major perf improvements

components/gmail/compose-modal.tsx

@@ -67,7 +67,8 @@ import {
   DEFAULT_IDENTITIES,
   MOCK_CONTACTS,
   SIGNATURES,
-  useCompose,
+  useComposeActions,
+  useComposeWindows,
 } from "@/lib/compose-context"
 import { useScheduledMail } from "@/lib/scheduled-mail-context"
 import type { ScheduleSendPayload } from "@/lib/api/scheduled-mail"
@@ -987,7 +988,7 @@ function SignatureButton({
   editor: Editor | null
   compose: ComposeState
 }) {
-  const { updateCompose } = useCompose()
+  const { updateCompose } = useComposeActions()
 
   const replaceSignature = useCallback(
     (sigId: string | null) => {
@@ -1233,7 +1234,7 @@ export function ComposeWindow({
     toggleMinimize,
     toggleMaximize,
     restoreComposeFromSnapshot,
-  } = useCompose()
+  } = useComposeActions()
   const { scheduleSend, requestUpdateScheduledSend, requestSendScheduledNow } =
     useScheduledMail()
   const isInline = compose.placement === "inline"
@@ -2226,7 +2227,7 @@ export function ComposeWindow({
 }
 
 export function ComposeModalManager() {
-  const { composeWindows } = useCompose()
+  const { composeWindows } = useComposeWindows()
   const isXs = useIsXs()
 
   const nonMaximized = composeWindows.filter(

components/gmail/contact-hover-card.tsx

@@ -23,7 +23,7 @@ import {
   UserPlus,
   Video,
 } from "lucide-react"
-import { useCompose } from "@/lib/compose-context"
+import { useComposeActions } from "@/lib/compose-context"
 
 export interface ContactHoverCardProps {
   /** Champ expéditeur brut (liste, conversation, etc.) */
@@ -45,7 +45,7 @@ export function ContactHoverCard({
   align = "start",
   side = "bottom",
 }: ContactHoverCardProps) {
-  const { openComposeWithInitial } = useCompose()
+  const { openComposeWithInitial } = useComposeActions()
   const [open, setOpen] = useState(false)
   const name = cleanSenderName(displayName)
   const email = resolveSenderEmail(displayName, emailOverride)

components/gmail/email-list-row.tsx

@@ -0,0 +1,49 @@
+"use client"
+
+import { useCallback } from "react"
+import type { Email } from "@/lib/email-data"
+import { useMailStore } from "@/lib/stores/mail-store"
+
+type ListMailIndex = {
+  emailById: Map<string, Email>
+  scheduledIds: Set<string>
+}
+
+/** O(n) index for list row logic — avoids repeated `allEmails.some` / `find` per row. */
+export function buildListMailIndex(emails: Email[]): ListMailIndex {
+  const emailById = new Map<string, Email>()
+  const scheduledIds = new Set<string>()
+  for (const e of emails) {
+    emailById.set(e.id, e)
+    if (e.labels?.includes("scheduled")) scheduledIds.add(e.id)
+  }
+  return { emailById, scheduledIds }
+}
+
+export type MailRowFlags = {
+  isRead: boolean
+  isStarred: boolean
+  isImportant: boolean
+}
+
+/**
+ * Per-row mail UI flags from the persisted mail store.
+ * Use inside a keyed `memo` row component (not a plain `.map` callback).
+ */
+export function useMailRowFlags(email: Email): MailRowFlags {
+  const id = email.id
+  const readOverride = useMailStore(
+    useCallback((s) => s.readOverrides[id], [id])
+  )
+  const starred = useMailStore(
+    useCallback((s) => s.starredIds.includes(id), [id])
+  )
+  const important = useMailStore(
+    useCallback((s) => s.importantIds.includes(id), [id])
+  )
+  return {
+    isRead: readOverride !== undefined ? readOverride : email.read,
+    isStarred: starred || email.starred,
+    isImportant: important || email.important,
+  }
+}

components/gmail/email-list.tsx

@@ -121,7 +121,12 @@ import {
   type MoveTarget,
 } from "@/components/gmail/move-to-menu-items"
 import { EmailView } from "./email-view"
-import { useCompose, type Contact } from "@/lib/compose-context"
+import { buildListMailIndex } from "./email-list-row"
+import {
+  useComposeActions,
+  useComposeDrafts,
+  type Contact,
+} from "@/lib/compose-context"
 import { computeFolderUnreadCounts } from "@/lib/mail-nav-metrics"
 import {
   effectiveLabels,
@@ -595,12 +600,12 @@ export function EmailList({
 }: EmailListProps) {
   const isViewMode = openMailId !== null
 
+  const { savedThreadReplyDrafts } = useComposeDrafts()
   const {
     openComposeWithInitial,
     closeAllInlineComposes,
     pruneInlineComposesToOpenThread,
-    savedThreadReplyDrafts,
+  } = useComposeActions()
-  } = useCompose()
 
   const {
     scheduledEmails,
@@ -884,13 +889,26 @@ export function EmailList({
   }, [isRefreshing, isViewMode, isXs, applyPullVisual])
 
   const filteredEmails = useMemo(() => {
-    const visible = allEmails
+    const hiddenSet = new Set(hiddenEmailIds)
-      .filter((email) => !hiddenEmailIds.includes(email.id))
+    const subtreeIdsCache = new Map<string, string[] | null>()
-      .map((e) =>
+    let visible = allEmails.filter((email) => !hiddenSet.has(email.id))
+    const hasLabelEdits =
+      labelEdits &&
+      (Object.keys(labelEdits.additions).length > 0 ||
+        Object.keys(labelEdits.removals).length > 0)
+    if (hasLabelEdits || notSpamEmailIds.length > 0) {
+      visible = visible.map((e) =>
         mergeEmailNotSpam(mergeEmailLabelEdits(e, labelEdits), notSpamEmailIds)
       )
+    }
     let rows = visible.filter((email) =>
-      emailMatchesFolder(email, selectedFolder, folderFilterCtx, navMaps)
+      emailMatchesFolder(
+        email,
+        selectedFolder,
+        folderFilterCtx,
+        navMaps,
+        subtreeIdsCache
+      )
     )
     if (selectedFolder === "inbox") {
       rows = rows.filter((email) => email.category === inboxTab)
@@ -947,6 +965,21 @@ export function EmailList({
     return pagedEmails
   }, [isXs, isViewMode, filteredEmails, mobileVisibleCount, pagedEmails])
 
+  const listMailIndex = useMemo(() => buildListMailIndex(allEmails), [allEmails])
+
+  const listRowExtras = useMemo(() => {
+    const invitationById = new Map<
+      string,
+      ReturnType<typeof resolveParsedCalendarInvitation>
+    >()
+    const attachmentsById = new Map<string, EmailAttachment[]>()
+    for (const e of listEmails) {
+      invitationById.set(e.id, resolveParsedCalendarInvitation(e))
+      attachmentsById.set(e.id, attachmentsForEmailList(e))
+    }
+    return { invitationById, attachmentsById }
+  }, [listEmails])
+
   useEffect(() => {
     if (isXs) return
     if (listPage > totalPages) {
@@ -2658,7 +2691,7 @@ export function EmailList({
 
       <div
         ref={listViewportRef}
-        className={cn(mainScrollClass, "relative overscroll-y-none", !isViewMode && "max-sm:pb-16")}
+        className={cn(mainScrollClass, "relative overscroll-y-none max-sm:pb-16")}
       >
       {!isViewMode && (
         <div
@@ -2770,8 +2803,10 @@ export function EmailList({
               const senderForSearch = email.sender.replace(/\s+/g, " ").trim()
               const isSelected = selectedEmails.includes(email.id)
               const hasInvitation = email.hasInvitation === true
-              const parsedInvitation = resolveParsedCalendarInvitation(email)
+              const parsedInvitation =
-              const attachmentList = attachmentsForEmailList(email)
+                listRowExtras.invitationById.get(email.id) ?? null
+              const attachmentList =
+                listRowExtras.attachmentsById.get(email.id) ?? []
               const isScheduled = email.labels?.includes("scheduled") === true
               const contextTargetIds = contextMenuTargetIdsForRow(
                 email.id,
@@ -2782,14 +2817,12 @@ export function EmailList({
               const allContextTargetsScheduled =
                 contextTargetIds.length > 0 &&
                 contextTargetIds.every((id) =>
-                  allEmails.some(
+                  listMailIndex.scheduledIds.has(id)
-                    (e) => e.id === id && e.labels?.includes("scheduled")
-                  )
                 )
               const scheduledCtxAnyUnread =
                 allContextTargetsScheduled &&
                 contextTargetIds.some((id) => {
-                  const em = allEmails.find((e) => e.id === id)
+                  const em = listMailIndex.emailById.get(id)
                   if (!em) return false
                   return !(readOverrides[id] ?? em.read)
                 })

components/gmail/email-view.tsx

@@ -61,7 +61,9 @@ import {
   shouldUseAttachmentPillsInPreview,
 } from "@/lib/attachment-display"
 import {
-  useCompose,
+  useComposeActions,
+  useComposeDrafts,
+  useComposeWindows,
   DEFAULT_IDENTITIES,
   type ThreadComposeKind,
   savedThreadDraftToComposePreset,
@@ -761,8 +763,9 @@ export function EmailView({
   const mainSenderName = cleanSenderName(email.sender)
   const mainSenderAddr = email.senderEmail || `${mainSenderName.toLowerCase().replace(/\s+/g, ".")}@example.com`
 
-  const { composeWindows, openComposeWithInitial, savedThreadReplyDrafts } =
+  const { composeWindows } = useComposeWindows()
-    useCompose()
+  const { savedThreadReplyDrafts } = useComposeDrafts()
+  const { openComposeWithInitial } = useComposeActions()
   const inlineCompose = useMemo(
     () =>
       composeWindows.find(

components/gmail/mobile-bottom-bar.tsx

@@ -3,7 +3,7 @@
 import { useState, useRef, useEffect, useCallback } from "react"
 import { Menu, Search, X, ChevronLeft, Pencil } from "lucide-react"
 import { Button } from "@/components/ui/button"
-import { useCompose } from "@/lib/compose-context"
+import { useComposeActions } from "@/lib/compose-context"
 
 interface MobileBottomBarProps {
   sidebarOpen: boolean
@@ -16,7 +16,7 @@ export function MobileBottomBar({
 }: MobileBottomBarProps) {
   const [searchValue, setSearchValue] = useState("")
   const inputRef = useRef<HTMLInputElement>(null)
-  const { openCompose } = useCompose()
+  const { openCompose } = useComposeActions()
 
   const hasSearch = searchValue.length > 0
 

components/gmail/move-drag-indicator.tsx

@@ -1,9 +1,13 @@
 "use client"
 
-import { useEffect, useLayoutEffect, useRef, useState } from "react"
+import { useEffect, useLayoutEffect, useRef, useState, useSyncExternalStore } from "react"
 import { createPortal } from "react-dom"
 import { Mail } from "lucide-react"
 import { EMAIL_DRAG_RETURN_MS, useEmailDrag } from "@/lib/drag-context"
+import {
+  getDragPointerSnapshot,
+  subscribeDragPointer,
+} from "@/lib/drag-pointer-store"
 import { useIsXs } from "@/hooks/use-xs"
 
 export function MoveDragIndicator() {
@@ -12,24 +16,16 @@ export function MoveDragIndicator() {
   const [mounted, setMounted] = useState(false)
   const elRef = useRef<HTMLDivElement>(null)
 
+  const livePointer = useSyncExternalStore(
+    subscribeDragPointer,
+    getDragPointerSnapshot,
+    () => ({ x: 0, y: 0 })
+  )
+
   useEffect(() => {
     setMounted(true)
   }, [])
 
-  /**
-   * When the user releases the drag outside any valid target the provider
-   * flips `phase` to "returning". We then drive a Web-Animations API tween
-   * from the current cursor position back to the origin (where the drag
-   * started) while fading out, to clearly signal "no move happened".
-   *
-   * `useLayoutEffect` (not `useEffect`) so the animation is queued in the
-   * same paint as the phase flip — otherwise the indicator visibly pauses
-   * for one frame at the release point before animating.
-   *
-   * We animate the `translate` CSS property (NOT `transform`) so the
-   * inline `transform: translate(-50%, -50%)` used for centering stays
-   * untouched and composes additively with the animated translation.
-   */
   useLayoutEffect(() => {
     if (!state) return
     if (state.phase !== "returning") return
@@ -59,14 +55,17 @@ export function MoveDragIndicator() {
   const label =
     count > 1 ? `Déplacer ${count} conversations` : "Déplacer 1 conversation"
 
+  const x = state.phase === "returning" ? state.pointerX : livePointer.x
+  const y = state.phase === "returning" ? state.pointerY : livePointer.y
+
   return createPortal(
     <div
       ref={elRef}
       aria-hidden
       className="pointer-events-none fixed z-100 select-none"
       style={{
-        left: state.pointerX,
+        left: x,
-        top: state.pointerY,
+        top: y,
         transform: "translate(-50%, -50%)",
         willChange: "translate, opacity",
       }}

components/gmail/sidebar.tsx

@@ -34,7 +34,7 @@ import { cn, formatCount } from "@/lib/utils"
 import { readXsMatches } from "@/hooks/use-xs"
 import { useState, useRef, useEffect, useMemo, type ReactNode, type CSSProperties } from "react"
 import { useEmailDropTarget } from "@/lib/drag-context"
-import { useCompose } from "@/lib/compose-context"
+import { useComposeActions } from "@/lib/compose-context"
 import {
   DropdownMenu,
   DropdownMenuContent,
@@ -504,7 +504,7 @@ export function Sidebar({
   collapsed,
   folderUnreadCounts = {},
 }: SidebarProps) {
-  const { openCompose } = useCompose()
+  const { openCompose } = useComposeActions()
   const [hoverExpanded, setHoverExpanded] = useState(false)
   const [navMoreOpen, setNavMoreOpen] = useState(false)
   const [expandedFolderIds, setExpandedFolderIds] = useState<Set<string>>(() => new Set())

lib/compose-context.tsx

@@ -393,10 +393,7 @@ function applySavedDraftsAfterClosingInline(
   return next
 }
 
-type ComposeContextValue = {
+export type ComposeActionsContextValue = {
-  composeWindows: ComposeState[]
-  /** Brouillons de réponse/transfert par id de conversation */
-  savedThreadReplyDrafts: Record<string, SavedThreadReplyDraft>
   openCompose: () => void
   openComposeWithInitial: (preset: ComposeOpenPreset) => void
   /** Réouvre une fenêtre après annulation d’un envoi en cours (nouvel id, baseline recalculée). */
@@ -413,7 +410,22 @@ type ComposeContextValue = {
   saveDraft: (id: string) => void
 }
 
-const ComposeContext = createContext<ComposeContextValue | null>(null)
+export type ComposeDraftsContextValue = {
+  /** Brouillons de réponse/transfert par id de conversation */
+  savedThreadReplyDrafts: Record<string, SavedThreadReplyDraft>
+}
+
+export type ComposeWindowsContextValue = {
+  composeWindows: ComposeState[]
+}
+
+export type ComposeContextValue = ComposeActionsContextValue &
+  ComposeDraftsContextValue &
+  ComposeWindowsContextValue
+
+const ComposeActionsContext = createContext<ComposeActionsContextValue | null>(null)
+const ComposeDraftsContext = createContext<ComposeDraftsContextValue | null>(null)
+const ComposeWindowsContext = createContext<ComposeWindowsContextValue | null>(null)
 
 export function ComposeProvider({ children }: { children: React.ReactNode }) {
   const [composeWindows, setComposeWindows] = useState<ComposeState[]>([])
@@ -660,10 +672,8 @@ export function ComposeProvider({ children }: { children: React.ReactNode }) {
     )
   }, [])
 
-  const value = useMemo<ComposeContextValue>(
+  const actionsValue = useMemo<ComposeActionsContextValue>(
     () => ({
-      composeWindows,
-      savedThreadReplyDrafts,
       openCompose,
       openComposeWithInitial,
       restoreComposeFromSnapshot,
@@ -677,8 +687,6 @@ export function ComposeProvider({ children }: { children: React.ReactNode }) {
       saveDraft,
     }),
     [
-      composeWindows,
-      savedThreadReplyDrafts,
       openCompose,
       openComposeWithInitial,
       restoreComposeFromSnapshot,
@@ -693,13 +701,50 @@ export function ComposeProvider({ children }: { children: React.ReactNode }) {
     ]
   )
 
+  const draftsValue = useMemo<ComposeDraftsContextValue>(
+    () => ({ savedThreadReplyDrafts }),
+    [savedThreadReplyDrafts]
+  )
+
+  const windowsValue = useMemo<ComposeWindowsContextValue>(
+    () => ({ composeWindows }),
+    [composeWindows]
+  )
+
   return (
-    <ComposeContext.Provider value={value}>{children}</ComposeContext.Provider>
+    <ComposeActionsContext.Provider value={actionsValue}>
+      <ComposeDraftsContext.Provider value={draftsValue}>
+        <ComposeWindowsContext.Provider value={windowsValue}>
+          {children}
+        </ComposeWindowsContext.Provider>
+      </ComposeDraftsContext.Provider>
+    </ComposeActionsContext.Provider>
   )
 }
 
-export function useCompose() {
+export function useComposeActions(): ComposeActionsContextValue {
-  const ctx = useContext(ComposeContext)
+  const ctx = useContext(ComposeActionsContext)
-  if (!ctx) throw new Error("useCompose must be used inside <ComposeProvider>")
+  if (!ctx) throw new Error("useComposeActions must be used inside <ComposeProvider>")
   return ctx
 }
+
+export function useComposeDrafts(): ComposeDraftsContextValue {
+  const ctx = useContext(ComposeDraftsContext)
+  if (!ctx) throw new Error("useComposeDrafts must be used inside <ComposeProvider>")
+  return ctx
+}
+
+export function useComposeWindows(): ComposeWindowsContextValue {
+  const ctx = useContext(ComposeWindowsContext)
+  if (!ctx) throw new Error("useComposeWindows must be used inside <ComposeProvider>")
+  return ctx
+}
+
+/** Merged read — rerenders when windows, drafts, or any action identity changes. Prefer split hooks for perf. */
+export function useCompose(): ComposeContextValue {
+  return {
+    ...useComposeActions(),
+    ...useComposeDrafts(),
+    ...useComposeWindows(),
+  }
+}

lib/drag-context.tsx

@@ -9,8 +9,12 @@ import {
   useRef,
   useState,
 } from "react"
-import { flushSync } from "react-dom"
 import { useIsXs } from "@/hooks/use-xs"
+import {
+  getDragPointerSnapshot,
+  notifyDragPointerMove,
+  resetDragPointer,
+} from "@/lib/drag-pointer-store"
 
 export type EmailDragPhase = "dragging" | "returning"
 
@@ -19,6 +23,7 @@ export type EmailDragState = {
   sourceFolderId: string
   hoveredTargetId: string | null
   hoveredTargetLabel: string | null
+  /** Last committed pointer (begin drag + snapshot when entering `returning`). */
   pointerX: number
   pointerY: number
   originX: number
@@ -57,6 +62,7 @@ export function EmailDragProvider({ children }: { children: React.ReactNode }) {
     if (!isXs) return
     stateRef.current = null
     setState(null)
+    resetDragPointer(0, 0)
   }, [isXs])
 
   const beginDrag = useCallback(
@@ -74,6 +80,7 @@ export function EmailDragProvider({ children }: { children: React.ReactNode }) {
         phase: "dragging",
       }
       stateRef.current = next
+      resetDragPointer(pointerX, pointerY)
       setState(next)
     },
     [isXs]
@@ -99,11 +106,17 @@ export function EmailDragProvider({ children }: { children: React.ReactNode }) {
     const cur = stateRef.current
     if (!cur) return
     if (cur.phase === "returning") return
-    const next: EmailDragState = { ...cur, phase: "returning", hoveredTargetId: null }
+    const p = getDragPointerSnapshot()
+    const next: EmailDragState = {
+      ...cur,
+      phase: "returning",
+      hoveredTargetId: null,
+      hoveredTargetLabel: null,
+      pointerX: p.x,
+      pointerY: p.y,
+    }
     stateRef.current = next
-    flushSync(() => {
+    setState(next)
-      setState(next)
-    })
   }, [])
 
   const completeDrop = useCallback((targetId: string, targetLabel: string) => {
@@ -111,9 +124,8 @@ export function EmailDragProvider({ children }: { children: React.ReactNode }) {
     if (!cur) return
     stateRef.current = null
     setState(null)
+    resetDragPointer(0, 0)
     if (targetId !== cur.sourceFolderId && onDropRef.current) {
-      // Defer to a microtask so we never call setState in another
-      // component synchronously from within this render/commit phase.
       const cb = onDropRef.current
       const ids = cur.ids
       queueMicrotask(() => cb(targetId, targetLabel, ids))
@@ -127,37 +139,27 @@ export function EmailDragProvider({ children }: { children: React.ReactNode }) {
     }
   }, [])
 
-  // Track cursor + handle native end-of-drag.
+  // Live pointer during native drag — updates external store only (no React state).
   useEffect(() => {
-    if (!state) return
+    if (!state || state.phase !== "dragging") return
     const onDragOver = (e: DragEvent) => {
-      setState((prev) =>
+      notifyDragPointerMove(e.clientX, e.clientY)
-        prev && prev.phase === "dragging"
-          ? { ...prev, pointerX: e.clientX, pointerY: e.clientY }
-          : prev
-      )
     }
     const onDragEnd = () => {
-      // If state still active and no drop was accepted, animate return.
-      // We deliberately keep `pointerX/Y` from the last `dragover` so the
-      // tween starts from the exact spot where the indicator was last
-      // painted. Snapping to `e.clientX/Y` would visibly shift the badge
-      // one frame before the animation begins.
-      // `flushSync` forces React to commit this state change synchronously
-      // so the indicator's `useLayoutEffect` (which starts the animation)
-      // fires in the same paint as the phase flip — no perceptible delay.
       const cur = stateRef.current
       if (!cur) return
       if (cur.phase === "returning") return
+      const p = getDragPointerSnapshot()
       const next: EmailDragState = {
         ...cur,
         phase: "returning",
         hoveredTargetId: null,
+        hoveredTargetLabel: null,
+        pointerX: p.x,
+        pointerY: p.y,
       }
       stateRef.current = next
-      flushSync(() => {
+      setState(next)
-        setState(next)
-      })
     }
     window.addEventListener("dragover", onDragOver)
     window.addEventListener("dragend", onDragEnd)
@@ -165,7 +167,7 @@ export function EmailDragProvider({ children }: { children: React.ReactNode }) {
       window.removeEventListener("dragover", onDragOver)
       window.removeEventListener("dragend", onDragEnd)
     }
-  }, [state !== null])
+  }, [state])
 
   // Auto-clear after the return animation finishes.
   useEffect(() => {
@@ -173,6 +175,7 @@ export function EmailDragProvider({ children }: { children: React.ReactNode }) {
     const id = window.setTimeout(() => {
       stateRef.current = null
       setState(null)
+      resetDragPointer(0, 0)
     }, RETURN_ANIMATION_MS + 20)
     return () => window.clearTimeout(id)
   }, [state?.phase])
@@ -211,12 +214,6 @@ export function useEmailDrag() {
 
 export const EMAIL_DRAG_RETURN_MS = RETURN_ANIMATION_MS
 
-/**
- * Helper for sidebar/folder/label rows. Returns drop-event handlers + a flag
- * indicating whether the current drag is hovering this target. If the target
- * is the drag source (same id as `sourceFolderId`), the drop is rejected so
- * the user just sees a "cancel" and no move happens.
- */
 const noopDropHandlers = {
   onDragEnter: () => {},
   onDragOver: () => {},

lib/drag-pointer-store.ts

@@ -0,0 +1,39 @@
+"use client"
+
+type Point = { x: number; y: number }
+
+const listeners = new Set<() => void>()
+let latest: Point = { x: 0, y: 0 }
+let rafId: number | null = null
+
+function emit() {
+  rafId = null
+  for (const cb of listeners) cb()
+}
+
+/** Throttle pointer notifications to at most once per animation frame. */
+export function notifyDragPointerMove(x: number, y: number) {
+  latest = { x, y }
+  if (rafId !== null) return
+  rafId = globalThis.requestAnimationFrame(emit)
+}
+
+export function getDragPointerSnapshot(): Point {
+  return latest
+}
+
+export function subscribeDragPointer(cb: () => void) {
+  listeners.add(cb)
+  return () => {
+    listeners.delete(cb)
+  }
+}
+
+export function resetDragPointer(x: number, y: number) {
+  if (rafId !== null) {
+    globalThis.cancelAnimationFrame(rafId)
+    rafId = null
+  }
+  latest = { x, y }
+  for (const cb of listeners) cb()
+}

lib/mail-folder-filter.ts

@@ -75,9 +75,21 @@ function matchesFolderLabelRow(
 function matchesLabelNav(
   email: Email,
   folderId: string,
-  maps: MailNavFolderMaps
+  maps: MailNavFolderMaps,
+  subtreeIdsCache?: Map<string, string[] | null>
 ): boolean {
-  const subtreeIds = collectSubtreeFolderIds(maps.folderTree, folderId)
+  let subtreeIds: string[] | null
+  if (subtreeIdsCache) {
+    if (!subtreeIdsCache.has(folderId)) {
+      subtreeIdsCache.set(
+        folderId,
+        collectSubtreeFolderIds(maps.folderTree, folderId)
+      )
+    }
+    subtreeIds = subtreeIdsCache.get(folderId) ?? null
+  } else {
+    subtreeIds = collectSubtreeFolderIds(maps.folderTree, folderId)
+  }
   if (subtreeIds) {
     return subtreeIds.some((id) => matchesFolderLabelRow(email, id, maps))
   }
@@ -88,7 +100,9 @@ export function emailMatchesFolder(
   email: Email,
   folderId: string,
   ctx: MailFolderFilterCtx,
-  maps?: MailNavFolderMaps | null
+  maps?: MailNavFolderMaps | null,
+  /** Réutiliser entre appels (ex. `computeFolderUnreadCounts`) pour éviter de rescanner l’arbre à chaque mail. */
+  subtreeIdsCache?: Map<string, string[] | null>
 ): boolean {
   const nav = resolveNavMaps(maps)
 
@@ -127,7 +141,7 @@ export function emailMatchesFolder(
   }
 
   if (nav.folderIdToLabel[folderId]) {
-    return matchesLabelNav(email, folderId, nav)
+    return matchesLabelNav(email, folderId, nav, subtreeIdsCache)
   }
 
   if (email.labels?.includes(folderId)) return true

lib/mail-nav-metrics.ts

@@ -76,13 +76,14 @@ export function countUnreadInFolder(
   ctx: MailFolderFilterCtx,
   hiddenIds: Set<string>,
   readOverrides: Record<string, boolean>,
-  maps?: MailNavFolderMaps | null
+  maps?: MailNavFolderMaps | null,
+  subtreeIdsCache?: Map<string, string[] | null>
 ): number {
   if (folderId === "scheduled" || folderId === "snoozed") {
     let n = 0
     for (const e of allEmails) {
       if (hiddenIds.has(e.id)) continue
-      if (!emailMatchesFolder(e, folderId, ctx, maps)) continue
+      if (!emailMatchesFolder(e, folderId, ctx, maps, subtreeIdsCache)) continue
       n++
     }
     return n
@@ -91,7 +92,7 @@ export function countUnreadInFolder(
   let n = 0
   for (const e of allEmails) {
     if (hiddenIds.has(e.id)) continue
-    if (!emailMatchesFolder(e, folderId, ctx, maps)) continue
+    if (!emailMatchesFolder(e, folderId, ctx, maps, subtreeIdsCache)) continue
     if (!effectiveRead(e, readOverrides)) n++
   }
   return n
@@ -106,17 +107,28 @@ export function computeFolderUnreadCounts(
   labelEdits?: LabelEditState,
   notSpamEmailIds?: readonly string[]
 ): Record<string, number> {
-  let pool =
+  let pool: Email[] =
     labelEdits &&
     (Object.keys(labelEdits.additions).length > 0 ||
       Object.keys(labelEdits.removals).length > 0)
       ? applyLabelEditsToEmails(allEmails, labelEdits)
       : allEmails
-  pool = pool.map((e) => mergeEmailNotSpam(e, notSpamEmailIds ?? []))
+  if (notSpamEmailIds && notSpamEmailIds.length > 0) {
+    pool = pool.map((e) => mergeEmailNotSpam(e, notSpamEmailIds))
+  }
   const hidden = new Set(hiddenEmailIds)
+  const subtreeIdsCache = new Map<string, string[] | null>()
   const out: Record<string, number> = {}
   for (const id of allSidebarNavFolderIds(maps)) {
-    out[id] = countUnreadInFolder(pool, id, ctx, hidden, readOverrides, maps)
+    out[id] = countUnreadInFolder(
+      pool,
+      id,
+      ctx,
+      hidden,
+      readOverrides,
+      maps,
+      subtreeIdsCache
+    )
   }
   return out
 }

lib/stores/debounced-json-storage.ts

@@ -0,0 +1,100 @@
+"use client"
+
+import {
+  createJSONStorage,
+  type PersistStorage,
+  type StateStorage,
+  type StorageValue,
+} from "zustand/middleware"
+
+const DEFAULT_DEBOUNCE_MS = 220
+
+/** In-memory fallback when `localStorage` is missing (SSR) or throws (private mode, etc.). */
+function createMemoryStateStorage(): StateStorage {
+  const data = new Map<string, string>()
+  return {
+    getItem: (name) => data.get(name) ?? null,
+    setItem: (name, value) => {
+      data.set(name, value)
+    },
+    removeItem: (name) => {
+      data.delete(name)
+    },
+  }
+}
+
+function getPersistBackingStorage(): StateStorage {
+  if (typeof window === "undefined") {
+    return createMemoryStateStorage()
+  }
+  try {
+    return window.localStorage
+  } catch {
+    return createMemoryStateStorage()
+  }
+}
+
+/**
+ * JSON persist storage that debounces writes to `localStorage` so rapid
+ * store updates do not block the main thread on every mutation.
+ * Flushes pending keys on a timer, `beforeunload`, and `pagehide`.
+ * Uses in-memory storage during SSR or when `localStorage` is unavailable.
+ */
+function buildDebouncedJsonStorage(): PersistStorage<unknown> {
+  const base =
+    createJSONStorage(getPersistBackingStorage) ??
+    createJSONStorage(() => createMemoryStateStorage())
+  if (!base) {
+    throw new Error("[debounced-json-storage] failed to create JSON storage")
+  }
+
+  const pending = new Map<string, StorageValue<unknown>>()
+  const timers = new Map<string, ReturnType<typeof globalThis.setTimeout>>()
+
+  const flushKey = (name: string) => {
+    const t = timers.get(name)
+    if (t !== undefined) {
+      globalThis.clearTimeout(t)
+      timers.delete(name)
+    }
+    const value = pending.get(name)
+    if (value === undefined) return
+    pending.delete(name)
+    base.setItem(name, value)
+  }
+
+  const flushAll = () => {
+    for (const name of [...pending.keys()]) flushKey(name)
+  }
+
+  if (typeof window !== "undefined") {
+    window.addEventListener("beforeunload", flushAll)
+    window.addEventListener("pagehide", flushAll)
+  }
+
+  return {
+    getItem: (name) => base.getItem(name),
+    setItem: (name, value) => {
+      pending.set(name, value)
+      const existing = timers.get(name)
+      if (existing !== undefined) globalThis.clearTimeout(existing)
+      const id = globalThis.setTimeout(() => {
+        timers.delete(name)
+        flushKey(name)
+      }, DEFAULT_DEBOUNCE_MS)
+      timers.set(name, id)
+    },
+    removeItem: (name) => {
+      const existing = timers.get(name)
+      if (existing !== undefined) {
+        globalThis.clearTimeout(existing)
+        timers.delete(name)
+      }
+      pending.delete(name)
+      return base.removeItem(name)
+    },
+  }
+}
+
+/** Shared instance for all zustand `persist` stores in this app. */
+export const debouncedPersistJSONStorage = buildDebouncedJsonStorage()

lib/stores/mail-store.ts

@@ -2,6 +2,7 @@
 
 import { create } from "zustand"
 import { persist } from "zustand/middleware"
+import { debouncedPersistJSONStorage } from "@/lib/stores/debounced-json-storage"
 
 /**
  * Persistent mail store — survives across navigations and page reloads.
@@ -186,6 +187,7 @@ export const useMailStore = create<MailStoreState & MailStoreActions>()(
     }),
     {
       name: "ultimail-mail-state",
+      storage: debouncedPersistJSONStorage,
       version: 3,
       migrate: (persisted, version) => {
         const state = persisted as MailStoreState & { notSpamEmailIds?: string[] }

lib/stores/nav-store.ts

@@ -2,6 +2,7 @@
 
 import { create } from "zustand"
 import { persist } from "zustand/middleware"
+import { debouncedPersistJSONStorage } from "@/lib/stores/debounced-json-storage"
 import {
   cloneDefaultFolderTree,
   cloneDefaultLabelRows,
@@ -386,6 +387,7 @@ export const useNavStore = create<NavStoreState & NavStoreActions>()(
     }),
     {
       name: "ultimail-nav-state",
+      storage: debouncedPersistJSONStorage,
       version: 1,
     }
   )

lib/stores/scheduled-store.ts

@@ -2,6 +2,7 @@
 
 import { create } from "zustand"
 import { persist } from "zustand/middleware"
+import { debouncedPersistJSONStorage } from "@/lib/stores/debounced-json-storage"
 import type { Email } from "@/lib/email-data"
 
 export type ScheduleSendPayload = {
@@ -242,6 +243,7 @@ export const useScheduledStore = create<ScheduledStoreState & ScheduledStoreActi
     }),
     {
       name: "ultimail-scheduled-state",
+      storage: debouncedPersistJSONStorage,
       version: 1,
     }
   )