diff --git a/src/main/ipc/worktrees/metadata/workspace-lineage-candidate-scan.test.ts b/src/main/ipc/worktrees/metadata/workspace-lineage-candidate-scan.test.ts
new file mode 100644
index 00000000000..e3ccee07086
--- /dev/null
+++ b/src/main/ipc/worktrees/metadata/workspace-lineage-candidate-scan.test.ts
@@ -0,0 +1,158 @@
+import { describe, expect, it, vi } from 'vitest'
+import type { Repo } from '../../../../shared/repo-types'
+import type { FolderWorkspace } from '../../../../shared/folder-workspace-types'
+import type { ProjectGroup } from '../../../../shared/project-group-types'
+import { createLineageResolutionContext } from './lineage-owner-resolution'
+import { getFolderLineageCandidateRepos } from './workspace-lineage-filtering'
+
+vi.mock('../../worktree-logic', () => ({ parseWorktreeId: vi.fn() }))
+
+function repo(id: string, fields: Partial<Repo> = {}): Repo {
+  return { id, path: `/root/${id}`, displayName: id, badgeColor: '#000', addedAt: 0, ...fields }
+}
+
+function group(id = 'group', fields: Partial<ProjectGroup> = {}): ProjectGroup {
+  return {
+    id,
+    name: id,
+    parentPath: null,
+    parentGroupId: null,
+    createdFrom: 'manual',
+    tabOrder: 0,
+    isCollapsed: false,
+    color: null,
+    createdAt: 0,
+    updatedAt: 0,
+    ...fields
+  }
+}
+
+function folder(fields: Partial<FolderWorkspace> = {}): FolderWorkspace {
+  return {
+    id: 'folder',
+    projectGroupId: 'group',
+    name: 'folder',
+    folderPath: '/root',
+    linkedTask: null,
+    comment: '',
+    isArchived: false,
+    isUnread: false,
+    isPinned: false,
+    sortOrder: 0,
+    lastActivityAt: 0,
+    createdAt: 0,
+    updatedAt: 0,
+    ...fields
+  }
+}
+
+function context(repos: Repo[], groups = [group()]) {
+  const store = {
+    getRepos: () => repos,
+    getFolderWorkspaces: () => [],
+    getProjectGroups: () => groups
+  }
+  // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: Context construction only reads these three store catalogs.
+  return createLineageResolutionContext(store as never)
+}
+
+describe('folder lineage candidate lookup', () => {
+  it('reads grouped target membership once across a large path-candidate list', () => {
+    let targetReads = 0
+    const grouped = Array.from({ length: 300 }, (_, index): Repo => ({
+      ...repo(`grouped-${index}`, { projectGroupId: 'group', path: `/elsewhere/${index}` }),
+      get connectionId() {
+        targetReads += 1
+        return null
+      }
+    }))
+    const candidates = Array.from({ length: 1_000 }, (_, index) => repo(`path-${index}`))
+    const result = getFolderLineageCandidateRepos(context([...grouped, ...candidates]), folder())
+
+    expect(result).toEqual([...grouped, ...candidates])
+    expect(targetReads).toBe(300)
+  })
+
+  it('preserves descendant-group priority, path boundaries and local/SSH membership', () => {
+    const entries = [
+      repo('path-a', { connectionId: 'a' }),
+      repo('group-b', { projectGroupId: 'nested', path: '/elsewhere', connectionId: 'b' }),
+      repo('local-null', { connectionId: null }),
+      repo('group-local', { projectGroupId: 'group' }),
+      repo('path-b', { connectionId: 'b' }),
+      repo('local-absent'),
+      repo('sibling', { path: '/root-other/repo', connectionId: 'b' }),
+      repo('root', { path: '/root', connectionId: 'b' })
+    ]
+    const snapshot = structuredClone(entries)
+    const result = getFolderLineageCandidateRepos(
+      context(entries, [group(), group('nested', { parentGroupId: 'group' })]),
+      folder()
+    )
+
+    expect(result.map((entry) => entry.id)).toEqual([
+      'group-b',
+      'group-local',
+      'local-null',
+      'path-b',
+      'local-absent',
+      'root'
+    ])
+    expect(result[0]).toBe(entries[1])
+    expect(entries).toEqual(snapshot)
+  })
+
+  it.each([
+    { folderTarget: 'a', groupTarget: 'b', expected: ['grouped', 'a'] },
+    { folderTarget: null, groupTarget: 'b', expected: ['grouped', 'b'] },
+    { folderTarget: undefined, groupTarget: undefined, expected: ['grouped', 'local'] }
+  ])(
+    'keeps explicit target precedence: $folderTarget / $groupTarget',
+    ({ folderTarget, groupTarget, expected }) => {
+      const entries = [
+        repo('a', { connectionId: 'a' }),
+        repo('b', { connectionId: 'b' }),
+        repo('local'),
+        repo('grouped', { projectGroupId: 'group', path: '/outside' })
+      ]
+      expect(
+        getFolderLineageCandidateRepos(
+          context(entries, [group('group', { connectionId: groupTarget })]),
+          folder({ connectionId: folderTarget })
+        ).map((entry) => entry.id)
+      ).toEqual(expected)
+    }
+  )
+
+  it('keeps every contained target when the folder has no grouped repositories', () => {
+    const entries = [
+      repo('local'),
+      repo('remote', { connectionId: 'a' }),
+      repo('outside', { path: '/elsewhere' })
+    ]
+    expect(getFolderLineageCandidateRepos(context(entries), folder())).toEqual(entries.slice(0, 2))
+  })
+
+  it('does not read grouped targets when there are no path candidates', () => {
+    let targetReads = 0
+    const grouped: Repo = {
+      ...repo('grouped', { projectGroupId: 'group' }),
+      get connectionId() {
+        targetReads += 1
+        return 'a'
+      }
+    }
+    expect(getFolderLineageCandidateRepos(context([grouped]), folder())).toEqual([grouped])
+    expect(targetReads).toBe(0)
+  })
+
+  it('rebuilds target membership after a later change in the same context', () => {
+    const grouped = repo('grouped', { projectGroupId: 'group', connectionId: 'a' })
+    const a = repo('a', { connectionId: 'a' })
+    const b = repo('b', { connectionId: 'b' })
+    const current = context([grouped, a, b])
+    expect(getFolderLineageCandidateRepos(current, folder())).toEqual([grouped, a])
+    grouped.connectionId = 'b'
+    expect(getFolderLineageCandidateRepos(current, folder())).toEqual([grouped, b])
+  })
+})
diff --git a/src/main/ipc/worktrees/metadata/workspace-lineage-filtering.ts b/src/main/ipc/worktrees/metadata/workspace-lineage-filtering.ts
index 3106812418c..c478b59b81a 100644
--- a/src/main/ipc/worktrees/metadata/workspace-lineage-filtering.ts
+++ b/src/main/ipc/worktrees/metadata/workspace-lineage-filtering.ts
@@ -36,18 +36,20 @@ export function getFolderLineageCandidateRepos(
   )
   const group = context.groupsById.get(folder.projectGroupId)?.[0]
   const connectionId = folder.connectionId ?? group?.connectionId ?? null
-  return connectionId
-    ? [...grouped, ...pathRepos.filter((repo) => (repo.connectionId ?? null) === connectionId)]
-    : grouped.length > 0
-      ? [
-          ...grouped,
-          ...pathRepos.filter((repo) =>
-            new Set(grouped.map((candidate) => candidate.connectionId ?? null)).has(
-              repo.connectionId ?? null
-            )
-          )
-        ]
-      : pathRepos
+  if (connectionId) {
+    return [...grouped, ...pathRepos.filter((repo) => (repo.connectionId ?? null) === connectionId)]
+  }
+  if (grouped.length === 0) {
+    return pathRepos
+  }
+  if (pathRepos.length === 0) {
+    return grouped
+  }
+  const groupedConnectionIds = new Set(grouped.map((repo) => repo.connectionId ?? null))
+  return [
+    ...grouped,
+    ...pathRepos.filter((repo) => groupedConnectionIds.has(repo.connectionId ?? null))
+  ]
 }
 
 export function resolveFolderLineageOwner(