cleanup(web): remove the steering interjection caption

Steering bubbles render as plain user bubbles; a mid-turn steer is
recognizable by its position in the flow. The runtime SteeringMessageNode
projection and pending-steering lifecycle are unchanged.

Partially supersedes the 2026-08-04 context-source and steer marks note;
the new simplification note owns the removal rationale.

packages/client/ui-conversation/src/client/chat/MessageItem.module.css

@@ -8,15 +8,6 @@
   gap: 6px;
 }
 
-/* Steering caption above the bubble: mid-turn interjections carry the same
-   bubble as a turn-opening prompt, so the transcript names which one this is. */
-.steeringMark {
-  padding-right: 4px;
-  color: var(--dsw-alias-label-tertiary);
-  font-size: 12px;
-  line-height: 16px;
-}
-
 .bubble {
   /* 525px cap inside the 736 column; percentage keeps narrow windows sane. */
   max-width: min(525px, 82%);

packages/client/ui-conversation/src/client/chat/MessageItem.tsx

@@ -1,7 +1,6 @@
 // MessageItem: simple chat nodes — user and consumed-steering bubbles
-// (right-aligned, with clock + copy IconActions; steering adds the
-// interjection caption that names it; branch lives only under assistant
-// answers), pending steering (caption + copy only), context injection,
+// (right-aligned, with clock + copy IconActions; branch lives only under
+// assistant answers), pending steering (copy only), context injection,
 // compaction marker, retry disclosure, and unknown-surface JSON rows.
 
 import { memo, useEffect, useMemo, useState } from 'react'
@@ -151,22 +150,19 @@ function projectUserText(text: string): ReactNode {
 
 /** Right-aligned bubble shared by user and steering rows. */
 function UserStyleBubble({
-  content, actions, pending = false, steering = false, t,
+  content, actions, pending = false, t,
 }: {
   content: readonly unknown[]
   /** Optional IconActions (or similar) below the bubble; receives the joined text. */
   actions?: (text: string) => ReactNode
   /** Whether this is the Host-authoritative pre-admission steering projection. */
   pending?: boolean
-  /** Marks the bubble as mid-turn steering rather than a turn-opening prompt. */
-  steering?: boolean
   t: ChatViewSlotProps['t']
 }): ReactNode {
   const { text, rest } = contentText(content)
   const truncated = (total: number): string => t('json.truncated', { total })
   return (
     <div className={css.userRow} data-pending-steering={pending || undefined} data-time-hover-root>
-      {steering && <span className={css.steeringMark} data-steering-mark>{t('message.steering')}</span>}
       <div className={css.bubble}>
         {projectUserText(text)}
         {rest.map((block, i) => <JsonBlock key={i} label={t('message.extraBlock')} payload={block} truncatedLabel={truncated} />)}
@@ -190,7 +186,6 @@ export function PendingSteeringBubble({ content, t }: {
     <UserStyleBubble
       content={content}
       pending
-      steering
       t={t}
       actions={text => (
         <MessageIconActions
@@ -212,7 +207,6 @@ export const UserMessageNodeView = memo(function UserMessageNodeView({
   return (
     <UserStyleBubble
       content={data.content}
-      steering={data.kind === 'steering'}
       t={t}
       actions={text => (
         <MessageIconActions

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

@@ -79,7 +79,6 @@ export const zh = {
   'message.context.relay.from': '来自会话 {session}',
   'message.context.recall.counts': '保留 {retained} 条 · 省略 {omitted} 条',
   'message.context.recall.truncated': '已截断',
-  'message.steering': '插话',
   'message.compaction': '上下文已压缩',
   'message.compaction.running': '正在压缩…',
   'message.compaction.completed': '已压缩 {items} 条历史记录（约 {tokens} tokens）',
@@ -222,7 +221,6 @@ export const en = {
   'message.context.relay.from': 'From session {session}',
   'message.context.recall.counts': '{retained} kept · {omitted} omitted',
   'message.context.recall.truncated': 'truncated',
-  'message.steering': 'Interjection',
   'message.compaction': 'Context compacted',
   'message.compaction.running': 'Compacting context…',
   'message.compaction.completed': 'Compacted {items} history items (~{tokens} tokens)',