diff --git a/app/shared/src/styles/tokens-base.css b/app/shared/src/styles/tokens-base.css
index a98ccb72b..37defe8d7 100644
--- a/app/shared/src/styles/tokens-base.css
+++ b/app/shared/src/styles/tokens-base.css
@@ -419,12 +419,16 @@
 }
 
 /* ── Global Reset ──────────────────────────────────────────────────── */
-*,
-*::before,
-*::after {
-  box-sizing: border-box;
-  margin: 0;
-  padding: 0;
+/* Layered so Tailwind utilities (h-, p-, m-, gap-…) can override the reset.
+   An unlayered reset silently wins over every `@layer utilities` rule. */
+@layer base {
+  *,
+  *::before,
+  *::after {
+    box-sizing: border-box;
+    margin: 0;
+    padding: 0;
+  }
 }
 
 html,
diff --git a/app/workbench/src/ComposerContextParts.test.tsx b/app/workbench/src/ComposerContextParts.test.tsx
index c61dc984d..e8784cab7 100644
--- a/app/workbench/src/ComposerContextParts.test.tsx
+++ b/app/workbench/src/ComposerContextParts.test.tsx
@@ -2,7 +2,6 @@ import '@testing-library/jest-dom/vitest';
 import { fireEvent, render, screen } from '@testing-library/react';
 import { beforeAll, describe, expect, it, vi } from 'vitest';
 import {
-  ComposerMainchainStrip,
   ComposerMentionChips,
   ComposerQuoteBar,
   ComposerReplyBar,
@@ -59,20 +58,8 @@ describe('ComposerContextParts', () => {
     expect(onRemove).toHaveBeenCalledWith('profile-builder');
   });
 
-  it('renders mainchain and status strips', () => {
-    render(
-      <ComposerMainchainStrip
-        mainchainTask="draft required"
-        selectedAgentLabel="@Builder"
-        selectedTargetLabel={undefined}
-        targetSelected={false}
-      />,
-    );
-    expect(screen.getByText('Agent @Builder')).toBeInTheDocument();
-    expect(screen.getByText('目标未选')).toBeInTheDocument();
-    expect(screen.getByText('需填写内容')).toBeInTheDocument();
-
-    render(<ComposerStatusStrip statusItems={['数据：真实数据']} />);
-    expect(screen.getByText('数据：真实数据')).toBeInTheDocument();
+  it('renders the status strip as one quiet line', () => {
+    render(<ComposerStatusStrip statusItems={['数据：真实数据', '目标：就绪']} />);
+    expect(screen.getByRole('status')).toHaveTextContent('数据：真实数据 · 目标：就绪');
   });
 });
diff --git a/app/workbench/src/ComposerContextParts.tsx b/app/workbench/src/ComposerContextParts.tsx
index fe7e6e4fa..f9ca11cc2 100644
--- a/app/workbench/src/ComposerContextParts.tsx
+++ b/app/workbench/src/ComposerContextParts.tsx
@@ -9,12 +9,8 @@ import { Button } from '@shared/shadcn/ui/button';
 import { cn } from '@shared/lib/utils';
 import { DesignNavIcon } from './designIcons';
 import {
-  formatMainchainAgentLabel,
-  formatMainchainTargetLabel,
-  formatMainchainTaskLabel,
   formatMentionChipLabel,
   formatReplyToLabel,
-  mainchainDataState,
 } from './ComposerPartsHelpers';
 import { formatQuotePreview } from './unifiedComposerHelpers';
 
@@ -153,67 +149,18 @@ export function ComposerMentionChips({
   );
 }
 
-export function ComposerMainchainStrip({
-  selectedAgentLabel,
-  selectedTargetLabel,
-  targetSelected,
-  mainchainTask,
-}: {
-  selectedAgentLabel: string;
-  selectedTargetLabel: string | undefined;
-  targetSelected: boolean;
-  mainchainTask: 'ready' | 'draft required';
-}): React.ReactElement {
-  const { t } = useTranslation(CHATVIEW_I18N_NAMESPACE);
-  return (
-    <div
-      aria-label={t('aria.agentMainChain')}
-      className="flex flex-wrap items-center gap-1.5 text-[11px] text-muted-foreground"
-    >
-      <span
-        className="inline-flex items-center rounded-full border border-primary/20 bg-primary/10 px-2.5 py-1 font-medium text-foreground"
-        data-state="selected"
-      >
-        {formatMainchainAgentLabel(selectedAgentLabel, t)}
-      </span>
-      <span
-        className={cn(
-          'inline-flex items-center rounded-full border border-line bg-foreground/5 px-2.5 py-1',
-          mainchainDataState(targetSelected) === 'missing' && 'border-warning/40 bg-warning/10 text-warning',
-        )}
-        data-state={mainchainDataState(targetSelected)}
-      >
-        {formatMainchainTargetLabel(selectedTargetLabel, t)}
-      </span>
-      <span
-        className={cn(
-          'inline-flex items-center rounded-full border border-line bg-foreground/5 px-2.5 py-1',
-          mainchainDataState(mainchainTask === 'ready') === 'missing' && 'border-warning/40 bg-warning/10 text-warning',
-        )}
-        data-state={mainchainDataState(mainchainTask === 'ready')}
-      >
-        {formatMainchainTaskLabel(mainchainTask, t)}
-      </span>
-    </div>
-  );
-}
-
 export function ComposerStatusStrip({
   statusItems,
 }: {
   statusItems: string[];
 }): React.ReactElement {
   return (
-    <div
-      className="flex min-w-0 flex-wrap items-center gap-x-4 gap-y-1 px-1 text-[11px] leading-4 text-muted-foreground/80"
+    <p
+      className="w-full min-w-0 truncate px-1 text-[11px] leading-4 text-muted-foreground/60"
       role="status"
+      title={statusItems.join(' · ')}
     >
-      {statusItems.map((item) => (
-        <span className="inline-flex min-w-0 items-center gap-1.5" key={item}>
-          <span aria-hidden="true" className="size-1 shrink-0 rounded-full bg-current opacity-50" />
-          <span className="truncate">{item}</span>
-        </span>
-      ))}
-    </div>
+      {statusItems.join(' · ')}
+    </p>
   );
 }
diff --git a/app/workbench/src/ComposerControlParts.tsx b/app/workbench/src/ComposerControlParts.tsx
index e883acb35..9f99578a5 100644
--- a/app/workbench/src/ComposerControlParts.tsx
+++ b/app/workbench/src/ComposerControlParts.tsx
@@ -36,31 +36,28 @@ export function ComposerAgentPicker({
   onSelect: (agentId: string) => void;
 }): React.ReactElement {
   const { t } = useTranslation(CHATVIEW_I18N_NAMESPACE);
+  const placeholder = agentPickerPlaceholder(availableMentionOptions.length, t);
   return (
-    <label className="group/picker relative inline-flex h-8 min-w-0 items-center gap-1.5 rounded-full px-2.5 text-xs font-medium text-muted-foreground transition-colors hover:bg-muted hover:text-foreground focus-within:bg-muted focus-within:text-foreground has-[:disabled]:opacity-50">
-      <DesignNavIcon className="shrink-0" name="agent" size={14} />
-      <span className="sr-only">{t('composer.agentPicker')}</span>
+    <label className="group/picker relative inline-flex h-7 min-w-0 items-center gap-1.5 rounded-md px-2 text-xs text-muted-foreground transition-colors hover:bg-muted/60 hover:text-foreground focus-within:bg-muted/60 focus-within:text-foreground has-[:disabled]:opacity-40">
+      <DesignNavIcon className="shrink-0" name="agent" size={13} />
+      <span aria-hidden="true" className="max-w-[9.5rem] truncate">
+        {placeholder}
+      </span>
+      <DesignNavIcon className="shrink-0 opacity-50" name="chevron" size={10} />
       <select
         aria-label={t('aria.atAgent')}
-        className="h-8 min-w-0 max-w-[9.5rem] cursor-pointer appearance-none truncate bg-transparent pr-4 text-xs font-medium text-inherit outline-none disabled:cursor-not-allowed"
+        className="absolute inset-0 size-full cursor-pointer appearance-none opacity-0 disabled:cursor-not-allowed"
         disabled={isSubmitting || availableMentionOptions.length === 0}
         onChange={(event) => onSelect(event.target.value)}
         value=""
       >
-        <option value="">
-          {agentPickerPlaceholder(availableMentionOptions.length, t)}
-        </option>
+        <option value="">{placeholder}</option>
         {availableMentionOptions.map((agent) => (
           <option key={agent.id} value={agent.id}>
             {formatAgentOptionLabel(agent)}
           </option>
         ))}
       </select>
-      <DesignNavIcon
-        className="pointer-events-none absolute right-1.5 opacity-60"
-        name="chevron"
-        size={12}
-      />
     </label>
   );
 }
@@ -77,31 +74,31 @@ export function ComposerTargetPicker({
   onChange: (executionTargetId: string) => void;
 }): React.ReactElement {
   const { t } = useTranslation(CHATVIEW_I18N_NAMESPACE);
+  const selectedLabel = executionTargets.find(
+    (target) => target.id === executionTargetId,
+  )?.label;
+  const placeholder = selectedLabel ?? targetPickerPlaceholder(executionTargets.length, t);
   return (
-    <label className="group/picker relative inline-flex h-8 min-w-0 items-center gap-1.5 rounded-full px-2.5 text-xs font-medium text-muted-foreground transition-colors hover:bg-muted hover:text-foreground focus-within:bg-muted focus-within:text-foreground has-[:disabled]:opacity-50">
-      <DesignNavIcon className="shrink-0" name="laptop" size={14} />
-      <span className="sr-only">{t('composer.targetPicker')}</span>
+    <label className="group/picker relative inline-flex h-7 min-w-0 max-w-[14rem] items-center gap-1.5 rounded-md px-2 text-xs text-muted-foreground transition-colors hover:bg-muted/60 hover:text-foreground focus-within:bg-muted/60 focus-within:text-foreground has-[:disabled]:opacity-40">
+      <DesignNavIcon className="shrink-0" name="laptop" size={13} />
+      <span aria-hidden="true" className="truncate">
+        {placeholder}
+      </span>
+      <DesignNavIcon className="shrink-0 opacity-50" name="chevron" size={10} />
       <select
         aria-label={t('aria.target')}
-        className="h-8 min-w-0 max-w-[11rem] cursor-pointer appearance-none truncate bg-transparent pr-4 text-xs font-medium text-inherit outline-none disabled:cursor-not-allowed"
+        className="absolute inset-0 size-full cursor-pointer appearance-none opacity-0 disabled:cursor-not-allowed"
         disabled={isSubmitting || executionTargets.length === 0}
         onChange={(event) => onChange(event.target.value)}
         value={executionTargetId}
       >
-        <option value="">
-          {targetPickerPlaceholder(executionTargets.length, t)}
-        </option>
+        <option value="">{targetPickerPlaceholder(executionTargets.length, t)}</option>
         {executionTargets.map((target) => (
           <option key={target.id} value={target.id}>
             {target.label}
           </option>
         ))}
       </select>
-      <DesignNavIcon
-        className="pointer-events-none absolute right-1.5 opacity-60"
-        name="chevron"
-        size={12}
-      />
     </label>
   );
 }
@@ -127,7 +124,7 @@ export function ComposerSendButton({
     return (
       <Button
         aria-label={t('action.stopRun')}
-        className="size-9 shrink-0 rounded-full shadow-sm"
+        className="size-8 shrink-0 rounded-full"
         data-running="true"
         size="icon-lg"
         type="button"
@@ -141,7 +138,7 @@ export function ComposerSendButton({
   return (
     <Button
       aria-label={hasMentions ? t('action.startAgentTask') : t('profile.sendMessage')}
-      className="size-9 shrink-0 rounded-full shadow-sm"
+      className="size-8 shrink-0 rounded-full"
       disabled={submitDisabled}
       size="icon-lg"
       type="submit"
@@ -162,7 +159,7 @@ export function ComposerAttachButton({
   return (
     <Button
       aria-label={t('aria.addAttachment')}
-      className="size-8 shrink-0 rounded-full text-muted-foreground"
+      className="size-7 shrink-0 rounded-md text-muted-foreground"
       disabled={isSubmitting}
       size="icon-sm"
       onClick={onClick}
@@ -207,7 +204,7 @@ export function ComposerApprovalModePicker({
       options={options}
       disabled={isSubmitting}
       className="shrink-0"
-      triggerClassName="max-w-[11rem] rounded-full bg-transparent! text-xs! font-medium! text-muted-foreground! hover:bg-muted! hover:text-foreground! aria-expanded:bg-muted! aria-expanded:text-foreground!"
+      triggerClassName="max-w-[11rem] rounded-md bg-transparent! text-xs! text-muted-foreground! hover:bg-muted/60! hover:text-foreground! aria-expanded:bg-muted/60! aria-expanded:text-foreground!"
       onChange={(value) => {
         const mode = pickerValueToApprovalMode(value);
         if (mode) onChange(mode);
diff --git a/app/workbench/src/ComposerPartsHelpers.test.ts b/app/workbench/src/ComposerPartsHelpers.test.ts
index 8535118c6..33ef9ebe7 100644
--- a/app/workbench/src/ComposerPartsHelpers.test.ts
+++ b/app/workbench/src/ComposerPartsHelpers.test.ts
@@ -4,13 +4,9 @@ import {
   agentPickerPlaceholder,
   buildAttachmentChipViewModel,
   formatAgentOptionLabel,
-  formatMainchainAgentLabel,
-  formatMainchainTargetLabel,
-  formatMainchainTaskLabel,
   formatMentionChipLabel,
   formatReplyToLabel,
   isMediaAttachment,
-  mainchainDataState,
   resolveAttachmentPreviewKind,
   resolveAttachmentUploadProgress,
   targetPickerPlaceholder,
@@ -32,18 +28,11 @@ const textAttachment: ComposerAttachment = {
 };
 
 describe('ComposerPartsHelpers', () => {
-  it('formats reply, mention, and mainchain labels without UX drift', () => {
+  it('formats reply and mention labels without UX drift', () => {
     expect(formatReplyToLabel({ author: 'Ada', preview: 'hello' })).toBe(
       '回复至 Ada: hello',
     );
     expect(formatMentionChipLabel({ id: 'a1', label: 'Builder' })).toBe('@Builder');
-    expect(formatMainchainAgentLabel('@Builder')).toBe('Agent @Builder');
-    expect(formatMainchainTargetLabel(undefined)).toBe('目标未选');
-    expect(formatMainchainTargetLabel('Desktop')).toBe('目标 Desktop');
-    expect(formatMainchainTaskLabel('ready')).toBe('任务就绪');
-    expect(formatMainchainTaskLabel('draft required')).toBe('需填写内容');
-    expect(mainchainDataState(true)).toBe('selected');
-    expect(mainchainDataState(false)).toBe('missing');
   });
 
   it('builds picker placeholders and agent option labels', () => {
diff --git a/app/workbench/src/ComposerPartsHelpers.ts b/app/workbench/src/ComposerPartsHelpers.ts
index 8d31705cf..926d1dd82 100644
--- a/app/workbench/src/ComposerPartsHelpers.ts
+++ b/app/workbench/src/ComposerPartsHelpers.ts
@@ -31,38 +31,6 @@ export function formatMentionChipLabel(mention: ComposerMention): string {
   return `@${mention.label}`;
 }
 
-export function formatMainchainAgentLabel(selectedAgentLabel: string, t?: TFunction): string {
-  const label = selectedAgentLabel.trim();
-  if (!label) return t?.('composer.mainchain.agentUnselected') ?? 'Agent 未选';
-  return label.startsWith('@')
-    ? (t?.('composer.mainchain.agentPlain', { label }) ?? `Agent ${label}`)
-    : (t?.('composer.mainchain.agentAt', { label }) ?? `Agent @${label}`);
-}
-
-export function formatMainchainTargetLabel(
-  selectedTargetLabel: string | undefined,
-  t?: TFunction,
-): string {
-  return selectedTargetLabel
-    ? (t?.('composer.mainchain.targetSelected', { label: selectedTargetLabel }) ?? `目标 ${selectedTargetLabel}`)
-    : (t?.('composer.mainchain.targetUnselected') ?? '目标未选');
-}
-
-export function formatMainchainTaskLabel(
-  mainchainTask: 'ready' | 'draft required',
-  t?: TFunction,
-): string {
-  return mainchainTask === 'ready'
-    ? (t?.('composer.mainchain.taskReady') ?? '任务就绪')
-    : (t?.('composer.mainchain.taskDraftRequired') ?? '需填写内容');
-}
-
-export function mainchainDataState(
-  selected: boolean,
-): 'selected' | 'missing' {
-  return selected ? 'selected' : 'missing';
-}
-
 export function agentPickerPlaceholder(
   availableCount: number,
   t?: TFunction,
diff --git a/app/workbench/src/UnifiedComposer.tsx b/app/workbench/src/UnifiedComposer.tsx
index 7532f316a..d85c208fc 100644
--- a/app/workbench/src/UnifiedComposer.tsx
+++ b/app/workbench/src/UnifiedComposer.tsx
@@ -34,7 +34,6 @@ import {
   ComposerAttachButton as ComposerAttachButtonBase,
   ComposerAttachmentBar as ComposerAttachmentBarBase,
   ComposerEditBar as ComposerEditBarBase,
-  ComposerMainchainStrip as ComposerMainchainStripBase,
   ComposerMentionChips as ComposerMentionChipsBase,
   ComposerQuoteBar as ComposerQuoteBarBase,
   ComposerReplyBar as ComposerReplyBarBase,
@@ -53,7 +52,6 @@ const ComposerReplyBar = React.memo(ComposerReplyBarBase);
 const ComposerQuoteBar = React.memo(ComposerQuoteBarBase);
 const ComposerEditBar = React.memo(ComposerEditBarBase);
 const ComposerMentionChips = React.memo(ComposerMentionChipsBase);
-const ComposerMainchainStrip = React.memo(ComposerMainchainStripBase);
 const ComposerAttachmentBar = React.memo(ComposerAttachmentBarBase);
 const ComposerTargetPicker = React.memo(ComposerTargetPickerBase);
 const ComposerSendButton = React.memo(ComposerSendButtonBase);
@@ -636,7 +634,7 @@ export function UnifiedComposer({
       onDragLeave={handleFormDragLeave}
       onDrop={handleFormDrop}
     >
-      <div className="pointer-events-auto mx-auto flex w-full max-w-3xl flex-col gap-2">
+      <div className="pointer-events-auto mx-auto flex w-full min-w-0 max-w-3xl flex-col gap-2">
       <InputGroup
         className={cn(
           'relative flex-col items-stretch rounded-2xl border-line bg-card shadow-[0_1px_2px_rgb(0_0_0/0.04),0_12px_32px_-20px_rgb(0_0_0/0.22)] transition-[border-color,box-shadow]',
@@ -655,12 +653,11 @@ export function UnifiedComposer({
           || chromeModel.quote
           || composer.editingMessageId
           || chromeModel.mentions
-          || chromeModel.mainchain
           || chromeModel.attachment
           || (view.isSubmitting && inFlightUploadSummaries.length > 0)) && (
           <InputGroupAddon
             align="block-start"
-            className="w-full cursor-default select-auto flex-col items-stretch gap-2 border-b border-line/60 px-3 pb-2.5 pt-2.5"
+            className="w-full cursor-default select-auto flex-col items-stretch gap-1.5 px-3 pb-1 pt-2.5"
           >
             {chromeModel.replyTo && (
               <ComposerReplyBar
@@ -689,14 +686,6 @@ export function UnifiedComposer({
                 onRemove={handleRemoveMention}
               />
             )}
-            {chromeModel.mainchain && (
-              <ComposerMainchainStrip
-                mainchainTask={chromeModel.mainchain.mainchainTask}
-                selectedAgentLabel={chromeModel.mainchain.selectedAgentLabel}
-                selectedTargetLabel={chromeModel.mainchain.selectedTargetLabel}
-                targetSelected={chromeModel.mainchain.targetSelected}
-              />
-            )}
             {chromeModel.attachment && (
               <ComposerAttachmentBar
                 attachments={chromeModel.attachment.attachments}
@@ -734,7 +723,7 @@ export function UnifiedComposer({
               : undefined
           }
           data-composer-input
-          className="max-h-44 min-h-[54px] resize-none rounded-none border-0 bg-transparent px-4 pt-3.5 pb-1.5 text-[0.9375rem] leading-6 text-foreground shadow-none placeholder:text-muted-foreground/70 focus-visible:ring-0"
+          className="max-h-44 min-h-[44px] resize-none rounded-none border-0 bg-transparent px-4 pt-3 pb-1 text-[0.9375rem] leading-6 text-foreground shadow-none placeholder:text-muted-foreground/70 focus-visible:ring-0"
           ref={setTextareaRef}
           onChange={handleTextChange}
           onCompositionStart={() => {
@@ -763,10 +752,9 @@ export function UnifiedComposer({
         />
         <InputGroupAddon
           align="block-end"
-          className="flex-wrap items-center gap-0.5 border-t border-line/70 px-2 py-1.5"
+          className="flex-wrap items-center gap-0.5 px-2 pb-2 pt-0"
         >
           <ComposerAttachButton isSubmitting={view.isSubmitting} onClick={openFilePicker} />
-          <span aria-hidden="true" className="mx-0.5 h-4 w-px bg-line" />
           {chromeModel.agentOptions && (
             <ComposerAgentPicker
               availableMentionOptions={chromeModel.agentOptions}
@@ -787,10 +775,7 @@ export function UnifiedComposer({
             isSubmitting={view.isSubmitting}
             onChange={(mode) => dispatchComposer({ type: 'setApprovalMode', approvalMode: mode })}
           />
-          <div className="ml-auto flex items-center gap-2 pl-1">
-            <kbd className="hidden rounded border border-line bg-muted/60 px-1.5 py-0.5 font-mono text-[10px] text-muted-foreground sm:inline-block">
-              Enter
-            </kbd>
+          <div className="ml-auto flex items-center pl-1">
             <ComposerSendButton
               hasMentions={view.hasMentions}
               isRunning={isRunning}
diff --git a/app/workbench/src/UnifiedComposerParts.tsx b/app/workbench/src/UnifiedComposerParts.tsx
index 816ad81be..e441b0bf0 100644
--- a/app/workbench/src/UnifiedComposerParts.tsx
+++ b/app/workbench/src/UnifiedComposerParts.tsx
@@ -7,7 +7,6 @@
    ═══════════════════════════════════════════════════════════════════════ */
 
 export {
-  ComposerMainchainStrip,
   ComposerMentionChips,
   ComposerQuoteBar,
   ComposerReplyBar,
diff --git a/app/workbench/src/__tests__/composer.test.tsx b/app/workbench/src/__tests__/composer.test.tsx
index 9f02a0bed..6286c7b03 100644
--- a/app/workbench/src/__tests__/composer.test.tsx
+++ b/app/workbench/src/__tests__/composer.test.tsx
@@ -171,13 +171,13 @@ describe('AgentHubWorkbench', () => {
     fireEvent.change(screen.getByLabelText('执行目标'), {
       target: { value: 'target-local-edge-1' },
     });
-    expect(screen.getByText('Agent @Builder')).toBeInTheDocument();
-    expect(screen.getByText('目标 Alpha Desktop')).toBeInTheDocument();
-    expect(screen.getByText('需填写内容')).toBeInTheDocument();
+    expect(screen.getByText('@Builder')).toBeInTheDocument();
+    expect(screen.getByLabelText('执行目标')).toHaveValue('target-local-edge-1');
+    expect(screen.getByRole('button', { name: '启动 Agent 任务' })).toBeDisabled();
     fireEvent.change(screen.getByRole('textbox', { name: '输入框' }), {
       target: { value: 'Start the Web main chain' },
     });
-    expect(screen.getByText('任务就绪')).toBeInTheDocument();
+    expect(screen.getByRole('button', { name: '启动 Agent 任务' })).toBeEnabled();
     fireEvent.click(screen.getByRole('button', { name: '启动 Agent 任务' }));
 
     await waitFor(() => {
@@ -291,9 +291,7 @@ describe('AgentHubWorkbench', () => {
       target: { value: 'Run the remote task' },
     });
 
-    expect(screen.getByText('Agent @Builder')).toBeInTheDocument();
-    expect(screen.getByText('目标未选')).toBeInTheDocument();
-    expect(screen.getByText('需填写内容')).toBeInTheDocument();
+    expect(screen.getByLabelText('执行目标')).toHaveValue('');
     expect(screen.getAllByRole('status').find((el) => el.textContent?.includes('请先选择执行目标'))).toHaveTextContent('请先选择执行目标再开始。');
     expect(screen.getByRole('button', { name: '启动 Agent 任务' })).toBeDisabled();
     expect(platform.submittedIntents).toEqual([]);
diff --git a/app/workbench/src/unifiedComposerHelpers.test.ts b/app/workbench/src/unifiedComposerHelpers.test.ts
index ea0facee9..997bec396 100644
--- a/app/workbench/src/unifiedComposerHelpers.test.ts
+++ b/app/workbench/src/unifiedComposerHelpers.test.ts
@@ -12,14 +12,12 @@ import {
   formatComposerDataModeLabel,
   formatComposerTargetStateLabel,
   formatQuotePreview,
-  formatSelectedAgentLabel,
   isAttachmentUploadFailed,
   isAttachmentUploadInFlight,
   isAttachmentUploading,
   isExecutionTargetStillValid,
   isImageAttachment,
   isTargetSelectionRequired,
-  mainchainTaskState,
   partitionAttachmentsBySize,
   resolveTargetStatus,
   shouldSubmitComposerKey,
@@ -145,12 +143,10 @@ describe('unifiedComposerHelpers', () => {
     })).toBe(true);
   });
 
-  it('derives composer chrome labels and task readiness', () => {
-    expect(formatSelectedAgentLabel(baseComposer.mentions)).toBe('@Builder');
+  it('derives composer status and target validity', () => {
     expect(formatQuotePreview({ author: 'Ada', text: 'x'.repeat(80) })).toBe(
       `Ada: ${'x'.repeat(60)}`,
     );
-    expect(mainchainTaskState({ composer: baseComposer, targetSelected: true })).toBe('ready');
     expect(isExecutionTargetStillValid([{ id: 't1', label: 'A' }], 't2')).toBe(false);
     expect(isImageAttachment({
       id: 'a1',
@@ -177,11 +173,9 @@ describe('unifiedComposerHelpers', () => {
     expect(derived.targetSelectionRequired).toBe(true);
     expect(derived.targetSelected).toBe(false);
     expect(derived.submitDisabled).toBe(true);
-    expect(derived.selectedAgentLabel).toBe('@Builder');
     expect(derived.availableMentionOptions).toHaveLength(1);
     expect(derived.statusItems).toContain('数据：真实数据');
     expect(derived.statusItems).toContain('请先选择执行目标再开始。');
-    expect(derived.mainchainTask).toBe('draft required');
   });
 
   describe('attachment size limit', () => {
diff --git a/app/workbench/src/unifiedComposerHelpers.ts b/app/workbench/src/unifiedComposerHelpers.ts
index 81a9090f8..1ea2ba108 100644
--- a/app/workbench/src/unifiedComposerHelpers.ts
+++ b/app/workbench/src/unifiedComposerHelpers.ts
@@ -93,17 +93,6 @@ function isExecutionTargetSelected(
   return !targetSelectionRequired || executionTargetId.trim().length > 0;
 }
 
-function resolveSelectedTargetLabel(
-  executionTargets: ComposerExecutionTarget[] | undefined,
-  executionTargetId: string,
-): string | undefined {
-  return executionTargets?.find((target) => target.id === executionTargetId)?.label;
-}
-
-export function formatSelectedAgentLabel(mentions: ComposerMention[]): string {
-  return mentions.map((mention) => `@${mention.label}`).join(', ');
-}
-
 export function resolveTargetStatus(params: {
   targetSelectionRequired: boolean;
   executionTargetId: string;
@@ -187,14 +176,6 @@ function isComposerSubmitDisabled(params: {
   return !canSubmitComposer(composer) || isSubmitting || !targetSelected;
 }
 
-export function mainchainTaskState(params: {
-  composer: ComposerState;
-  targetSelected: boolean;
-}): 'ready' | 'draft required' {
-  const { composer, targetSelected } = params;
-  return canSubmitComposer(composer) && targetSelected ? 'ready' : 'draft required';
-}
-
 export function isExecutionTargetStillValid(
   executionTargets: ComposerExecutionTarget[] | undefined,
   executionTargetId: string,
@@ -298,12 +279,9 @@ export interface UnifiedComposerDerivedState {
   targetSelectionRequired: boolean;
   targetSelected: boolean;
   submitDisabled: boolean;
-  selectedTargetLabel: string | undefined;
-  selectedAgentLabel: string;
   targetStatus: string | undefined;
   availableMentionOptions: ComposerMention[];
   statusItems: string[];
-  mainchainTask: 'ready' | 'draft required';
 }
 
 export function deriveUnifiedComposerState(params: {
@@ -339,11 +317,8 @@ export function deriveUnifiedComposerState(params: {
       isSubmitting,
       targetSelected,
     }),
-    selectedTargetLabel: resolveSelectedTargetLabel(executionTargets, executionTargetId),
-    selectedAgentLabel: formatSelectedAgentLabel(composer.mentions),
     targetStatus,
     availableMentionOptions: filterAvailableMentionOptions(mentionableAgents, composer.mentions),
     statusItems: buildComposerStatusItems({ status, targetStatus }),
-    mainchainTask: mainchainTaskState({ composer, targetSelected }),
   };
 }
diff --git a/app/workbench/src/unifiedComposerHostHelpers.test.ts b/app/workbench/src/unifiedComposerHostHelpers.test.ts
index 2f51fefef..4a381a162 100644
--- a/app/workbench/src/unifiedComposerHostHelpers.test.ts
+++ b/app/workbench/src/unifiedComposerHostHelpers.test.ts
@@ -92,7 +92,6 @@ describe('unifiedComposerHostHelpers', () => {
       replyBar: false,
       quoteBar: false,
       mentionChips: false,
-      mainchainStrip: false,
       attachmentBar: false,
       agentPicker: false,
       targetPicker: false,
@@ -146,7 +145,6 @@ describe('unifiedComposerHostHelpers', () => {
     expect(model.replyTo?.author).toBe('Ada');
     expect(model.quote?.text).toBe('quoted');
     expect(model.mentions).toHaveLength(1);
-    expect(model.mainchain?.mainchainTask).toBe('ready');
     expect(model.attachment?.uploadProgresses?.a1?.percent).toBe(10);
     expect(model.agentOptions).toHaveLength(1);
     expect(model.targetPicker?.executionTargetId).toBe('t1');
@@ -171,11 +169,9 @@ describe('unifiedComposerHostHelpers', () => {
     expect(vm.targetSelectionRequired).toBe(true);
     expect(vm.targetSelected).toBe(false);
     expect(vm.submitDisabled).toBe(true);
-    expect(vm.selectedAgentLabel).toBe('@Builder');
     expect(vm.availableMentionOptions).toHaveLength(1);
     expect(vm.statusItems).toContain('数据：真实数据');
     expect(vm.statusItems).toContain('请先选择执行目标再开始。');
-    expect(vm.mainchainTask).toBe('draft required');
     expect(vm.hasMentions).toBe(true);
     expect(vm.inputPlaceholder).toBe('发消息给 AgentHub');
     expect(vm.fileAccept).toBe('image/*');
diff --git a/app/workbench/src/unifiedComposerHostHelpers.ts b/app/workbench/src/unifiedComposerHostHelpers.ts
index f2ef40c14..bbfe9386a 100644
--- a/app/workbench/src/unifiedComposerHostHelpers.ts
+++ b/app/workbench/src/unifiedComposerHostHelpers.ts
@@ -19,7 +19,6 @@ export type {
   UnifiedComposerProps,
   ComposerChromeVisibility,
   ComposerHostRuntimeDefaults,
-  ComposerHostMainchainModel,
   ComposerHostAttachmentModel,
   ComposerHostTargetPickerModel,
   ComposerHostChromeModel,
diff --git a/app/workbench/src/unifiedComposerHostViewModel.test.ts b/app/workbench/src/unifiedComposerHostViewModel.test.ts
index 8f8b1b17c..dc0ef3d2f 100644
--- a/app/workbench/src/unifiedComposerHostViewModel.test.ts
+++ b/app/workbench/src/unifiedComposerHostViewModel.test.ts
@@ -76,7 +76,6 @@ describe('unifiedComposerHostViewModel', () => {
       replyBar: false,
       quoteBar: false,
       mentionChips: false,
-      mainchainStrip: false,
       attachmentBar: false,
       agentPicker: false,
       targetPicker: false,
@@ -130,7 +129,6 @@ describe('unifiedComposerHostViewModel', () => {
     expect(model.replyTo?.author).toBe('Ada');
     expect(model.quote?.text).toBe('quoted');
     expect(model.mentions).toHaveLength(1);
-    expect(model.mainchain?.mainchainTask).toBe('ready');
     expect(model.attachment?.uploadProgresses?.a1?.percent).toBe(10);
     expect(model.agentOptions).toHaveLength(1);
     expect(model.targetPicker?.executionTargetId).toBe('t1');
@@ -155,7 +153,6 @@ describe('unifiedComposerHostViewModel', () => {
     expect(vm.targetSelectionRequired).toBe(true);
     expect(vm.targetSelected).toBe(false);
     expect(vm.submitDisabled).toBe(true);
-    expect(vm.selectedAgentLabel).toBe('@Builder');
     expect(vm.availableMentionOptions).toHaveLength(1);
     expect(vm.hasMentions).toBe(true);
     expect(vm.inputPlaceholder).toBe('发消息给 AgentHub');
diff --git a/app/workbench/src/unifiedComposerHostViewModel.ts b/app/workbench/src/unifiedComposerHostViewModel.ts
index 71bcbeb82..428925af5 100644
--- a/app/workbench/src/unifiedComposerHostViewModel.ts
+++ b/app/workbench/src/unifiedComposerHostViewModel.ts
@@ -77,7 +77,6 @@ export interface ComposerChromeVisibility {
   replyBar: boolean;
   quoteBar: boolean;
   mentionChips: boolean;
-  mainchainStrip: boolean;
   attachmentBar: boolean;
   agentPicker: boolean;
   targetPicker: boolean;
@@ -92,13 +91,6 @@ export interface ComposerHostRuntimeDefaults {
   hasNativePicker: boolean;
 }
 
-export interface ComposerHostMainchainModel {
-  mainchainTask: 'ready' | 'draft required';
-  selectedAgentLabel: string;
-  selectedTargetLabel: string | undefined;
-  targetSelected: boolean;
-}
-
 export interface ComposerHostAttachmentModel {
   attachments: ComposerAttachment[];
   uploadProgresses: Record<string, AttachmentUploadState> | undefined;
@@ -113,7 +105,6 @@ export interface ComposerHostChromeModel {
   replyTo: ReplyToContext | null;
   quote: QuoteContext | null;
   mentions: ComposerMention[] | null;
-  mainchain: ComposerHostMainchainModel | null;
   attachment: ComposerHostAttachmentModel | null;
   agentOptions: ComposerMention[] | null;
   targetPicker: ComposerHostTargetPickerModel | null;
@@ -185,8 +176,6 @@ export function deriveComposerChromeVisibility(params: {
     replyBar: Boolean(composer.replyTo),
     quoteBar: Boolean(composer.quote),
     mentionChips: hasMentions,
-    /* Show mainchain when mentions or targets exist so Agent/目标/任务 always readable. */
-    mainchainStrip: hasMentions || hasExecutionTargets,
     attachmentBar: composer.attachments.length > 0,
     agentPicker: mentionableAgentsCount > 0,
     targetPicker: hasExecutionTargets,
@@ -219,14 +208,6 @@ export function buildComposerHostChromeModel(params: {
     replyTo: chrome.replyBar && composer.replyTo ? composer.replyTo : null,
     quote: chrome.quoteBar && composer.quote ? composer.quote : null,
     mentions: chrome.mentionChips ? composer.mentions : null,
-    mainchain: chrome.mainchainStrip
-      ? {
-          mainchainTask: derived.mainchainTask,
-          selectedAgentLabel: derived.selectedAgentLabel,
-          selectedTargetLabel: derived.selectedTargetLabel,
-          targetSelected: derived.targetSelected,
-        }
-      : null,
     attachment: chrome.attachmentBar
       ? {
           attachments: composer.attachments,
diff --git a/docs/architecture/07-design-system-ssot.md b/docs/architecture/07-design-system-ssot.md
index 0f2ae00ed..fce02a88b 100644
--- a/docs/architecture/07-design-system-ssot.md
+++ b/docs/architecture/07-design-system-ssot.md
@@ -39,7 +39,7 @@ Entry CSS load: desktop/web `main.tsx` imports surface `styles/{tokens,themes,pr
 8. **Design token gate**：修改 `app/shared/src/styles/` 或 `app/shared/src/designTokens.ts` 后，运行 `pnpm --dir app --filter @agenthub/shared test`；`designTokens.test.ts`、`styles/tokens-base.test.ts`、`styles/surfaceStyles.test.ts` 必须全绿。
 9. **Shared component acceptance**：新组件验收见 [component-acceptance.md](../component-acceptance.md)。
 10. **New chat surfaces** use the vendored shadcn primitives (`Message`, `Bubble`, `InputGroup`, `Attachment`) plus Tailwind utilities whose colors/radii resolve from `shadcn.css`. Do not add a second palette or a component-local radius scale.
-11. **Preflight stays off during migration.** `shadcn.css` imports Tailwind theme + utilities only; enabling Preflight would reset legacy CSS-Module surfaces. Remove this exception only in the change that retires the last migrated module.
+11. **Preflight stays off during migration.** `shadcn.css` imports Tailwind theme + utilities only; enabling Preflight would reset legacy CSS-Module surfaces. Remove this exception only in the change that retires the last migrated module. The hand-rolled reset in `tokens-base.css` therefore lives inside `@layer base`: an unlayered `*, *::before, *::after { margin: 0; padding: 0 }` wins over every `@layer utilities` rule and silently kills `m-*`, `mx-auto` and `space-*`.
 12. **Flat chrome, glass overlays.** Workbench chrome (rail, sidebar, header, inspector, composer) uses flat `--background` / `--surface-dim` surfaces and 9–18% foreground hairlines. Frosted glass remains for transient overlays and previews, not for the persistent shell.
 
 ## 3. Legitimate surface glue (not forks)