fix: 回应 Codex 审查的 4 条意见（2×P1 + 2×P2）

- P1 state.ts reduceFor：恢复共享 uid 计数器到调用前水平（目标 session 的
  max 可能低于激活 session 已用 id，否则下次 mint 撞 id 损坏布局）；
  回归测试实证：无修复时 split 产生重复 pane id
- P1 service.ts 生命周期分类：dedupe 聚焦判定改为基于输入态的存在性
  （dedupeKey 匹配或 id 匹配都算聚焦）——按 path 去重 + 新 id 打开时
  不再对从未插入的幽灵 tab 触发 onOpen（资源泄漏源）
- P2 SideCardSection：乐观 prefs ref（optimisticRef）驱动嵌套 map 合并
  （tabsEnabled/viewersEnabled/pluginSettings），同 tick 多次写入不再
  互相丢弃；mergePluginSetting 抽纯函数 + 单测
- P2 state.ts schedulePersist：每 session 独立防抖定时器（persistTimers
  Map），定向打开不再取消其他 session 的待写；单测验证双写都落盘

tests/service.spec.ts

@@ -849,3 +849,51 @@ describe('tab meta (v0.12.0)', () => {
     expect(tabs[0]?.meta).toBeUndefined()
   })
 })
+
+describe('lifecycle classification vs dedupe (codex review fixes)', () => {
+  it('a key-dedupe focus with a NEW id fires onActivate with the REAL tab (no phantom onOpen)', () => {
+    const store = createSidebarStore()
+    const service = createBetterSidebarService(store)
+    const events: Array<{ kind: string; tabId?: string }> = []
+    service.registerTab({
+      id: 'doc',
+      title: 'Doc',
+      // Dedupe by PATH like the editor builtin — the focused tab's id
+      // differs from the newly requested id.
+      dedupeKey: (tab) => tab.path ?? '',
+      onOpen: (tab) => { events.push({ kind: 'open', tabId: tab.id }) },
+      onActivate: (tab) => { events.push({ kind: 'activate', tabId: tab.id }) },
+      component: () => null,
+    })
+    store.setSession('s1')
+    service.openTab({ type: 'doc', title: 'Doc', id: 'doc:1', path: '/a.md' })
+    expect(events).toEqual([{ kind: 'open', tabId: 'doc:1' }])
+    // Same path, NEW id: the existing tab is focused — onActivate must
+    // carry the EXISTING tab, and onOpen must NOT fire with doc:2.
+    service.openTab({ type: 'doc', title: 'Doc', id: 'doc:2', path: '/a.md' })
+    expect(events).toEqual([
+      { kind: 'open', tabId: 'doc:1' },
+      { kind: 'activate', tabId: 'doc:1' },
+    ])
+    const tabs = allLeaves(store.getSnapshot().state!.splits).flatMap(l => l.tabs).filter(t => t.type === 'doc')
+    expect(tabs.map(t => t.id)).toEqual(['doc:1'])
+  })
+
+  it('an id safety-net focus (same id) fires onActivate, not onOpen', () => {
+    const store = createSidebarStore()
+    const service = createBetterSidebarService(store)
+    const events: string[] = []
+    service.registerTab({
+      id: 'multi',
+      title: 'Multi',
+      onOpen: () => { events.push('open') },
+      onActivate: () => { events.push('activate') },
+      component: () => null,
+    })
+    store.setSession('s1')
+    service.openTab({ type: 'multi', title: 'Multi', id: 'm:1' })
+    expect(events).toEqual(['open'])
+    service.openTab({ type: 'multi', title: 'Multi', id: 'm:1' })
+    expect(events).toEqual(['open', 'activate'])
+  })
+})

tests/side-card-section.spec.tsx

@@ -20,7 +20,7 @@ import { createElement } from 'react'
 import { createSidebarStore, type SidebarStore } from '../src/client/state.ts'
 import { createBetterSidebarService, type BetterSidebarService } from '../src/client/service.ts'
 import { SIDEBAR_PREFS_DEFAULTS } from '../src/prefs-shared.ts'
-import { FeatureSettingsRows, SideCardSection, type SideCardSectionProps } from '../src/client/SideCardSection.tsx'
+import { FeatureSettingsRows, mergePluginSetting, SideCardSection, type SideCardSectionProps } from '../src/client/SideCardSection.tsx'
 
 /** One tab + one viewer + the subagent-style nested toggle under a tab. */
 function mount(): { store: SidebarStore; service: BetterSidebarService } {
@@ -216,3 +216,23 @@ describe('FeatureSettingsRows (the secondary settings popup body)', () => {
     expect(html).not.toContain('type="checkbox"')
   })
 })
+
+describe('mergePluginSetting (v0.12.0, codex review fix)', () => {
+  it('sequential merges are additive — a later write never drops an earlier key', () => {
+    // Simulates two same-tick updatePluginSetting calls: each merge spreads
+    // the map it was GIVEN, so building from the latest optimistic map
+    // preserves both keys (the pre-fix code spread the stale render-time
+    // prefs twice and the second write dropped the first key).
+    let map: Record<string, Record<string, unknown>> = {}
+    map = mergePluginSetting(map, 'my-plugin:db', 'pageSize', 25)
+    map = mergePluginSetting(map, 'my-plugin:db', 'theme', 'dark')
+    expect(map['my-plugin:db']).toEqual({ pageSize: 25, theme: 'dark' })
+    // A second descriptor's blob stays independent.
+    map = mergePluginSetting(map, 'other:view', 'refresh', true)
+    expect(map['my-plugin:db']).toEqual({ pageSize: 25, theme: 'dark' })
+    expect(map['other:view']).toEqual({ refresh: true })
+    // Overwriting one key keeps the sibling keys.
+    map = mergePluginSetting(map, 'my-plugin:db', 'pageSize', 50)
+    expect(map['my-plugin:db']).toEqual({ pageSize: 50, theme: 'dark' })
+  })
+})

tests/unit.spec.ts

@@ -1690,6 +1690,57 @@ describe('store.reduceFor (targeted opens, v0.12.0)', () => {
     expect(store.getSnapshot().state?.panelOpen).toBe(false)
     expect(store.getSnapshot().state?.splits).toBeDefined()
   })
+
+  it('reduceFor never lowers the shared uid counter below the active session needs (no pane-id collision)', () => {
+    const store = createSidebarStore()
+    // Session 'b' is cached FIRST with a LOW id range (pane:1 / tab:2).
+    store.setSession('b')
+    // Session 'a' then loads and its operations raise the shared counter
+    // well above b's max (default pane, plus fresh pane ids from splits).
+    store.setSession('a')
+    store.reduce(s => splitPane(s, 'row'))
+    const before = allLeaves(store.getSnapshot().state!.splits).map(leaf => leaf.id).sort()
+    // A targeted reduce into the OLD, low-id session must not lower the
+    // counter: the next split in the ACTIVE session would otherwise mint
+    // an id that already exists (mapLeaf visits both leaves → corruption).
+    store.reduceFor('b', (state) => state)
+    store.reduce(s => splitPane(s, 'row'))
+    const after = allLeaves(store.getSnapshot().state!.splits).map(leaf => leaf.id)
+    expect(new Set(after).size).toBe(after.length)
+    // The active session's pre-existing pane ids all survived untouched.
+    for (const id of before) expect(after).toContain(id)
+  })
+
+  it('persists each session independently (per-session debounce timers)', () => {
+    const g = globalThis as Record<string, unknown>
+    let seq = 0
+    const timers = new Map<number, () => void>()
+    const writes: string[] = []
+    g.window = {
+      clearTimeout: (id: number) => { timers.delete(id) },
+      setTimeout: (fn: () => void) => { const id = ++seq; timers.set(id, fn); return id },
+      innerWidth: 1024,
+      innerHeight: 800,
+    }
+    g.localStorage = {
+      getItem: () => null,
+      setItem: (key: string) => { writes.push(key) },
+    }
+    try {
+      const store = createSidebarStore()
+      store.setSession('a')
+      store.reduce(s => ({ ...s, expanded: ['/a'] })) // schedules persist(a)
+      store.reduceFor('b', s => ({ ...s, expanded: ['/b'] })) // schedules persist(b)
+      // A shared timer would have cancelled persist(a) — with per-session
+      // timers BOTH writes are pending and both land when they fire.
+      expect(timers.size).toBe(2)
+      for (const [, fn] of [...timers]) fn()
+      expect(writes).toEqual(['dsh-sidebar:v1:a', 'dsh-sidebar:v1:b'])
+    } finally {
+      delete g.window
+      delete g.localStorage
+    }
+  })
 })
 
 describe('tab meta persistence (v0.12.0)', () => {