feat(web): replace the plan select with a status chip and placeholder swap

Plan mode is entered through /plan only — the select control is retired.
The conversation.input.plan seat (now right of the access-mode control)
renders a read-only Plan chip while the projection's effective target is
plan mode; its hover x executes /plan off, and the chip follows the folded
target (appears on /plan immediately, disappears on /plan off) with frames
correcting either way. While plan mode is targeted the composer textarea's
placeholder switches to the plan-task wording — InputBar reads the same
projection through the standard-kit useProjection (the TodoDock posture:
a type-only key merge, no domain service edge), and owner placeholders
still win.

packages/client/ui-conversation/src/client/apply.ts

@@ -129,8 +129,9 @@ export function apply(ctx: Context): void {
   // verbs ride this inject (package-internal — hub and bar are one plugin).
   slots.register({
     name: 'conversation.composer.bar',
-    // The two named control seats in the bar's tool row (plan left, model
-    // right); empty until their owning plugins register (B ruling).
+    // The two named control seats in the bar's tool row (plan beside the
+    // access control, model right); empty until their owning plugins
+    // register (B ruling).
     children: {
       'conversation.input.plan': { kind: 'single', scope: 'session' },
       'conversation.input.model': { kind: 'single', scope: 'session' },

packages/client/ui-conversation/src/client/contract/slots.ts

@@ -83,9 +83,10 @@ declare module '@deepseek-ai/dsh-client-ui-slots' {
      */
     'conversation.composer.bar': { kind: 'single'; scope: 'session'; owner: ComposerBarOwnerProps }
     /**
-     * The Plan-mode control seat in the composer tool row (left group).
-     * Declared by the composer-bar entry; empty until a plan plugin
-     * registers (B ruling: no placeholder fallback).
+     * The Plan-mode status seat in the composer tool row (left group,
+     * right of the access-mode control). Declared by the composer-bar
+     * entry; empty until a plan plugin registers (B ruling: no placeholder
+     * fallback).
      */
     'conversation.input.plan': { kind: 'single'; scope: 'session'; owner: InputControlOwnerProps }
     /**

packages/client/ui-conversation/src/client/skeleton/InputBar.tsx

@@ -10,6 +10,9 @@ import { useEffect, useRef, useState } from 'react'
 import type { ChangeEvent, KeyboardEvent, MouseEvent, ReactNode } from 'react'
 import clsx from 'clsx'
 import { IconPlusOutline16 } from '@deepseek-ai/dsh-client-ui-primitives'
+// Type-only: the `plan` projection key merge (the TodoDock posture — the
+// composer reads a host-computed value; the domain owns the key).
+import type {} from '@deepseek-ai/dsh-plan-mode/client'
 import type { ComposerBarProps } from '../contract/slots.ts'
 import { deriveDecorations } from '../input/decorations.ts'
 import css from './InputBar.module.css'
@@ -28,7 +31,7 @@ const READONLY_OPTIONS: readonly { id: string; label: string }[] = [
 ]
 
 export function InputBar({
-  useSession, useInput, inputActions, keyboard, stop, renderSlot, useNotices, useLexicon,
+  useSession, useInput, inputActions, keyboard, stop, renderSlot, useNotices, useLexicon, useProjection,
   variant, placeholder, accessory, overlay, leftItems, rightItems, onAdd, addLabel = 'Add attachment',
 }: InputBarProps) {
   const input = useInput(s => s)
@@ -37,6 +40,9 @@ export function InputBar({
   const promptError = useSession(s => s.promptError)
   const running = useSession(s => s.running)
   const disabled = useSession(s => s.removed)
+  // Plan mode swaps the textarea placeholder (the projection is the folded
+  // host value; owner-prop placeholders — hero, session-unavailable — win).
+  const planActive = useProjection('plan', plan => plan !== undefined && (plan.pending ? !plan.active : plan.active))
   // Prompt failures are ordinary failures (no create/attach transaction
   // exists anymore): the strip renders promptError, the draft stays in the
   // machine, and the user resubmits.
@@ -334,7 +340,9 @@ export function InputBar({
             disabled={locked}
             readOnly={machineBusy}
             data-phase={input.phase}
-            placeholder={placeholder ?? (disabled ? 'Session unavailable' : 'Message the agent')}
+            placeholder={placeholder ?? (disabled
+              ? 'Session unavailable'
+              : planActive ? 'describe your task to generate plan' : 'Message the agent')}
             rows={2}
             onChange={onChange}
             onKeyDown={onKeyDown}
@@ -361,8 +369,8 @@ export function InputBar({
               <IconPlusOutline16 size={14} />
             </button>
             <div className={css.modes}>
-              {renderSlot('conversation.input.plan', { locked })}
               {accessSelect}
+              {renderSlot('conversation.input.plan', { locked })}
             </div>
             {leftItems}
           </div>