diff --git a/src/background/index.ts b/src/background/index.ts
index de847c4..3a6e6fa 100644
--- a/src/background/index.ts
+++ b/src/background/index.ts
@@ -228,8 +228,19 @@ async function handleMessage(msg: Message): Promise<unknown> {
       await dropTab(msg.tabId)
       return
     }
-    case 'activateTab':
-      return chrome.tabs.update(msg.tabId, { active: true })
+    case 'activateTab': {
+      try {
+        await chrome.tabs.update(msg.tabId, { active: true })
+        return
+      } catch (e) {
+        // Stale ref: the tab is gone but folder.items still points at
+        // its id. Drop the ref so the next refresh removes the ghost
+        // row, then surface a generic "missing tab" error to the panel.
+        console.warn('[Spaces] activateTab failed; dropping ref', msg.tabId, e)
+        await dropTab(msg.tabId)
+        throw new Error('Tab is no longer available')
+      }
+    }
     case 'reconcile':
       return reconcileIfStale()
     case 'pinUrl':
diff --git a/src/background/reconcile.test.ts b/src/background/reconcile.test.ts
index 40f6faa..af90f3a 100644
--- a/src/background/reconcile.test.ts
+++ b/src/background/reconcile.test.ts
@@ -63,6 +63,31 @@ describe('reconcile', () => {
     expect(store.folders[space.rootFolderId].items.filter(it => it.kind === 'tab' && it.tabId === t1.id!)).toEqual([])
   })
 
+  it('dedupes duplicate tab refs within a folder even when no tabs are dead', async () => {
+    const space = await createSpace({ name: 'S', color: 'blue', windowId: 1 })
+    const t1 = await chrome.tabs.create({ windowId: 1 })
+    await registerTab(t1)
+
+    // Simulate the race that this fix targets: the same live tabId
+    // appears twice in root.items. (In the field this comes from
+    // switchTo's starter push running concurrently with
+    // chrome.tabs.onCreated → registerTab.)
+    const dirty = await loadStore()
+    dirty.folders[space.rootFolderId].items.push({ kind: 'tab', tabId: t1.id! })
+    dirty.folders[space.rootFolderId].items.push({ kind: 'tab', tabId: t1.id! })
+    await chrome.storage.local.set({ spaceStore: dirty })
+
+    const result = await reconcile()
+    // No dead tabs to report, but we still wrote the dedup-ed store.
+    expect(result.dropped).toBe(0)
+
+    const store = await loadStore()
+    const tabRefs = store.folders[space.rootFolderId].items.filter(
+      (it) => it.kind === 'tab' && it.tabId === t1.id!,
+    )
+    expect(tabRefs).toHaveLength(1)
+  })
+
   describe('reconcileIfStale', () => {
     it('throttles reconcile calls within 30 seconds', async () => {
       vi.useFakeTimers()
diff --git a/src/background/reconcile.ts b/src/background/reconcile.ts
index cc91c45..c0f4613 100644
--- a/src/background/reconcile.ts
+++ b/src/background/reconcile.ts
@@ -4,6 +4,8 @@ import { pruneDeadTabs } from './space-manager'
 // Drop tab refs and TabRecord entries for tabs that no longer exist.
 // Called at SW startup; the store can drift if tabs were closed while the
 // SW was suspended (MV3 events fired during suspension are not replayed).
+// Also kicks in when a folder's items hold duplicate entries for the
+// same tabId — pruneDeadTabs dedupes those alongside the dead-tab cull.
 export async function reconcile(): Promise<{ dropped: number }> {
   const tabs = await chrome.tabs.query({})
   const liveIds = new Set(
@@ -11,15 +13,20 @@ export async function reconcile(): Promise<{ dropped: number }> {
   )
   const before = await loadStore()
   const droppedIds = new Set<number>()
+  let hasDuplicate = false
   for (const id of Object.keys(before.tabs).map(Number)) {
     if (!liveIds.has(id)) droppedIds.add(id)
   }
   for (const f of Object.values(before.folders)) {
+    const seen = new Set<number>()
     for (const it of f.items) {
-      if (it.kind === 'tab' && !liveIds.has(it.tabId)) droppedIds.add(it.tabId)
+      if (it.kind !== 'tab') continue
+      if (!liveIds.has(it.tabId)) droppedIds.add(it.tabId)
+      else if (seen.has(it.tabId)) hasDuplicate = true
+      else seen.add(it.tabId)
     }
   }
-  if (droppedIds.size === 0) return { dropped: 0 }
+  if (droppedIds.size === 0 && !hasDuplicate) return { dropped: 0 }
   await updateStore((s) => {
     pruneDeadTabs(s, liveIds)
   })
diff --git a/src/background/space-manager.ts b/src/background/space-manager.ts
index 0e6bb94..23689d8 100644
--- a/src/background/space-manager.ts
+++ b/src/background/space-manager.ts
@@ -598,12 +598,24 @@ export async function switchTo(spaceId: SpaceId, windowId?: number): Promise<voi
       if (typeof created.id === 'number') {
         activatedId = created.id
         targetTabIds.add(created.id)
+        // chrome.tabs.onCreated → registerTab runs concurrently and (now
+        // that activeSpaceByWindow points at this Space) appends the new
+        // tab into root.items too. Without this guard the two writers
+        // each push, producing a duplicate item entry every time switchTo
+        // runs through the starter path.
         await updateStore((s) => {
           s.tabs[created.id!] = { tabId: created.id!, windowId: winId }
           const sp = s.spaces[spaceId]
           if (!sp) return
           const root = s.folders[sp.rootFolderId]
-          if (root) root.items.push({ kind: 'tab', tabId: created.id! })
+          if (!root) return
+          if (
+            !root.items.some(
+              (it) => it.kind === 'tab' && it.tabId === created.id!,
+            )
+          ) {
+            root.items.push({ kind: 'tab', tabId: created.id! })
+          }
         })
       }
     } catch {
@@ -1091,15 +1103,25 @@ export async function reattachOrphanSpaces(): Promise<void> {
   })
 }
 
-// Used by reconcile to drop stale tab refs.
+// Used by reconcile to drop stale tab refs. Also deduplicates tab refs
+// within each folder — race-condition fallouts (e.g. a previous
+// registerTab vs switchTo starter push) can leave the same tabId in
+// folder.items more than once, which surfaces as ghost rows in the side
+// panel that keep replicating across switches. Keeping the dedup pass
+// here means every reconcile sweep (panel mount + visibility change)
+// self-heals existing damage even if the original racer is long gone.
 export function pruneDeadTabs(s: SpaceStore, liveTabIds: Set<number>): boolean {
   let changed = false
   for (const f of Object.values(s.folders)) {
     const before = f.items.length
+    const seenTabs = new Set<number>()
     f.items = f.items.filter((it) => {
       if (it.kind === 'folder') return true
       if (it.kind === 'live') return true
-      return liveTabIds.has(it.tabId)
+      if (!liveTabIds.has(it.tabId)) return false
+      if (seenTabs.has(it.tabId)) return false
+      seenTabs.add(it.tabId)
+      return true
     })
     if (f.items.length !== before) changed = true
     if (f.live) {