feat: DSH-native flat chrome + Side card settings (plugin-owned settings wire)

- Remove every box-shadow; panel uses the native sidebar fill surface
  (--dsw-specific-sidebar-fill) with a hairline border, the collapse
  control becomes the native 36px circular rail button, the active tab
  uses the native interactive-bg-active fill, and rows/typography follow
  the native 34px/14px session-row recipe.
- New 'Side card' settings section in the DSH Settings shell: open-by-
  default for new conversations (boolean) and default width share as a
  percent of the window (20-60). New sessions seed from these prefs;
  existing per-session layouts stay untouched.
- The settings namespace is read/written through the plugin's own fenced
  /sidebar routes calling the settings seam in-process: the DSH settings
  RPC domain only serves allowlisted namespaces to configuration clients,
  so third-party namespaces cannot use connection.api.settings (reads are
  silently filtered, writes refused with 'not exposed'). The seam still
  persists to the user settings document with revision-guarded writes.

README.md

@@ -101,9 +101,15 @@
 
 ### 🎨 界面风格
 
-- 行/按钮/间距/动效对齐应用自身组件：34px 圆角树行、28px 圆形图标按钮、挂载淡入
+- 完全对齐 DSH 原生 chrome：**无阴影**的扁平面板（`--dsw-specific-sidebar-fill` 表面 + hairline 边框）、原生 rail 圆形图标按钮、`interactive-bg-active` 选中填充、34px/14px 原生行规格
 - 键盘焦点可见（focus-visible 环）、`prefers-reduced-motion` 下关闭全部动画
 
+### ⚙️ Side card 设置（DSH 设置页）
+
+- 设置页新增 **Side card（侧边卡片）** 分区，持久化到 DSH 用户设置文档：
+  - **新会话默认打开**：新建会话是否自动展开侧边卡片（已存在的会话保持各自布局）
+  - **默认宽度占比**：新建会话时侧边卡片占窗口宽度的百分比（20–60，默认 30）
+
 ## ⌨️ 快捷键速查
 
 | 操作 | 按键 |

package.json

@@ -54,11 +54,13 @@
     "@deepseek-ai/dsh-client-schema-form": "^0.0.1",
     "@deepseek-ai/dsh-client-ui-conversation": "^0.0.1",
     "@deepseek-ai/dsh-client-ui-primitives": "^0.0.1",
+    "@deepseek-ai/dsh-client-ui-settings": "^0.0.1",
     "@deepseek-ai/dsh-client-ui-slots": "^0.0.1",
     "@deepseek-ai/dsh-client-web-react": "^0.0.1",
     "@deepseek-ai/dsh-host-webserver": "^0.0.1",
     "@deepseek-ai/dsh-invariants": "^0.0.1",
     "@deepseek-ai/dsh-session": "^0.0.1",
+    "@deepseek-ai/dsh-settings": "^0.0.1",
     "cordis": "^4.0.0-rc.7",
     "react": "^18.2.0",
     "react-dom": "^18.2.0"
@@ -97,11 +99,13 @@
     "@deepseek-ai/dsh-client-schema-form": "link:/Users/menghuan/.dsh/source/current/packages/client/schema-form",
     "@deepseek-ai/dsh-client-ui-conversation": "link:/Users/menghuan/.dsh/source/current/packages/client/ui-conversation",
     "@deepseek-ai/dsh-client-ui-primitives": "link:/Users/menghuan/.dsh/source/current/packages/client/ui-primitives",
+    "@deepseek-ai/dsh-client-ui-settings": "link:/Users/menghuan/.dsh/source/current/packages/client/ui-settings",
     "@deepseek-ai/dsh-client-ui-slots": "link:/Users/menghuan/.dsh/source/current/packages/client/ui-slots",
     "@deepseek-ai/dsh-client-web-react": "link:/Users/menghuan/.dsh/source/current/packages/client/web-react",
     "@deepseek-ai/dsh-host-webserver": "link:/Users/menghuan/.dsh/source/current/packages/host/webserver",
     "@deepseek-ai/dsh-invariants": "link:/Users/menghuan/.dsh/source/current/packages/support/invariants",
     "@deepseek-ai/dsh-session": "link:/Users/menghuan/.dsh/source/current/packages/core/session",
+    "@deepseek-ai/dsh-settings": "link:/Users/menghuan/.dsh/source/current/packages/settings/settings",
     "@types/node": "^24.0.0",
     "@types/react": "~18.3.1",
     "@types/react-dom": "~18.3.1",

pnpm-lock.yaml

@@ -105,6 +105,9 @@ importers:
       '@deepseek-ai/dsh-client-ui-primitives':
         specifier: link:/Users/menghuan/.dsh/source/current/packages/client/ui-primitives
         version: link:../../.dsh/source/current/packages/client/ui-primitives
+      '@deepseek-ai/dsh-client-ui-settings':
+        specifier: link:/Users/menghuan/.dsh/source/current/packages/client/ui-settings
+        version: link:../../.dsh/source/current/packages/client/ui-settings
       '@deepseek-ai/dsh-client-ui-slots':
         specifier: link:/Users/menghuan/.dsh/source/current/packages/client/ui-slots
         version: link:../../.dsh/source/current/packages/client/ui-slots
@@ -120,6 +123,9 @@ importers:
       '@deepseek-ai/dsh-session':
         specifier: link:/Users/menghuan/.dsh/source/current/packages/core/session
         version: link:../../.dsh/source/current/packages/core/session
+      '@deepseek-ai/dsh-settings':
+        specifier: link:/Users/menghuan/.dsh/source/current/packages/settings/settings
+        version: link:../../.dsh/source/current/packages/settings/settings
       '@types/node':
         specifier: ^24.0.0
         version: 24.13.3

src/client/SideCardSection.module.css

@@ -0,0 +1,90 @@
+/**
+ * Side card settings section chrome: the native settings-row recipe (figma
+ * row 16/0 padding, hairline separator, 14px/22px title, 12px/17px desc) with
+ * the native checkbox (16px, brand accent) and the Input atom + "%" suffix.
+ * The shell strips the last row's separator via the trailing-child rule.
+ */
+
+.section {
+  display: flex;
+  flex-direction: column;
+  width: 100%;
+}
+
+.section > :last-child {
+  border-bottom: none;
+}
+
+.row {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 16px;
+  padding: 16px 0;
+  border-bottom: 1px solid var(--dsw-alias-border-l2);
+  cursor: pointer;
+}
+
+.rowText {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+  min-width: 0;
+}
+
+.title {
+  font-size: 14px;
+  line-height: 22px;
+  color: var(--dsw-alias-label-primary);
+}
+
+.desc {
+  font-size: 12px;
+  line-height: 17px;
+  color: var(--dsw-alias-label-secondary);
+}
+
+/* Native checkbox: 16px, brand accent, no custom chrome (RiskConfirmation recipe). */
+.toggle {
+  flex: none;
+  width: 16px;
+  height: 16px;
+  margin: 0;
+  accent-color: var(--dsw-alias-button-primary-fill);
+  cursor: pointer;
+}
+
+.toggle:focus-visible {
+  outline: 2px solid var(--dsw-alias-border-l4);
+  outline-offset: 2px;
+}
+
+.control {
+  flex: none;
+  display: flex;
+  align-items: center;
+  gap: 6px;
+}
+
+.percentInput {
+  width: 76px;
+}
+
+.suffix {
+  font-size: 14px;
+  line-height: 22px;
+  color: var(--dsw-alias-label-secondary);
+}
+
+.error {
+  padding: 10px 0 2px;
+  font-size: 12px;
+  line-height: 17px;
+  color: var(--dsw-alias-state-error-primary);
+}
+
+@media (prefers-reduced-motion: reduce) {
+  .row {
+    transition: none;
+  }
+}

src/client/SideCardSection.tsx

@@ -0,0 +1,181 @@
+/**
+ * "Side card" settings section: the user-facing preferences for the sidebar
+ * panel, rendered natively in the DSH Settings shell (nav label "Side card").
+ * Two rows:
+ *  - new conversations open the panel by default (native checkbox), and
+ *  - the default panel width as a percent of the window (number input + %).
+ *
+ * Writes ride the plugin's own fenced settings route (the host calls the
+ * settings seam in-process — the DSH settings RPC domain does not serve
+ * third-party namespaces to configuration clients); the shared SidebarStore
+ * is refreshed on success so the very next brand-new session seeds from the
+ * new values. Any failure reverts the optimistic UI and shows the wire error
+ * inline — a broken settings surface never crashes the shell.
+ */
+import { useEffect, useRef, useState } from 'react'
+import { Input } from '@deepseek-ai/dsh-client-ui-primitives'
+// Type-only: pulls the settings shell's SlotMap merges ('settings.section').
+import type {} from '@deepseek-ai/dsh-client-ui-settings/client'
+import type { PropsRuntime } from '@deepseek-ai/dsh-client-ui-slots'
+import {
+  clampWidthPercent,
+  WIDTH_PERCENT_MAX,
+  WIDTH_PERCENT_MIN,
+  type SidebarPrefs,
+} from '../prefs-shared.ts'
+import { api } from './api.ts'
+import { parsePrefs } from './prefs.ts'
+import { t } from './locales.ts'
+import type { SidebarStore } from './state.ts'
+import css from './SideCardSection.module.css'
+
+/** Injected business face: the shared store (prefs cache). */
+export interface SideCardSectionInjected {
+  store: SidebarStore
+}
+
+/** Full section props: the runtime share plus the injected face. */
+export type SideCardSectionProps = PropsRuntime<'settings.section'> & SideCardSectionInjected
+
+/** Map one wire failure to the inline message (the conflict gets friendly copy). */
+function messageOf(error: unknown): string {
+  if (error instanceof Error && 'code' in error && (error as { code?: unknown }).code === 'settings-conflict') {
+    return `${t('settingsSaveFailed')} ${t('settingsConflict')}`
+  }
+  return `${t('settingsSaveFailed')} ${error instanceof Error ? error.message : String(error)}`
+}
+
+/**
+ * Render the Side card preferences section.
+ * @param props - composed slot props (runtime share + injected store).
+ * @returns the section element tree.
+ */
+export function SideCardSection({ store }: SideCardSectionProps) {
+  const [prefs, setPrefs] = useState<SidebarPrefs>(() => store.getPrefs())
+  const [widthDraft, setWidthDraft] = useState<string>(String(store.getPrefs().defaultWidthPercent))
+  const [error, setError] = useState<string | null>(null)
+
+  // The settings document revision (guards concurrent writes). A ref: commits
+  // read the freshest value at execution time, no re-render needed.
+  const revisionRef = useRef<number | undefined>(undefined)
+  // Whether the user already wrote since mount: the mount read must not
+  // clobber a newer optimistic edit (the window is milliseconds, but a slow
+  // route must never silently revert a just-made change).
+  const dirtyRef = useRef(false)
+  // Serialize commits: a queued write must observe the previous write's
+  // revision; a failed write must not poison the queue for later ones.
+  const inFlightRef = useRef<Promise<unknown>>(Promise.resolve())
+
+  // Sync the persisted document once on mount: the revision and the current
+  // values (another tab may have changed them since the store hydrated).
+  useEffect(() => {
+    let cancelled = false
+    void api.settingsGet().then((view) => {
+      if (cancelled) return
+      revisionRef.current = view.revision
+      if (dirtyRef.current) return
+      const next = parsePrefs(view.value)
+      setPrefs(next)
+      setWidthDraft(String(next.defaultWidthPercent))
+    }).catch(() => { /* the store's defaults stay authoritative */ })
+    return () => { cancelled = true }
+  }, [])
+
+  /** Persist one patch through the settings route (serialized, revision-guarded). */
+  const commit = (patch: Partial<SidebarPrefs>): Promise<{ ok: boolean; prefs: SidebarPrefs }> => {
+    dirtyRef.current = true
+    const run = inFlightRef.current.then(async () => {
+      const view = await api.settingsUpdate(
+        { ...patch },
+        revisionRef.current,
+      )
+      const next = parsePrefs(view.value)
+      revisionRef.current = view.revision
+      store.setPrefs(next)
+      return next
+    })
+    // A failed commit must not poison the queue: later writes still run.
+    inFlightRef.current = run.then(() => undefined, () => undefined)
+    return run.then(
+      (next) => ({ ok: true, prefs: next }),
+      (caught) => {
+        setError(messageOf(caught))
+        return { ok: false, prefs }
+      },
+    )
+  }
+
+  /** Settle one commit: success adopts the server values, failure reverts. */
+  const applyOutcome = (previous: SidebarPrefs, outcome: { ok: boolean; prefs: SidebarPrefs }): void => {
+    const settled = outcome.ok ? outcome.prefs : previous
+    setPrefs(settled)
+    setWidthDraft(String(settled.defaultWidthPercent))
+  }
+
+  const onToggle = (next: boolean): void => {
+    const previous = prefs
+    setPrefs({ ...previous, openByDefault: next })
+    setError(null)
+    void commit({ openByDefault: next }).then(outcome => applyOutcome(previous, outcome))
+  }
+
+  const commitWidth = (): void => {
+    const parsed = Number(widthDraft)
+    if (!Number.isFinite(parsed)) {
+      setWidthDraft(String(prefs.defaultWidthPercent))
+      return
+    }
+    const clamped = clampWidthPercent(parsed)
+    const previous = prefs
+    setPrefs({ ...previous, defaultWidthPercent: clamped })
+    setWidthDraft(String(clamped))
+    setError(null)
+    void commit({ defaultWidthPercent: clamped }).then(outcome => applyOutcome(previous, outcome))
+  }
+
+  return (
+    <div className={css.section}>
+      <label className={css.row}>
+        <span className={css.rowText}>
+          <span className={css.title}>{t('settingsOpenTitle')}</span>
+          <span className={css.desc}>{t('settingsOpenDesc')}</span>
+        </span>
+        <input
+          type="checkbox"
+          className={css.toggle}
+          checked={prefs.openByDefault}
+          aria-label={t('settingsOpenTitle')}
+          onChange={event => { onToggle(event.currentTarget.checked) }}
+        />
+      </label>
+      <div className={css.row}>
+        <span className={css.rowText}>
+          <span className={css.title}>{t('settingsWidthTitle')}</span>
+          <span className={css.desc}>{t('settingsWidthDesc')}</span>
+        </span>
+        <span className={css.control}>
+          <Input
+            type="number"
+            className={css.percentInput}
+            value={widthDraft}
+            min={WIDTH_PERCENT_MIN}
+            max={WIDTH_PERCENT_MAX}
+            step={1}
+            aria-label={t('settingsWidthTitle')}
+            onChange={event => { setWidthDraft(event.currentTarget.value) }}
+            onBlur={commitWidth}
+            onKeyDown={event => {
+              if (event.key === 'Enter') event.currentTarget.blur()
+            }}
+          />
+          <span className={css.suffix}>{t('settingsWidthSuffix')}</span>
+        </span>
+      </div>
+      {error !== null && (
+        <div className={css.error} role="alert">
+          {error}
+        </div>
+      )}
+    </div>
+  )
+}

src/client/api.ts

@@ -119,6 +119,15 @@ export const api = {
    *  this explicit route). */
   ptyClose: (scope: SessionScope, tab: string) =>
     call<{ ok: true }>('pty.close', scopePayload(scope, { tab })),
+  /** Read the side card preferences (plugin-global, no session scope). */
+  settingsGet: () =>
+    call<{ value?: unknown; revision?: number }>('settings.get', {}),
+  /** Merge a patch into the side card preferences (revision-guarded). */
+  settingsUpdate: (patch: Record<string, unknown>, expectedRevision?: number) =>
+    call<{ value?: unknown; revision?: number }>('settings.update', {
+      patch,
+      ...(expectedRevision !== undefined ? { expectedRevision } : {}),
+    }),
 }
 
 /** Absolute URL of the media route for one path (images only). */

src/client/index.tsx

@@ -1,16 +1,22 @@
 /**
- * Client half of dsh-better-sidebar: mounts the right sidebar portal (inside
- * an error boundary so a rendering failure shows an error strip instead of a
- * blank panel) and registers the turn-tail interception. Requires the
- * runtime's slots and sessions services; the bundle itself is a module-table
- * consumer only (react + ui-primitives + xterm, all provided or inlined).
+ * Client half of dsh-better-sidebar: resolves the user's "Side card"
+ * preferences through the plugin's own fenced settings route, mounts the
+ * right sidebar portal (inside an error boundary so a rendering failure
+ * shows an error strip instead of a blank panel), registers the turn-tail
+ * interception, and contributes the Side card settings section to the DSH
+ * Settings shell. Requires the runtime's slots and sessions services; the
+ * bundle itself is a module-table consumer only (react + ui-primitives +
+ * xterm, all provided or inlined).
  */
 import { Component, createElement, type ErrorInfo, type ReactNode } from 'react'
-import { createRoot } from 'react-dom/client'
+import { createRoot, type Root } from 'react-dom/client'
 import type { Context } from '../context-types.ts'
 import { createSidebarStore } from './state.ts'
 import { Sidebar } from './Sidebar.tsx'
 import { registerTurnTailInterception } from './intercept.tsx'
+import { loadPrefs } from './prefs.ts'
+import { SideCardSection } from './SideCardSection.tsx'
+import { api } from './api.ts'
 import { t } from './locales.ts'
 import css from './sidebar.module.css'
 import './layout.css'
@@ -60,7 +66,7 @@ class SidebarBoundary extends Component<{ children: ReactNode }, { error: string
 export function apply(ctx: Context): void {
   // One store instance per activation: production code creates it only here,
   // then hands it to the mounted panel and closes over it in the slot
-  // registration (the official createXXXStore() factory rule — no
+  // registrations (the official createXXXStore() factory rule — no
   // module-level singleton).
   const sidebarStore = createSidebarStore()
   // A failure anywhere in the client lifecycle must never take the app down
@@ -81,19 +87,35 @@ export function apply(ctx: Context): void {
   }
   try {
     ctx.effect(() => {
-      try {
-        const host = document.createElement('div')
-        host.setAttribute('data-dsh-better-sidebar', '')
-        document.body.appendChild(host)
-        const root = createRoot(host)
-        root.render(createElement(SidebarBoundary, null, createElement(Sidebar, { ctx, store: sidebarStore })))
-        return () => {
-          root.unmount()
-          host.remove()
+      let disposed = false
+      let root: Root | undefined
+      let host: HTMLDivElement | undefined
+      void (async () => {
+        // Resolve the user's side card prefs BEFORE the first session seeds,
+        // so a brand-new conversation opens (or stays closed) at the chosen
+        // width from first paint. A settings route failure falls back to the
+        // schema defaults; the sidebar still mounts (a stalled wire gives up
+        // after the timeout and mounts on the defaults).
+        const prefs = await Promise.race([
+          loadPrefs(api),
+          new Promise<null>(resolve => { const timer = window.setTimeout(() => resolve(null), 2000) }),
+        ])
+        if (prefs !== null) sidebarStore.setPrefs(prefs)
+        if (disposed) return
+        try {
+          host = document.createElement('div')
+          host.setAttribute('data-dsh-better-sidebar', '')
+          document.body.appendChild(host)
+          root = createRoot(host)
+          root.render(createElement(SidebarBoundary, null, createElement(Sidebar, { ctx, store: sidebarStore })))
+        } catch (error) {
+          fail('mount', error)
         }
-      } catch (error) {
-        fail('mount', error)
-        return undefined
+      })()
+      return () => {
+        disposed = true
+        root?.unmount()
+        host?.remove()
       }
     }, 'dsh-better-sidebar: sidebar mount')
 
@@ -108,6 +130,18 @@ export function apply(ctx: Context): void {
       },
       'dsh-better-sidebar: turn-tail interception',
     )
+
+    // The "Side card" settings section: appears in the DSH Settings shell
+    // once the shell's declaration is on the ledger (slots.inject waits for
+    // it); the section reads/writes the prefs through the plugin's own
+    // fenced settings route and keeps the shared store in sync.
+    ctx.slots.inject('settings.section', () => ctx.slots.register({
+      name: 'settings.section',
+      id: 'better-sidebar',
+      order: 100,
+      label: () => t('settingsNav'),
+      inject: () => ({ store: sidebarStore }),
+    }, SideCardSection))
   } catch (error) {
     fail('load', error)
   }

src/client/locales.ts

@@ -70,6 +70,14 @@ const zh = {
   copyRelative: '复制相对地址',
   copyAbsolute: '复制绝对地址',
   download: '下载',
+  settingsNav: '侧边卡片',
+  settingsOpenTitle: '新会话默认打开',
+  settingsOpenDesc: '新建会话时自动展开侧边卡片；已存在的会话保持各自布局',
+  settingsWidthTitle: '默认宽度占比',
+  settingsWidthDesc: '新建会话时侧边卡片占窗口宽度的百分比 (20–60)',
+  settingsWidthSuffix: '%',
+  settingsSaveFailed: '保存失败',
+  settingsConflict: '设置已被其他窗口修改，请重试',
 }
 
 const en: Record<keyof typeof zh, string> = {
@@ -137,6 +145,14 @@ const en: Record<keyof typeof zh, string> = {
   copyRelative: 'Copy relative path',
   copyAbsolute: 'Copy absolute path',
   download: 'Download',
+  settingsNav: 'Side card',
+  settingsOpenTitle: 'Open by default for new conversations',
+  settingsOpenDesc: 'Expand the side card automatically for brand-new conversations; existing conversations keep their own layouts',
+  settingsWidthTitle: 'Default width share',
+  settingsWidthDesc: 'The side card\'s default share of the window width for new conversations (20–60)',
+  settingsWidthSuffix: '%',
+  settingsSaveFailed: 'Failed to save',
+  settingsConflict: 'The setting changed in another window — please retry',
 }
 
 /** Translate a copy key in the browser's language (zh → zh, else en). */

src/client/prefs.ts

@@ -0,0 +1,58 @@
+/**
+ * Client-side read of the user-facing "Side card" preferences. The host owns
+ * the namespace through the settings seam (in-process); the DSH settings RPC
+ * domain only serves allowlisted namespaces to configuration clients, so the
+ * client reads and writes THIS namespace through the plugin's own fenced
+ * /sidebar routes instead (api.settingsGet/settingsUpdate). Any failure
+ * (route rejected, namespace absent, a field of the wrong type, a value out
+ * of the contract range) falls back to the schema defaults — the side card
+ * must keep working exactly as composed when the settings surface is missing.
+ */
+import type { api } from './api.ts'
+import {
+  clampWidthPercent,
+  SIDEBAR_PREFS_DEFAULTS,
+  type SidebarPrefs,
+} from '../prefs-shared.ts'
+
+export { SIDEBAR_PREFS_DEFAULTS, clampWidthPercent }
+export type { SidebarPrefs }
+
+/** The settings wire face the preferences need (a subset of the plugin api). */
+export type SidebarSettingsClient = Pick<typeof api, 'settingsGet' | 'settingsUpdate'>
+
+/**
+ * Validate one raw resolved value into {@link SidebarPrefs}. Used for the
+ * settings.get payload AND the settings.update response (both carry the
+ * layered resolved value); any malformed field falls back to its default.
+ * @param value - the raw resolved section from the settings wire.
+ * @returns validated prefs (always well-formed).
+ */
+export function parsePrefs(value: unknown): SidebarPrefs {
+  if (value === null || typeof value !== 'object') return { ...SIDEBAR_PREFS_DEFAULTS }
+  const record = value as Record<string, unknown>
+  return {
+    openByDefault: typeof record.openByDefault === 'boolean'
+      ? record.openByDefault
+      : SIDEBAR_PREFS_DEFAULTS.openByDefault,
+    defaultWidthPercent: typeof record.defaultWidthPercent === 'number' && Number.isFinite(record.defaultWidthPercent)
+      ? clampWidthPercent(record.defaultWidthPercent)
+      : SIDEBAR_PREFS_DEFAULTS.defaultWidthPercent,
+  }
+}
+
+/**
+ * Read the resolved side card preferences through the plugin's settings route.
+ * @param settings - the settings wire face (the plugin api by default).
+ * @returns validated prefs, or the schema defaults when the route rejects,
+ * the namespace is absent, or a stored value violates the contract.
+ */
+export async function loadPrefs(settings: SidebarSettingsClient): Promise<SidebarPrefs> {
+  try {
+    const view = await settings.settingsGet()
+    return parsePrefs(view.value)
+  } catch {
+    // Transport/fence rejection or a malformed response: keep the defaults.
+    return { ...SIDEBAR_PREFS_DEFAULTS }
+  }
+}

src/client/sidebar.module.css

@@ -1,9 +1,11 @@
 /**
  * Sidebar styles. Per the DSH web-styling rules every visual value rides the
  * theme: --dsw-alias-* semantic tokens for colors, --dsw-font-* typography
- * roles (size paired with line-height), --dsw-shadow-* for elevation, and
- * --ds-* for motion. No static palette values, no color literals, no theme
- * selectors — light/dark adaptation is the theme package's job.
+ * roles (size paired with line-height), and --ds-* for motion. The chrome
+ * mirrors the native DSH sidebar: flat (NO box-shadows anywhere), the
+ * sidebar fill surface, hairline borders, and the 28/36px circular icon
+ * controls with hover fills. No static palette values, no color literals, no
+ * theme selectors — light/dark adaptation is the theme package's job.
  */
 
 /* ── Shell ─────────────────────────────────────────────────────────────── */
@@ -16,28 +18,31 @@
   z-index: 55;
   display: flex;
   align-items: center;
+  /* Native rail inset: the 36px control sits 10px off the column edge. */
+  padding: 0 10px;
 }
 
+/* The closed-state affordance is the native rail icon control: a plain 36px
+   circle, transparent fill, secondary ink; hover raises the fill. No border,
+   no shadow — the icon alone is the affordance (SidebarRoot .iconButton). */
 .toggleButton {
   display: flex;
   align-items: center;
   justify-content: center;
-  width: 26px;
-  height: 64px;
-  border: 1px solid var(--dsw-alias-border-l2-darkmode-thin);
-  border-right: none;
-  border-radius: 10px 0 0 10px;
-  background: var(--dsw-alias-button-floating-fill);
+  width: 36px;
+  height: 36px;
+  border: none;
+  border-radius: 50%;
+  background: transparent;
   color: var(--dsw-alias-label-secondary);
   cursor: pointer;
-  box-shadow: var(--dsw-shadow-lv1);
   transition:
     background var(--ds-transition-duration-slow) var(--ds-ease-in-out),
     color var(--ds-transition-duration-slow) var(--ds-ease-in-out);
 }
 
 .toggleButton:hover:not(:disabled) {
-  background: var(--dsw-alias-button-floating-hover);
+  background: var(--dsw-alias-interactive-bg-hover);
   color: var(--dsw-alias-label-primary);
 }
 
@@ -54,9 +59,10 @@
   z-index: 50;
   display: flex;
   flex-direction: column;
-  background: var(--dsw-alias-bg-layer-1);
+  /* The native sidebar surface: bluish-50 over white / bluish-900 over dark,
+     exactly like the app's own sidebar column (SidebarRoot .root). */
+  background: var(--dsw-specific-sidebar-fill);
   border-left: 1px solid var(--dsw-alias-border-l2);
-  box-shadow: var(--dsw-shadow-lv2);
   /* Expand/collapse slides the panel; fullscreen animates the width. */
   transition:
     transform var(--ds-transition-duration-slow) var(--ds-ease-in-out),
@@ -67,7 +73,6 @@
 .panelHidden {
   transform: translateX(102%);
   pointer-events: none;
-  box-shadow: none;
   visibility: hidden;
   transition:
     transform var(--ds-transition-duration-slow) var(--ds-ease-in-out),
@@ -107,7 +112,7 @@
 }
 
 .panelTitle {
-  font: var(--dsw-font-xxs-strong-12);
+  font: var(--dsw-font-s-14);
   color: var(--dsw-alias-label-secondary);
   overflow: hidden;
   text-overflow: ellipsis;
@@ -371,8 +376,8 @@
 
 .tabActive {
   color: var(--dsw-alias-label-primary);
-  background: var(--dsw-alias-bg-base);
-  box-shadow: inset 0 -2px 0 var(--dsw-alias-brand-primary);
+  /* Native selected fill (Rows .sessionRow.selected) — no underline, no shadow. */
+  background: var(--dsw-alias-interactive-bg-active);
 }
 
 .tabTitle {
@@ -449,7 +454,7 @@
 }
 
 .explorerRoot {
-  font: var(--dsw-font-xxs-strong-12);
+  font: var(--dsw-font-s-14);
   color: var(--dsw-alias-label-secondary);
   overflow: hidden;
   text-overflow: ellipsis;
@@ -463,9 +468,9 @@
   padding: 2px 6px 8px;
 }
 
-/* One tree row: the app's tree-row cell (34px, radius 8, inset, hover
-   fill, 22px indent step) with a mount fade so expanding a directory
-   reveals its children gently (stable keys keep existing rows from
+/* One tree row: the app's session-row cell (34px, radius 8, inset, hover
+   fill, 22px indent step, 14px ink) with a mount fade so expanding a
+   directory reveals its children gently (stable keys keep existing rows from
    replaying it). */
 .explorerRow {
   display: flex;
@@ -473,10 +478,10 @@
   gap: 6px;
   width: 100%;
   height: 34px;
-  padding: 0 6px;
+  padding: 0 8px;
   border: none;
   background: transparent;
-  font: var(--dsw-font-xxs-12);
+  font: var(--dsw-font-s-14);
   color: var(--dsw-alias-label-primary);
   text-align: left;
   cursor: pointer;
@@ -490,7 +495,7 @@
 }
 
 .explorerDir {
-  font: var(--dsw-font-xxs-strong-12);
+  font: var(--dsw-font-s-strong-14);
 }
 
 .explorerHidden {
@@ -843,7 +848,7 @@
   gap: 6px;
   min-height: 34px;
   margin: 0 6px;
-  padding: 0 6px 0 12px;
+  padding: 0 8px;
   border-radius: 8px;
   animation: dsh-row-in 150ms var(--ds-ease-in-out);
 }
@@ -888,7 +893,7 @@
   overflow: hidden;
   text-overflow: ellipsis;
   white-space: nowrap;
-  font: var(--dsw-font-xxs-12);
+  font: var(--dsw-font-s-14);
   color: var(--dsw-alias-label-primary);
 }
 

src/client/state.ts

@@ -9,6 +9,8 @@
  * divides the space row- or column-wise with fractional sizes. All tree
  * operations are pure functions over the node, unit-tested in tests/state.spec.ts.
  */
+import { SIDEBAR_PREFS_DEFAULTS, type SidebarPrefs } from '../prefs-shared.ts'
+
 export type TabType = 'explorer' | 'git' | 'editor' | 'terminal'
 
 /** One open tab. `path` carries the file (editor) or is absent (explorer/git). */
@@ -54,8 +56,6 @@ export interface SidebarState {
 export const PANEL_MIN = 280
 export const PANEL_MAX = 640
 export const PANEL_DEFAULT = 400
-/** Approximate default width of the host's left sidebar (columns.ts SIDEBAR_DEFAULT). */
-export const LEFT_SIDEBAR_DEFAULT = 320
 export const TAB_MAX_WIDTH = 160
 export const TERMINAL_LIMIT = 3
 
@@ -99,15 +99,16 @@ function maxCounterId(parsed: unknown): number {
   return max
 }
 
-/** A fresh default state: open, one explorer tab in one pane. `width` is
- * the caller's preferred panel width (default PANEL_DEFAULT); the store
- * seeds new sessions with half the viewport. */
-export function makeDefaultState(width = PANEL_DEFAULT): SidebarState {
+/** A fresh default state: one explorer tab in one pane, open per the caller's
+ * preference. `width` is the caller's preferred panel width (default
+ * PANEL_DEFAULT) and `panelOpen` whether the panel starts expanded (default
+ * true); the store seeds new sessions from the user's side card prefs. */
+export function makeDefaultState(width = PANEL_DEFAULT, panelOpen = true): SidebarState {
   const leaf: SidebarLeaf = { kind: 'leaf', id: uid('pane'), tabs: [], active: null }
   leaf.tabs = [{ id: uid('tab'), type: 'explorer', title: 'Explorer' }]
   leaf.active = leaf.tabs[0]!.id
   return {
-    panelOpen: true,
+    panelOpen,
     width,
     activePane: leaf.id,
     nextTerminal: 1,
@@ -405,7 +406,14 @@ export interface SidebarSnapshot {
   state: SidebarState | undefined
 }
 
-function loadState(sessionId: string): SidebarState {
+/** Default panel width for one viewport: the prefs percent of the window,
+ * clamped to the panel floor (a tiny percent must stay usable) and to the
+ * viewport (a large one must never cover the whole window). */
+export function defaultWidthFor(viewport: number, percent: number): number {
+  return Math.min(viewport, Math.max(PANEL_MIN, Math.round(viewport * percent / 100)))
+}
+
+function loadState(sessionId: string, prefs: SidebarPrefs): SidebarState {
   try {
     const raw = localStorage.getItem(`${STORAGE_PREFIX}:${sessionId}`)
     if (raw !== null) {
@@ -419,13 +427,15 @@ function loadState(sessionId: string): SidebarState {
   } catch {
     // Corrupt or unavailable storage: fall through to the default.
   }
-  // New sessions open at half the CONTENT area (the viewport minus the
-  // left sidebar's default width), so the panel never swallows half the
-  // whole window; the same default applies to every session.
-  const contentHalf = typeof window !== 'undefined'
-    ? Math.max(PANEL_MIN, Math.round((window.innerWidth - LEFT_SIDEBAR_DEFAULT) / 2))
-    : PANEL_DEFAULT
-  return makeDefaultState(contentHalf)
+  // New sessions seed from the user's side card prefs: the width is the
+  // chosen percent of the window (clamped to the panel floor and the
+  // viewport so a huge percent can never crush the app shell), and the
+  // panel starts open only when the preference says so.
+  const viewport = typeof window !== 'undefined' ? window.innerWidth : undefined
+  const width = viewport === undefined
+    ? PANEL_DEFAULT
+    : defaultWidthFor(viewport, prefs.defaultWidthPercent)
+  return makeDefaultState(width, prefs.openByDefault)
 }
 
 /**
@@ -537,6 +547,18 @@ export class SidebarStore {
   private snapshot: SidebarSnapshot = { sessionId: undefined, state: undefined }
   private readonly listeners = new Set<() => void>()
   private persistTimer: number | undefined
+  /** User-facing side card prefs seeding brand-new session states (defaults until the settings RPC resolves). */
+  private prefs: SidebarPrefs = { ...SIDEBAR_PREFS_DEFAULTS }
+
+  /** Replace the side card prefs (the settings RPC result / settings page write). */
+  setPrefs(prefs: SidebarPrefs): void {
+    this.prefs = { ...prefs }
+  }
+
+  /** The current side card prefs (seeds new sessions; persisted states win). */
+  getPrefs(): SidebarPrefs {
+    return { ...this.prefs }
+  }
 
   /** Select a session (or none); loads its persisted state. */
   setSession(sessionId: string | undefined): void {
@@ -546,7 +568,7 @@ export class SidebarStore {
     } else {
       let state = this.bySession.get(sessionId)
       if (state === undefined) {
-        state = loadState(sessionId)
+        state = loadState(sessionId, this.prefs)
         this.bySession.set(sessionId, state)
       } else {
         // Cache hit: another session's load/ops may have left the uid

src/config.ts

@@ -6,6 +6,23 @@
  */
 
 import z from 'schemastery'
+import {
+  SIDEBAR_PREFS_DEFAULTS,
+  SIDEBAR_PREFS_NS,
+  WIDTH_PERCENT_DEFAULT,
+  WIDTH_PERCENT_MAX,
+  WIDTH_PERCENT_MIN,
+  type SidebarPrefs,
+} from './prefs-shared.ts'
+
+export {
+  SIDEBAR_PREFS_DEFAULTS,
+  SIDEBAR_PREFS_NS,
+  WIDTH_PERCENT_DEFAULT,
+  WIDTH_PERCENT_MAX,
+  WIDTH_PERCENT_MIN,
+  type SidebarPrefs,
+} from './prefs-shared.ts'
 
 /** Tunable sidebar host limits (every field optional; defaults fill in). */
 export interface SidebarConfig {
@@ -54,3 +71,11 @@ export function resolveSidebarConfig(config: SidebarConfig | undefined): Resolve
     reconnectGraceMs: config?.reconnectGraceMs ?? 30_000,
   }
 }
+
+// ── User-facing "Side card" preferences ─────────────────────────────────────
+
+/** Schemastery schema for the user-facing preferences (validated by the settings service). */
+export const PrefsSchema: z<SidebarPrefs> = z.object({
+  openByDefault: z.boolean().default(true),
+  defaultWidthPercent: z.number().step(1).min(WIDTH_PERCENT_MIN).max(WIDTH_PERCENT_MAX).default(WIDTH_PERCENT_DEFAULT),
+})

src/context-types.ts

@@ -80,6 +80,12 @@ export interface SidebarSlotRegisterOptions {
 /** The client slots service face (register returns the disposer). */
 export interface SidebarSlotsService {
   register(options: SidebarSlotRegisterOptions, component: unknown): () => void
+  /**
+   * Run a callback for each declaration lifetime of a slot (the runtime
+   * SlotsService.inject): a no-op while the slot is undeclared, so the
+   * settings section registration waits for the settings shell.
+   */
+  inject(key: string, callback: () => () => void): () => void
 }
 
 /** The client session list row the sidebar reads (cwd for the explorer). */
@@ -139,12 +145,42 @@ export interface SidebarInvariantsService {
   ): () => void
 }
 
+/** The settings service face (mirror of @deepseek-ai/dsh-settings' Settings). */
+export interface SidebarSettingsService {
+  /**
+   * Register one namespace schema (the resolved value layers schema defaults,
+   * then the composition base, then the user document).
+   */
+  register<T>(
+    ns: string,
+    schema: unknown,
+    options?: { base?: Partial<T>; applies?: 'live' | 'restart' },
+  ): {
+    get(): T
+    watch(callback: (next: T, prev: T) => void | Promise<void>): () => void
+    update(patch: object): Promise<void>
+    replace(section: object): Promise<void>
+  }
+  /** Redacted descriptors of every registered namespace (secrets stripped). */
+  describe(options?: { redactSecrets?: boolean }): Array<{
+    ns: string
+    value?: unknown
+    base?: unknown
+    user?: unknown
+    applies: 'live' | 'restart'
+    revision: number
+  }>
+  /** Service-level merge write with the revision guard (a stale writer is refused). */
+  update(ns: string, patch: object, expectedRevision?: number): Promise<void>
+}
+
 declare module 'cordis' {
   interface Context {
     httpServer: SidebarHttpServer
     sessions: SidebarSessionStore & SidebarSessionsService
     loader: SidebarLoader
     slots: SidebarSlotsService
+    settings: SidebarSettingsService
     invariants: SidebarInvariantsService
     /**
      * Register a lifecycle callback (DSH-vendored cordis): runs at plugin

src/index.ts

@@ -18,13 +18,16 @@ import { WebSocket, WebSocketServer } from 'ws'
 import type { Context } from './context-types.ts'
 import {
   Config,
+  PrefsSchema,
   resolveSidebarConfig,
+  SIDEBAR_PREFS_NS,
   type ResolvedSidebarConfig,
   type SidebarConfig,
 } from './config.ts'
 import { isWithin, parentOf, requireAbsolute, listDirectory, rootLabel } from './fs-tree.ts'
 import { isTrustedApiRequest } from './trust-fence.ts'
 import * as git from './git.ts'
+import { SettingsConflictError, settingsNamespace, type SettingsNamespace } from '@deepseek-ai/dsh-settings'
 import { defaultShell, ensureSpawnHelper, PtyManager } from './pty-manager.ts'
 import { readJsonBody, requireString, SidebarError, writeError, writeJson, writeOk } from './wire.ts'
 
@@ -112,8 +115,27 @@ async function readText(path: string, readLimit: number): Promise<{ content: str
 /** One API method dispatch table entry. */
 type ApiMethod = (payload: unknown) => Promise<unknown> | unknown
 
+/**
+ * The live face of the side card settings namespace, bound to the settings
+ * service when it is mounted. The DSH settings RPC domain only serves
+ * allowlisted namespaces (api-proxy exposedNamespaces), so the client reads
+ * and writes THIS namespace through the plugin's own fenced /sidebar routes,
+ * which call the seam in-process — no configuration-client gate involved.
+ */
+export interface SidebarSettingsFace {
+  /** The current resolved value + revision (undefined while the settings service is absent). */
+  get(): { value?: unknown; revision?: number }
+  /** Merge a patch (revision-guarded) and return the fresh resolved view. */
+  update(patch: Record<string, unknown>, expectedRevision?: number): Promise<{ value?: unknown; revision?: number }>
+}
+
 /** Build the API method table bound to the plugin context, pty manager, and resolved config. */
-function buildApi(ctx: Context, ptyManager: PtyManager, resolved: ResolvedSidebarConfig): Record<string, ApiMethod> {
+function buildApi(
+  ctx: Context,
+  ptyManager: PtyManager,
+  resolved: ResolvedSidebarConfig,
+  getSettings: () => SidebarSettingsFace | undefined,
+): Record<string, ApiMethod> {
   const cwdOf = (payload: unknown): { sessionId: string; cwd: string } => {
     const sessionId = requireString(payload, 'sessionId')
     const record = payload as { cwd?: unknown } | null
@@ -212,6 +234,35 @@ function buildApi(ctx: Context, ptyManager: PtyManager, resolved: ResolvedSideba
       ptyManager.close(`${sessionId}:${tab}`)
       return { ok: true }
     },
+    // The side card preferences. The settings service is optional in the
+    // composition; while absent the routes report undefined and the client
+    // keeps the schema defaults. Writes are revision-guarded: a stale editor
+    // is refused with settings-conflict so a concurrent change is never
+    // silently overwritten (mirror of the settings seam's own guard).
+    'settings.get': () => {
+      const settings = getSettings()
+      return settings?.get() ?? { value: undefined, revision: undefined }
+    },
+    'settings.update': async (payload) => {
+      const settings = getSettings()
+      if (settings === undefined) {
+        throw new SidebarError('settings-rejected', 'the settings service is not mounted in this deployment', 503)
+      }
+      const record = payload as { patch?: unknown; expectedRevision?: unknown } | null
+      const patch = record?.patch
+      if (patch === null || typeof patch !== 'object' || Array.isArray(patch)) {
+        throw new SidebarError('bad-request', 'patch must be a plain object')
+      }
+      const expectedRevision = typeof record?.expectedRevision === 'number' ? record.expectedRevision : undefined
+      try {
+        return await settings.update(patch as Record<string, unknown>, expectedRevision)
+      } catch (error) {
+        if (error instanceof SettingsConflictError) {
+          throw new SidebarError('settings-conflict', error.message, 409)
+        }
+        throw new SidebarError('settings-rejected', error instanceof Error ? error.message : String(error), 400)
+      }
+    },
   }
 }
 
@@ -231,8 +282,35 @@ export function apply(ctx: Context, config?: SidebarConfig): void {
   const fence = (req: IncomingMessage): boolean => isTrustedApiRequest(req, trustedHosts)
   const ptyManager = new PtyManager(defaultShell(), resolved.terminalsPerSession)
 
+  // ── User-facing "Side card" preferences ──────────────────────────────────
+  // Register the namespace with the settings provider so the Settings page
+  // (client half) can render and persist the new-conversation defaults. The
+  // DSH settings RPC domain (api-proxy) only serves allowlisted namespaces to
+  // configuration clients, so the client reaches this namespace through the
+  // plugin's own fenced routes below ('settings.get'/'settings.update'),
+  // which call the seam in-process. Deployments without a settings service
+  // simply never fill the face and the client falls back to the defaults.
+  let settingsFace: SidebarSettingsFace | undefined
+  ctx.inject(['settings'], (sctx) => {
+    const ns: SettingsNamespace = settingsNamespace(SIDEBAR_PREFS_NS)
+    sctx.settings.register(ns, PrefsSchema)
+    const viewOf = (): { value?: unknown; revision?: number } => {
+      const descriptor = sctx.settings.describe({ redactSecrets: true }).find(candidate => candidate.ns === ns)
+      return descriptor === undefined
+        ? { value: undefined, revision: undefined }
+        : { value: descriptor.value, revision: descriptor.revision }
+    }
+    settingsFace = {
+      get: viewOf,
+      update: async (patch, expectedRevision) => {
+        await sctx.settings.update(ns, patch, expectedRevision)
+        return viewOf()
+      },
+    }
+  })
+
   // ── JSON API ────────────────────────────────────────────────────────────
-  const api = buildApi(ctx, ptyManager, resolved)
+  const api = buildApi(ctx, ptyManager, resolved, () => settingsFace)
   ctx.effect(() => ctx.httpServer.register({
     kind: 'prefix',
     path: '/sidebar/api',

src/prefs-shared.ts

@@ -0,0 +1,34 @@
+/**
+ * Shared "Side card" preference vocabulary (types + constants), consumed by
+ * BOTH halves: the host registers the schemastery schema over these values
+ * (config.ts) and the client reads/writes them through the settings RPC
+ * (client/prefs.ts, client/SideCardSection.tsx). Kept free of schemastery so
+ * the browser bundle never pulls the schema runtime in.
+ */
+
+/** The user-settings namespace holding the side card preferences. */
+export const SIDEBAR_PREFS_NS = 'dsh-better-sidebar'
+
+/** User-facing side card preferences (new-conversation defaults). */
+export interface SidebarPrefs {
+  /** Whether a brand-new conversation opens the side card by default. */
+  openByDefault: boolean
+  /** Default panel width as a percent of the window width (20–60). */
+  defaultWidthPercent: number
+}
+
+/** Range contract of {@link SidebarPrefs.defaultWidthPercent}. */
+export const WIDTH_PERCENT_MIN = 20
+export const WIDTH_PERCENT_MAX = 60
+export const WIDTH_PERCENT_DEFAULT = 30
+
+/** Fallback prefs used whenever the settings document is unreachable or malformed. */
+export const SIDEBAR_PREFS_DEFAULTS: SidebarPrefs = {
+  openByDefault: true,
+  defaultWidthPercent: WIDTH_PERCENT_DEFAULT,
+}
+
+/** Clamp one width percent into the contract range (shared by schema and client reads). */
+export function clampWidthPercent(value: number): number {
+  return Math.min(WIDTH_PERCENT_MAX, Math.max(WIDTH_PERCENT_MIN, Math.round(value)))
+}

src/wire.ts

@@ -15,6 +15,8 @@ export type SidebarErrorCode =
   | 'fs-error'
   | 'git-error'
   | 'pty-error'
+  | 'settings-rejected'
+  | 'settings-conflict'
   | 'internal'
 
 /** One API failure with its wire code and HTTP status. */

tests/plugin-shape.spec.ts

@@ -35,4 +35,20 @@ describe('dsh-better-sidebar plugin export shape', () => {
     expect(resolved.terminalsPerSession).toBe(3)
     expect(resolved.reconnectGraceMs).toBe(30_000)
   })
+
+  it('registers the side card preferences schema with the documented defaults', async () => {
+    const { PrefsSchema, SIDEBAR_PREFS_NS } = await import('../src/config.ts')
+    expect(SIDEBAR_PREFS_NS).toBe('dsh-better-sidebar')
+    const resolved = (PrefsSchema as unknown as {
+      (input: Record<string, unknown> | undefined): Record<string, unknown>
+    })(undefined)
+    expect(resolved.openByDefault).toBe(true)
+    expect(resolved.defaultWidthPercent).toBe(30)
+    // A stored overridden value resolves through (the range contract is
+    // enforced by the settings service on write).
+    const overridden = (PrefsSchema as unknown as {
+      (input: Record<string, unknown> | undefined): Record<string, unknown>
+    })({ openByDefault: false, defaultWidthPercent: 45 })
+    expect(overridden).toEqual({ openByDefault: false, defaultWidthPercent: 45 })
+  })
 })

tests/smoke.spec.ts

@@ -6,6 +6,7 @@
 import { describe, expect, it } from 'vitest'
 import { tmpdir } from 'node:os'
 import { resolve as resolvePath } from 'node:path'
+import { SettingsConflictError, settingsNamespace } from '@deepseek-ai/dsh-settings'
 import { apply } from '../src/index.ts'
 import * as git from '../src/git.ts'
 import { listDirectory } from '../src/fs-tree.ts'
@@ -20,6 +21,9 @@ interface FakeContext {
   }
   sessions: { get: (id: string) => { header: { cwd?: string } } | undefined }
   effect: (fn: () => void | (() => void), label?: string) => void
+  /** The settings service never appears in the smoke context: the inject
+   *  callback must never run (mirror of cordis' service-less inject). */
+  inject: (deps: readonly string[], callback: (sctx: never) => void) => () => void
 }
 
 describe('host plugin smoke', () => {
@@ -40,6 +44,9 @@ describe('host plugin smoke', () => {
         const cleanup = fn()
         if (typeof cleanup === 'function') effects.push(cleanup)
       },
+      // No settings service in the smoke context: the registration callback
+      // never runs (cordis' service-less inject behaves the same).
+      inject: () => () => {},
     }
     apply(ctx as never)
     expect(routes.map(route => route.path)).toEqual(['/sidebar/api', '/sidebar/file'])
@@ -167,6 +174,8 @@ describe('session cwd resolution over the API route', () => {
       sessions: overrides.sessions ?? { get: () => undefined },
       // The vendored cordis runs registration effects immediately.
       effect: (fn: () => void | (() => void)) => { fn() },
+      // No settings service: the namespace registration never runs.
+      inject: () => () => {},
     }
     apply(ctx as never)
     return routes.find(route => route.path === '/sidebar/api')!
@@ -235,3 +244,122 @@ describe('session cwd resolution over the API route', () => {
     expect(missing.ok).toBe(false)
   })
 })
+
+describe('side card settings routes', () => {
+  /** A minimal settings seam: register/describe/update with the revision guard. */
+  const createFakeSettings = () => {
+    const namespaces = new Map<string, {
+      schema: unknown
+      value: Record<string, unknown> | undefined
+      revision: number
+    }>()
+    const resolve = (entry: { schema: unknown; value: Record<string, unknown> | undefined }): unknown => {
+      const schema = entry.schema as (input: unknown) => unknown
+      return entry.value === undefined ? schema(undefined) : schema(entry.value)
+    }
+    return {
+      register(ns: string, schema: unknown) {
+        namespaces.set(ns, { schema, value: undefined, revision: 0 })
+        return { get: () => ({}), watch: () => () => {}, update: async () => {}, replace: async () => {} }
+      },
+      describe() {
+        return [...namespaces.entries()].map(([ns, entry]) => ({
+          ns,
+          value: resolve(entry),
+          applies: 'live' as const,
+          revision: entry.revision,
+        }))
+      },
+      async update(ns: string, patch: Record<string, unknown>, expectedRevision?: number) {
+        const entry = namespaces.get(ns)
+        if (entry === undefined) throw new Error(`settings namespace "${ns}" is not registered`)
+        if (expectedRevision !== undefined && expectedRevision !== entry.revision) {
+          throw new SettingsConflictError(settingsNamespace(ns), expectedRevision, entry.revision)
+        }
+        entry.value = { ...entry.value, ...patch }
+        entry.revision += 1
+      },
+    }
+  }
+
+  const mountWithSettings = (settings?: unknown): SidebarWebRoute => {
+    const routes: SidebarWebRoute[] = []
+    const ctx = {
+      loader: { entries: () => [] },
+      httpServer: {
+        register: (route: SidebarWebRoute) => { routes.push(route); return () => {} },
+        registerUpgrade: (route: SidebarWebUpgradeRoute) => { void route; return () => {} },
+      },
+      sessions: { get: () => undefined },
+      effect: (fn: () => void | (() => void)) => { fn() },
+      inject: (deps: string[], callback: (sctx: { settings: unknown }) => void) => {
+        if (deps.includes('settings') && settings !== undefined) callback({ settings })
+        return () => {}
+      },
+    }
+    apply(ctx as never)
+    return routes.find(route => route.path === '/sidebar/api')!
+  }
+
+  const invoke = async (route: SidebarWebRoute, method: string, payload: unknown): Promise<{
+    ok: boolean
+    value?: unknown
+    error?: { code?: string; message: string }
+  }> => {
+    const body = Buffer.from(JSON.stringify(payload))
+    const req = {
+      method: 'POST',
+      url: `/sidebar/api/${method}`,
+      headers: { host: '127.0.0.1:3080' },
+      [Symbol.asyncIterator]: async function* () { yield body },
+    } as never
+    const out: { status: number; body: string } = { status: 200, body: '' }
+    const res = {
+      writeHead: (status: number) => { out.status = status },
+      end: (chunk: unknown) => { out.body += String(chunk ?? '') },
+    } as never
+    await route.handler(req, res)
+    return JSON.parse(out.body) as { ok: boolean; value?: unknown; error?: { code?: string; message: string } }
+  }
+
+  it('serves the schema defaults when the settings service is absent', async () => {
+    const route = mountWithSettings(undefined)
+    const result = await invoke(route, 'settings.get', {})
+    expect(result.ok).toBe(true)
+    expect(result.value).toEqual({ value: undefined, revision: undefined })
+  })
+
+  it('reads the resolved prefs and writes a patch through the seam', async () => {
+    const route = mountWithSettings(createFakeSettings())
+    const read = await invoke(route, 'settings.get', {})
+    expect(read.ok).toBe(true)
+    expect(read.value).toEqual({ value: { openByDefault: true, defaultWidthPercent: 30 }, revision: 0 })
+
+    const written = await invoke(route, 'settings.update', { patch: { openByDefault: false } })
+    expect(written.ok).toBe(true)
+    const view = written.value as { value: { openByDefault: boolean; defaultWidthPercent: number }; revision: number }
+    expect(view.value.openByDefault).toBe(false)
+    expect(view.value.defaultWidthPercent).toBe(30)
+    expect(view.revision).toBe(1)
+  })
+
+  it('refuses a stale write with settings-conflict (409)', async () => {
+    const route = mountWithSettings(createFakeSettings())
+    await invoke(route, 'settings.update', { patch: { openByDefault: false } })
+    // The second write carries the pre-write revision: the seam refuses it.
+    const stale = await invoke(route, 'settings.update', {
+      patch: { defaultWidthPercent: 40 },
+      expectedRevision: 0,
+    })
+    expect(stale.ok).toBe(false)
+    expect(stale.error?.code).toBe('settings-conflict')
+    expect(stale.error?.message).toMatch(/changed since it was read/)
+  })
+
+  it('rejects a non-object patch as bad-request', async () => {
+    const route = mountWithSettings(createFakeSettings())
+    const result = await invoke(route, 'settings.update', { patch: 'nope' })
+    expect(result.ok).toBe(false)
+    expect(result.error?.message).toMatch(/plain object/)
+  })
+})

tests/unit.spec.ts

@@ -2,10 +2,12 @@ import { describe, expect, it } from 'vitest'
 import { compareEntries, isWithin, parentOf, rootLabel, requireAbsolute } from '../src/fs-tree.ts'
 import { parseLogLines, parsePorcelainZ } from '../src/git.ts'
 import {
-  activateTab, allLeaves, closeTab, insertLeafAt, makeDefaultState, moveTab, moveTabToEdge,
-  openTab, resizeSplit, sanitizeState, splitPane, tabOpenIn, toggleExpanded,
+  activateTab, allLeaves, closeTab, createSidebarStore, defaultWidthFor, insertLeafAt, makeDefaultState,
+  moveTab, moveTabToEdge, openTab, resizeSplit, sanitizeState, splitPane, tabOpenIn, toggleExpanded,
   type SidebarState, type SplitNode,
 } from '../src/client/state.ts'
+import { loadPrefs, type SidebarSettingsClient } from '../src/client/prefs.ts'
+import { SIDEBAR_PREFS_DEFAULTS } from '../src/prefs-shared.ts'
 import { extOf, languageKeyForExt } from '../src/client/lang.ts'
 import { relativeTo } from '../src/client/paths.ts'
 import { producedForClosing, resolveSidebarPath, selectProducedFiles } from '../src/client/produced-files.ts'
@@ -450,3 +452,64 @@ describe('editor language mapping', () => {
     expect(languageKeyForExt('')).toBeNull()
   })
 })
+
+describe('side card preferences', () => {
+  /** A fake settings wire face whose settingsGet resolves to one raw value. */
+  const wire = (value: unknown): SidebarSettingsClient => ({
+    settingsGet: async () => ({ value, revision: 1 }),
+    settingsUpdate: async () => ({ value, revision: 2 }),
+  })
+
+  const rejecting = (): SidebarSettingsClient => ({
+    settingsGet: async () => { throw new Error('route rejected') },
+    settingsUpdate: async () => { throw new Error('route rejected') },
+  })
+
+  it('falls back to the defaults when the settings route rejects', async () => {
+    expect(await loadPrefs(rejecting())).toEqual(SIDEBAR_PREFS_DEFAULTS)
+  })
+
+  it('falls back to the defaults when the value is absent or malformed', async () => {
+    expect(await loadPrefs(wire(undefined))).toEqual(SIDEBAR_PREFS_DEFAULTS)
+    expect(await loadPrefs(wire('garbage'))).toEqual(SIDEBAR_PREFS_DEFAULTS)
+  })
+
+  it('parses a valid value and clamps the percent into the contract range', async () => {
+    expect(await loadPrefs(wire({ openByDefault: false, defaultWidthPercent: 80 })))
+      .toEqual({ openByDefault: false, defaultWidthPercent: 60 })
+  })
+
+  it('falls back per-field when a stored field is malformed', async () => {
+    expect(await loadPrefs(wire({ openByDefault: 'yes', defaultWidthPercent: 33 })))
+      .toEqual({ openByDefault: true, defaultWidthPercent: 33 })
+  })
+
+  it('seeds new-session defaults from the store prefs (open flag + width)', () => {
+    const store = createSidebarStore()
+    // Node environment: no window → the width falls back to PANEL_DEFAULT,
+    // while the open flag still follows the preference.
+    store.setPrefs({ openByDefault: false, defaultWidthPercent: 45 })
+    store.setSession('fresh-session')
+    expect(store.getPrefs()).toEqual({ openByDefault: false, defaultWidthPercent: 45 })
+    const snapshot = store.getSnapshot()
+    expect(snapshot.sessionId).toBe('fresh-session')
+    expect(snapshot.state?.panelOpen).toBe(false)
+    expect(snapshot.state?.width).toBe(400)
+    // The default prefs keep the panel open.
+    const openStore = createSidebarStore()
+    openStore.setSession('another-fresh')
+    expect(openStore.getSnapshot().state?.panelOpen).toBe(true)
+  })
+
+  it('derives the default width from the window percent with clamps', () => {
+    expect(defaultWidthFor(1440, 30)).toBe(432)
+    expect(defaultWidthFor(800, 30)).toBe(280) // the panel floor
+    expect(defaultWidthFor(1440, 100)).toBe(1440) // the viewport cap
+  })
+
+  it('makeDefaultState honors the open flag', () => {
+    expect(makeDefaultState().panelOpen).toBe(true)
+    expect(makeDefaultState(400, false).panelOpen).toBe(false)
+    expect(makeDefaultState(400, false).width).toBe(400)
+  })
+})