diff --git a/src/renderer/src/store/project-host-setup-selector.test.ts b/src/renderer/src/store/project-host-setup-selector.test.ts
new file mode 100644
index 00000000000..610e44c1feb
--- /dev/null
+++ b/src/renderer/src/store/project-host-setup-selector.test.ts
@@ -0,0 +1,157 @@
+import { describe, expect, it } from 'vitest'
+import type { Project, ProjectHostSetup } from '../../../shared/project-types'
+import type { Repo } from '../../../shared/repo-types'
+import { getProjectHostSetupProjectionFromState } from './project-host-setup-selector'
+
+type CollectionCounters = {
+  map: number
+  flatMap: number
+  iterator: number
+  length: number
+}
+
+function countCollectionReads<T>(items: readonly T[]): {
+  value: readonly T[]
+  counters: CollectionCounters
+} {
+  const target = [...items]
+  const counters: CollectionCounters = { map: 0, flatMap: 0, iterator: 0, length: 0 }
+  const value = new Proxy(target, {
+    get(array, property) {
+      if (property === 'map' || property === 'flatMap') {
+        counters[property] += 1
+        const method = Reflect.get(array, property) as (...args: unknown[]) => unknown
+        return method.bind(array)
+      }
+      if (property === Symbol.iterator) {
+        counters.iterator += 1
+        return array[Symbol.iterator].bind(array)
+      }
+      if (property === 'length') {
+        counters.length += 1
+      }
+      return Reflect.get(array, property)
+    }
+  })
+  return { value, counters }
+}
+
+function makeRepo(id: string): Repo {
+  return {
+    id,
+    path: `/repo/${id}`,
+    displayName: id,
+    badgeColor: '#737373',
+    addedAt: 1,
+    kind: 'git'
+  }
+}
+
+function makeProject(id: string, repoId: string): Project {
+  return {
+    id,
+    displayName: id,
+    badgeColor: '#737373',
+    sourceRepoIds: [repoId],
+    createdAt: 1,
+    updatedAt: 1
+  }
+}
+
+function makeSetup(repoId: string, projectId: string): ProjectHostSetup {
+  return {
+    id: repoId,
+    projectId,
+    hostId: 'local',
+    repoId,
+    path: `/repo/${repoId}`,
+    displayName: repoId,
+    setupState: 'ready',
+    setupMethod: 'legacy-repo',
+    createdAt: 1,
+    updatedAt: 1
+  }
+}
+
+describe('project host setup selector', () => {
+  it('does not rescan stable catalog collections across 1,000 reads', () => {
+    const repos = Array.from({ length: 100 }, (_, index) => makeRepo(`repo-${index}`))
+    const projects = repos.map((repo) => makeProject(`repo:${repo.id}`, repo.id))
+    const setups = repos.map((repo) => makeSetup(repo.id, `repo:${repo.id}`))
+    const countedRepos = countCollectionReads(repos)
+    const countedProjects = countCollectionReads(projects)
+    const countedSetups = countCollectionReads(setups)
+    const state = {
+      repos: countedRepos.value,
+      projects: countedProjects.value,
+      projectHostSetups: countedSetups.value
+    }
+
+    const first = getProjectHostSetupProjectionFromState(state)
+    expect(countedRepos.counters.map).toBeGreaterThan(0)
+    expect(countedRepos.counters.iterator).toBeGreaterThan(0)
+    expect(countedProjects.counters.flatMap).toBeGreaterThan(0)
+    expect(countedSetups.counters.map).toBeGreaterThan(0)
+    countedRepos.counters.map = 0
+    countedRepos.counters.flatMap = 0
+    countedRepos.counters.iterator = 0
+    countedRepos.counters.length = 0
+    countedProjects.counters.map = 0
+    countedProjects.counters.flatMap = 0
+    countedProjects.counters.iterator = 0
+    countedProjects.counters.length = 0
+    countedSetups.counters.map = 0
+    countedSetups.counters.flatMap = 0
+    countedSetups.counters.iterator = 0
+    countedSetups.counters.length = 0
+
+    for (let read = 0; read < 1_000; read += 1) {
+      expect(getProjectHostSetupProjectionFromState(state)).toBe(first)
+    }
+
+    expect(countedRepos.counters).toEqual({ map: 0, flatMap: 0, iterator: 0, length: 0 })
+    expect(countedProjects.counters).toEqual({ map: 0, flatMap: 0, iterator: 0, length: 0 })
+    expect(countedSetups.counters).toEqual({ map: 0, flatMap: 0, iterator: 0, length: 0 })
+  })
+
+  it('invalidates the projection when hydrated setup identity changes', () => {
+    const repo = makeRepo('repo-1')
+    const repos = [repo]
+    const projects = [makeProject('repo:repo-1', repo.id)]
+    const setups = [makeSetup(repo.id, 'repo:repo-1')]
+    const first = getProjectHostSetupProjectionFromState({
+      repos,
+      projects,
+      projectHostSetups: setups
+    })
+    const replacementSetups = [...setups]
+
+    const next = getProjectHostSetupProjectionFromState({
+      repos,
+      projects,
+      projectHostSetups: replacementSetups
+    })
+
+    expect(next).not.toBe(first)
+    expect(next.projects).toBe(projects)
+    expect(next.setups).toBe(replacementSetups)
+  })
+
+  it('invalidates the projection when the repo identity changes', () => {
+    const repo = makeRepo('repo-1')
+    const repos = [repo]
+    const projects = [makeProject('repo:repo-1', repo.id)]
+    const setups = [makeSetup(repo.id, 'repo:repo-1')]
+    getProjectHostSetupProjectionFromState({ repos, projects, projectHostSetups: setups })
+
+    const replacementRepos = [makeRepo('repo-2')]
+    const next = getProjectHostSetupProjectionFromState({
+      repos: replacementRepos,
+      projects,
+      projectHostSetups: setups
+    })
+
+    expect(next.projects.map((project) => project.id)).toContain('repo:repo-2')
+    expect(next.setups.map((setup) => setup.id)).toContain('repo-2')
+  })
+})
diff --git a/src/renderer/src/store/project-host-setup-selector.ts b/src/renderer/src/store/project-host-setup-selector.ts
index 55ba345f5ba..f56b3a6e0b3 100644
--- a/src/renderer/src/store/project-host-setup-selector.ts
+++ b/src/renderer/src/store/project-host-setup-selector.ts
@@ -19,6 +19,38 @@ const normalizedProjectHostSetupProjectionCache = new WeakMap<
   AppState['repos'],
   WeakMap<Project[], WeakMap<ProjectHostSetup[], ProjectHostSetupProjection>>
 >()
+// Catalog writers replace these readonly arrays; their identities are the invalidation boundary.
+type StateProjectHostSetupProjectionCache = {
+  repos: AppState['repos']
+  projects: AppState['projects']
+  setups: AppState['projectHostSetups']
+  projection: ProjectHostSetupProjection
+}
+
+let stateProjectHostSetupProjectionCache: StateProjectHostSetupProjectionCache | null = null
+
+function getCachedStateProjectHostSetupProjection(
+  repos: AppState['repos'],
+  projects: AppState['projects'],
+  setups: AppState['projectHostSetups']
+): ProjectHostSetupProjection | undefined {
+  const cached = stateProjectHostSetupProjectionCache
+  return cached &&
+    cached.repos === repos &&
+    cached.projects === projects &&
+    cached.setups === setups
+    ? cached.projection
+    : undefined
+}
+
+function cacheStateProjectHostSetupProjection(
+  repos: AppState['repos'],
+  projects: AppState['projects'],
+  setups: AppState['projectHostSetups'],
+  projection: ProjectHostSetupProjection
+): void {
+  stateProjectHostSetupProjectionCache = { repos, projects, setups, projection }
+}
 
 function getCachedProjectHostSetupProjection(repos: AppState['repos']): ProjectHostSetupProjection {
   const cachedProjection = projectHostSetupProjectionCache.get(repos)
@@ -135,10 +167,21 @@ function getCachedNormalizedProjectHostSetupProjection(
 export function getProjectHostSetupProjectionFromState(
   state: Pick<AppState, 'repos'> & Partial<Pick<AppState, 'projects' | 'projectHostSetups'>>
 ): ProjectHostSetupProjection {
-  if (state.projects && state.projectHostSetups) {
+  const projects = state.projects
+  const projectHostSetups = state.projectHostSetups
+  if (projects && projectHostSetups) {
+    const cachedProjection = getCachedStateProjectHostSetupProjection(
+      state.repos,
+      projects,
+      projectHostSetups
+    )
+    if (cachedProjection) {
+      return cachedProjection
+    }
+
     const repoIds = new Set(state.repos.map((repo) => repo.id))
     const coveredRepoIds = new Set<string>()
-    for (const setup of state.projectHostSetups) {
+    for (const setup of projectHostSetups) {
       const repoId = typeof setup.repoId === 'string' ? setup.repoId : ''
       if (repoIds.has(repoId)) {
         coveredRepoIds.add(repoId)
@@ -147,36 +190,39 @@ export function getProjectHostSetupProjectionFromState(
         coveredRepoIds.add(setup.id)
       }
     }
+    let projection: ProjectHostSetupProjection
     if (state.repos.length > 0 && coveredRepoIds.size < repoIds.size) {
-      return mergeProjectHostSetupProjection(
+      projection = mergeProjectHostSetupProjection(
         state.repos,
-        state.projects as Project[],
-        state.projectHostSetups as ProjectHostSetup[]
+        projects as Project[],
+        projectHostSetups as ProjectHostSetup[]
+      )
+    } else {
+      const derived = getCachedProjectHostSetupProjection(state.repos)
+      const normalized = normalizeHydratedProjectHostSetupProjection(
+        state.repos,
+        projects as Project[],
+        projectHostSetups as ProjectHostSetup[],
+        derived
       )
-    }
-    const derived = getCachedProjectHostSetupProjection(state.repos)
-    const normalized = normalizeHydratedProjectHostSetupProjection(
-      state.repos,
-      state.projects as Project[],
-      state.projectHostSetups as ProjectHostSetup[],
-      derived
-    )
-    if (normalized.changed) {
       // Why: this is a zustand selector compared with Object.is, so the merged
       // result must be reference-stable per (repos, projects, setups) input or
       // every render returns a fresh object and triggers a re-render storm.
-      return getCachedNormalizedProjectHostSetupProjection(
-        state.repos,
-        state.projects as Project[],
-        state.projectHostSetups as ProjectHostSetup[],
-        derived,
-        normalized
-      )
+      projection = normalized.changed
+        ? getCachedNormalizedProjectHostSetupProjection(
+            state.repos,
+            projects as Project[],
+            projectHostSetups as ProjectHostSetup[],
+            derived,
+            normalized
+          )
+        : getCachedProvidedProjectHostSetupProjection(
+            projects as Project[],
+            projectHostSetups as ProjectHostSetup[]
+          )
     }
-    return getCachedProvidedProjectHostSetupProjection(
-      state.projects as Project[],
-      state.projectHostSetups as ProjectHostSetup[]
-    )
+    cacheStateProjectHostSetupProjection(state.repos, projects, projectHostSetups, projection)
+    return projection
   }
   return getCachedProjectHostSetupProjection(state.repos)
 }