diff --git a/src/shared/workspace-doc-history.test.ts b/src/shared/workspace-doc-history.test.ts
index 15ea1c2d3d7..8d69b22d712 100644
--- a/src/shared/workspace-doc-history.test.ts
+++ b/src/shared/workspace-doc-history.test.ts
@@ -53,4 +53,36 @@ describe('normalizeWorkspaceDocHistoryEntries', () => {
     expect(normalizeWorkspaceDocHistoryTitle('', DOC)).toBe('a.html')
     expect(normalizeWorkspaceDocHistoryTitle('Report', DOC)).toBe('Report')
   })
+  it('indexes document identity while deduplicating a large legacy history', () => {
+    let reads = 0
+    const entries = Array.from({ length: 10_000 }, (_, i) =>
+      entry({
+        docLocation: {
+          kind: 'workspace-doc',
+          get worktreeId() {
+            reads++
+            return 'wt-1'
+          },
+          filePath: `/repo/${i % 99}.html`
+        },
+        lastVisitedAt: i
+      })
+    )
+    const result = normalizeWorkspaceDocHistoryEntries(entries)
+    expect(reads).toBeLessThanOrEqual(20_000)
+    expect(result).toHaveLength(99)
+    expect(result.map((row) => row.lastVisitedAt)).toEqual(
+      Array.from({ length: 99 }, (_, i) => 9999 - i)
+    )
+  })
+
+  it('keeps workspace and file identity separate, including separator-like text', () => {
+    const locations = [
+      { kind: 'workspace-doc' as const, worktreeId: 'a::b', filePath: 'c' },
+      { kind: 'workspace-doc' as const, worktreeId: 'a', filePath: 'b::c' },
+      { kind: 'workspace-doc' as const, worktreeId: 'a', filePath: 'B::c' }
+    ]
+    const entries = locations.map((docLocation) => entry({ docLocation }))
+    expect(normalizeWorkspaceDocHistoryEntries(entries)).toEqual(entries)
+  })
 })
diff --git a/src/shared/workspace-doc-history.ts b/src/shared/workspace-doc-history.ts
index bf9e111dc8f..24e3a5c2311 100644
--- a/src/shared/workspace-doc-history.ts
+++ b/src/shared/workspace-doc-history.ts
@@ -1,4 +1,3 @@
-import { browserPageDocLocationsEqual } from './browser-page-doc-location'
 import type { BrowserPageDocLocation } from './browser-workspace-types'
 import { isDocPreviewUrl } from './doc-preview-scheme'
 
@@ -47,6 +46,7 @@ export function normalizeWorkspaceDocHistoryEntries(
   entries: readonly WorkspaceDocHistoryEntry[]
 ): WorkspaceDocHistoryEntry[] {
   const normalized: WorkspaceDocHistoryEntry[] = []
+  const seenPathsByWorktree = new Map<string, Set<string>>()
   const candidates = [...entries].sort((a, b) => b.lastVisitedAt - a.lastVisitedAt)
   for (const entry of candidates) {
     if (
@@ -56,11 +56,19 @@ export function normalizeWorkspaceDocHistoryEntries(
     ) {
       continue
     }
-    if (
-      normalized.some((kept) => browserPageDocLocationsEqual(kept.docLocation, entry.docLocation))
-    ) {
+    // Nested, not a joined key: any separator would collide with worktree ids or paths that
+    // contain it. Must stay equivalent to `browserPageDocLocationsEqual`, which the store's
+    // doc-history dedupe still uses — divergence would show up as duplicate dropdown rows.
+    const { worktreeId, filePath } = entry.docLocation
+    const seenPaths = seenPathsByWorktree.get(worktreeId)
+    if (seenPaths?.has(filePath)) {
       continue
     }
+    if (seenPaths) {
+      seenPaths.add(filePath)
+    } else {
+      seenPathsByWorktree.set(worktreeId, new Set([filePath]))
+    }
     normalized.push({
       ...entry,
       title: normalizeWorkspaceDocHistoryTitle(entry.title, entry.docLocation)