slices/repos-refresh-identity.test.ts
@@ -1,5 +1,7 @@
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 import type { Project, Repo } from '../../../../shared/types'
+import { getSetupScriptPromptDismissalKey } from '../../lib/setup-script-prompt'
+import { getRepoHostIdentityForParts } from './repo-host-identity'
 import { createTestStore } from './store-test-helpers'
 
 // Why: every field here is load-bearing. A scalar-only repo reconciles even when the structural
@@ -281,3 +283,21 @@ describe('repo filter identity across catalog refreshes', () => {
     expect(store.getState().filterRepoIds).toBe(first)
   })
 })
+
+describe('setup-script dismissal identity across catalog refreshes', () => {
+  it('keeps the dismissal array when a refetch prunes nothing', async () => {
+    const store = createTestStore()
+    store.setState({
+      setupScriptPromptDismissedRepoIds: [
+        getSetupScriptPromptDismissalKey(getRepoHostIdentityForParts(repo.id, 'local'))
+      ]
+    })
+    const first = store.getState().setupScriptPromptDismissedRepoIds
+
+    await store.getState().fetchRepos()
+
+    // Why: SetupScriptPromptCard Object.is-subscribes to this array. A no-op
+    // catalog refresh must not allocate just because the helper rebuilt next.
+    expect(store.getState().setupScriptPromptDismissedRepoIds).toBe(first)
+  })
+})
diff --git a/src/renderer/src/store/slices/ui.ts b/src/renderer/src/store/slices/ui.ts
index dbbc2977965..cf2f2b126b7 100644
--- a/src/renderer/src/store/slices/ui.ts
+++ b/src/renderer/src/store/slices/ui.ts
@@ -853,7 +853,7 @@ export type UISlice = {
   ) => void
   markOrcaHookRepoAlwaysTrusted: (repoId: string) => void
   clearOrcaHookTrustForRepo: (repoId: string) => void
-  setupScriptPromptDismissedRepoIds: string[]
+  setupScriptPromptDismissedRepoIds: readonly string[]
   dismissSetupScriptPrompt: (repoHostIdentity: string) => void
   setupGuideSidebarDismissed: boolean
   setSetupGuideSidebarDismissed: (dismissed: boolean) => void