feat: render thinking process UI for intermediate agent messages

Wire message-reclassified sidecar events through the main process to
the renderer, where reclassified messages are filtered out of the main
transcript and collected into a collapsible ThinkingProcess component.

Main process changes:
- Route message-reclassified via dedicated onMessageReclassified callback
- Add applyMessageReclassified handler that sets messageKind and emits
  the session event for the renderer
- Forward assistant-intent and reasoning-delta as turn-scoped events

Renderer changes:
- Split session.messages into visibleMessages and thinkingMessages
- Render ThinkingProcess above the last assistant message
- ThinkingProcess auto-expands during active turns, collapses on finish
- Update messagePhase to skip thinking-kind messages for final detection

Tests:
- 3 new sessionWorkspace tests for reclassification apply/dedup/ignore
- 2 new messagePhase tests for thinking-kind handling
- Updated runTurnPending test fixtures for new callback

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/main/AryxAppService.ts

@@ -10,6 +10,7 @@ import type {
   ExitPlanModeRequestedEvent,
   MessageMode,
   McpOauthRequiredEvent,
+  MessageReclassifiedEvent,
   RunTurnCustomAgentConfig,
   RunTurnToolingConfig,
   SidecarCapabilities,
@@ -1364,6 +1365,9 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
         async (event) => {
           await this.handleExitPlanModeRequested(workspace, session.id, event);
         },
+        async (event) => {
+          await this.applyMessageReclassified(workspace, session.id, event);
+        },
         async (event) => {
           await this.handleTurnScopedEvent(workspace, session.id, event);
         },
@@ -1715,6 +1719,31 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
     }
   }
 
+  private async applyMessageReclassified(
+    workspace: WorkspaceState,
+    sessionId: string,
+    event: MessageReclassifiedEvent,
+  ): Promise<void> {
+    const session = this.requireSession(workspace, sessionId);
+    const message = session.messages.find((m) => m.id === event.messageId);
+    if (!message || message.messageKind === 'thinking') {
+      return;
+    }
+
+    message.messageKind = 'thinking';
+    const occurredAt = nowIso();
+    session.updatedAt = occurredAt;
+    await this.workspaceRepository.save(workspace);
+
+    this.emitSessionEvent({
+      sessionId,
+      kind: 'message-reclassified',
+      occurredAt,
+      messageId: event.messageId,
+      messageKind: 'thinking',
+    });
+  }
+
   private async applyAgentActivity(
     workspace: WorkspaceState,
     sessionId: string,

src/main/sidecar/runTurnPending.ts

@@ -3,6 +3,7 @@ import type {
   ApprovalRequestedEvent,
   ExitPlanModeRequestedEvent,
   McpOauthRequiredEvent,
+  MessageReclassifiedEvent,
   TurnDeltaEvent,
   UserInputRequestedEvent,
   SubagentEvent,
@@ -12,6 +13,8 @@ import type {
   SessionCompactionEvent,
   PendingMessagesModifiedEvent,
   AssistantUsageEvent,
+  AssistantIntentEvent,
+  ReasoningDeltaEvent,
 } from '@shared/contracts/sidecar';
 import type { ChatMessageRecord } from '@shared/domain/session';
 
@@ -22,7 +25,9 @@ export type TurnScopedEvent =
   | SessionUsageEvent
   | SessionCompactionEvent
   | PendingMessagesModifiedEvent
-  | AssistantUsageEvent;
+  | AssistantUsageEvent
+  | AssistantIntentEvent
+  | ReasoningDeltaEvent;
 
 export interface RunTurnPendingCommand {
   kind: 'run-turn';
@@ -34,6 +39,7 @@ export interface RunTurnPendingCommand {
   onUserInput: (event: UserInputRequestedEvent) => void | Promise<void>;
   onMcpOAuthRequired: (event: McpOauthRequiredEvent) => void | Promise<void>;
   onExitPlanMode: (event: ExitPlanModeRequestedEvent) => void | Promise<void>;
+  onMessageReclassified: (event: MessageReclassifiedEvent) => void | Promise<void>;
   onTurnScopedEvent: (event: TurnScopedEvent) => void | Promise<void>;
   errored: boolean;
 }

src/main/sidecar/sidecarProcess.ts

@@ -9,6 +9,7 @@ import type {
   SidecarCapabilities,
   SidecarEvent,
   TurnDeltaEvent,
+  MessageReclassifiedEvent,
   UserInputRequestedEvent,
   McpOauthRequiredEvent,
   ExitPlanModeRequestedEvent,
@@ -134,9 +135,10 @@ export class SidecarClient {
     onUserInput: (event: UserInputRequestedEvent) => void | Promise<void>,
     onMcpOAuthRequired: (event: McpOauthRequiredEvent) => void | Promise<void>,
     onExitPlanMode: (event: ExitPlanModeRequestedEvent) => void | Promise<void>,
+    onMessageReclassified: (event: MessageReclassifiedEvent) => void | Promise<void>,
     onTurnScopedEvent: (event: TurnScopedEvent) => void | Promise<void>,
   ): Promise<ChatMessageRecord[]> {
-    return this.dispatch<ChatMessageRecord[]>(command, onDelta, onActivity, onApproval, onUserInput, onMcpOAuthRequired, onExitPlanMode, onTurnScopedEvent);
+    return this.dispatch<ChatMessageRecord[]>(command, onDelta, onActivity, onApproval, onUserInput, onMcpOAuthRequired, onExitPlanMode, onMessageReclassified, onTurnScopedEvent);
   }
 
   async resolveUserInput(userInputId: string, answer: string, wasFreeform: boolean): Promise<void> {
@@ -286,6 +288,7 @@ export class SidecarClient {
     onUserInput?: (event: UserInputRequestedEvent) => void | Promise<void>,
     onMcpOAuthRequired?: (event: McpOauthRequiredEvent) => void | Promise<void>,
     onExitPlanMode?: (event: ExitPlanModeRequestedEvent) => void | Promise<void>,
+    onMessageReclassified?: (event: MessageReclassifiedEvent) => void | Promise<void>,
     onTurnScopedEvent?: (event: TurnScopedEvent) => void | Promise<void>,
   ): Promise<TResult> {
     const state = await this.ensureProcess();
@@ -303,6 +306,7 @@ export class SidecarClient {
           onUserInput: onUserInput ?? (() => undefined),
           onMcpOAuthRequired: onMcpOAuthRequired ?? (() => undefined),
           onExitPlanMode: onExitPlanMode ?? (() => undefined),
+          onMessageReclassified: onMessageReclassified ?? (() => undefined),
           onTurnScopedEvent: onTurnScopedEvent ?? (() => undefined),
           errored: false,
         });
@@ -439,6 +443,11 @@ export class SidecarClient {
           this.invokeRunTurnHandler(event.requestId, pending, () => pending.onExitPlanMode(event));
         }
         return;
+      case 'message-reclassified':
+        if (pending.kind === 'run-turn' && shouldHandleRunTurnEvent(pending)) {
+          this.invokeRunTurnHandler(event.requestId, pending, () => pending.onMessageReclassified(event));
+        }
+        return;
       case 'subagent-event':
       case 'skill-invoked':
       case 'hook-lifecycle':
@@ -446,6 +455,8 @@ export class SidecarClient {
       case 'session-compaction':
       case 'pending-messages-modified':
       case 'assistant-usage':
+      case 'assistant-intent':
+      case 'reasoning-delta':
         if (pending.kind === 'run-turn' && shouldHandleRunTurnEvent(pending)) {
           this.invokeRunTurnHandler(event.requestId, pending, () => pending.onTurnScopedEvent(event));
         }

src/renderer/components/ChatPane.tsx

@@ -12,6 +12,7 @@ import { UserInputBanner } from '@renderer/components/chat/UserInputBanner';
 import { InlineApprovalPill, InlineModelPill, InlineTerminalPill, InlineThinkingPill, InlineToolsPill } from '@renderer/components/chat/InlinePills';
 import { InlinePromptPill } from '@renderer/components/chat/InlinePromptPill';
 import { ThinkingDots } from '@renderer/components/chat/ThinkingDots';
+import { ThinkingProcess } from '@renderer/components/chat/ThinkingProcess';
 import { SubagentActivityList } from '@renderer/components/chat/SubagentActivityCard';
 import { getAssistantMessagePhase } from '@renderer/lib/messagePhase';
 import type { ApprovalDecision } from '@shared/domain/approval';
@@ -115,12 +116,28 @@ export function ChatPane({
   const composerRef = useRef<MarkdownComposerHandle>(null);
 
   const isSessionBusy = session.status === 'running';
+  const { visibleMessages, thinkingMessages } = useMemo(() => {
+    const visible: typeof session.messages = [];
+    const thinking: typeof session.messages = [];
+    for (const message of session.messages) {
+      if (message.messageKind === 'thinking') {
+        thinking.push(message);
+      } else {
+        visible.push(message);
+      }
+    }
+    return { visibleMessages: visible, thinkingMessages: thinking };
+  }, [session.messages]);
   const lastAssistantIndex = useMemo(() => {
-    for (let i = session.messages.length - 1; i >= 0; i--) {
+    for (let i = visibleMessages.length - 1; i >= 0; i--) {
-      if (session.messages[i].role === 'assistant') return i;
+      if (visibleMessages[i].role === 'assistant') return i;
     }
     return -1;
-  }, [session.messages]);
+  }, [visibleMessages]);
+  const turnStartedAt = useMemo(() => {
+    if (session.runs.length === 0) return undefined;
+    return session.runs[0].startedAt;
+  }, [session.runs]);
   const pendingApproval = session.pendingApproval?.status === 'pending' ? session.pendingApproval : undefined;
   const queuedApprovals = (session.pendingApprovalQueue ?? []).filter((a) => a.status === 'pending');
   const totalPendingCount = (pendingApproval ? 1 : 0) + queuedApprovals.length;
@@ -358,7 +375,7 @@ export function ChatPane({
               />
             )}
             <div className="space-y-1">
-              {session.messages.map((message, index) => {
+              {visibleMessages.map((message, index) => {
                 const isUser = message.role === 'user';
                 const isEditing = editingMessageId === message.id;
                 const isLastAssistant = index === lastAssistantIndex;
@@ -376,101 +393,122 @@ export function ChatPane({
                 const phaseLabel =
                   phase === 'thinking' ? 'Thinking' : phase === 'final' ? 'Final' : undefined;
                 const showActions = !isSessionBusy && !message.pending;
+                const showThinkingBefore = isLastAssistant && thinkingMessages.length > 0;
 
                 return (
-                  <div className="message-enter group py-3" data-message-id={message.id} key={message.id}>
+                  <div key={message.id}>
-                    <div className="flex gap-3">
+                    {showThinkingBefore && (
-                      <div
+                      <div className="py-2">
-                        className={`mt-0.5 flex size-7 shrink-0 items-center justify-center rounded-full ${
+                        <ThinkingProcess
-                          isUser ? 'brand-gradient-bg text-white' : 'bg-[var(--color-surface-2)] text-[var(--color-text-secondary)]'
+                          messages={thinkingMessages}
-                        }`}
+                          isActive={isSessionBusy}
-                      >
+                          turnStartedAt={turnStartedAt}
-                        {isUser ? <User className="size-3.5" /> : <Bot className="size-3.5" />}
+                        />
                       </div>
-                      <div className="min-w-0 flex-1">
+                    )}
-                        <div className="mb-1 flex items-center gap-2 text-[12px] font-medium text-[var(--color-text-secondary)]">
+                    <div className="message-enter group py-3" data-message-id={message.id}>
-                          <span>{message.authorName}</span>
+                      <div className="flex gap-3">
-                          {message.isPinned && (
+                        <div
-                            <Bookmark className="size-3 fill-[var(--color-accent-sky)] text-[var(--color-accent-sky)]" />
+                          className={`mt-0.5 flex size-7 shrink-0 items-center justify-center rounded-full ${
-                          )}
+                            isUser ? 'brand-gradient-bg text-white' : 'bg-[var(--color-surface-2)] text-[var(--color-text-secondary)]'
-                          {!isUser && phaseLabel && (
+                          }`}
-                            <span
+                        >
-                              className={`inline-flex items-center rounded-full border px-2 py-0.5 text-[10px] font-semibold uppercase tracking-[0.08em] ${assistantBadgeClass}`}
+                          {isUser ? <User className="size-3.5" /> : <Bot className="size-3.5" />}
-                            >
-                              {phaseLabel}
-                            </span>
-                          )}
-                          {showActions && (
-                            <div className="ml-auto">
-                              <MessageActions
-                                message={message}
-                                isLastAssistant={isLastAssistant}
-                                onCopy={() => handleCopyMessage(message.content)}
-                                onPin={() => onPinMessage?.(message.id, !message.isPinned)}
-                                onBranch={() => onBranchFromMessage?.(message.id)}
-                                onRegenerate={onRegenerateMessage ? () => onRegenerateMessage(message.id) : undefined}
-                                onEdit={onEditAndResendMessage && isUser ? () => setEditingMessageId(message.id) : undefined}
-                              />
-                            </div>
-                          )}
                         </div>
-
+                        <div className="min-w-0 flex-1">
-                        {/* Edit mode */}
+                          <div className="mb-1 flex items-center gap-2 text-[12px] font-medium text-[var(--color-text-secondary)]">
-                        {isEditing ? (
+                            <span>{message.authorName}</span>
-                          <MessageEditComposer
+                            {message.isPinned && (
-                            initialContent={message.content}
+                              <Bookmark className="size-3 fill-[var(--color-accent-sky)] text-[var(--color-accent-sky)]" />
-                            onSave={(content) => handleEditSave(message.id, content)}
-                            onCancel={() => setEditingMessageId(undefined)}
-                          />
-                        ) : (
-                          <div
-                            className={
-                              isUser
-                                ? 'text-[14px] leading-relaxed text-[var(--color-text-primary)]'
-                                : `rounded-xl border px-4 py-3 text-[14px] leading-relaxed text-[var(--color-text-primary)] ${assistantContainerClass}`
-                            }
-                          >
-                            {/* Attachment thumbnails */}
-                            {isUser && message.attachments && message.attachments.length > 0 && (
-                              <div className="mb-2 flex flex-wrap gap-2">
-                                {message.attachments.map((att, attIdx) =>
-                                  isImageAttachment(att) ? (
-                                    <img
-                                      key={attIdx}
-                                      alt={getAttachmentDisplayName(att)}
-                                      className="max-h-48 max-w-xs rounded-lg border border-[var(--color-border)] object-cover"
-                                      src={`data:${att.mimeType};base64,${att.data}`}
-                                    />
-                                  ) : (
-                                    <div
-                                      key={attIdx}
-                                      className="flex items-center gap-1.5 rounded-lg border border-[var(--color-border)] bg-[var(--color-surface-2)] px-2 py-1 text-[11px] text-[var(--color-text-secondary)]"
-                                    >
-                                      <Paperclip className="size-3" />
-                                      {getAttachmentDisplayName(att)}
-                                    </div>
-                                  ),
-                                )}
-                              </div>
                             )}
-                            {!isUser && message.pending ? (
+                            {!isUser && phaseLabel && (
-                              <div className="whitespace-pre-wrap break-words text-[14px] leading-relaxed text-[var(--color-text-primary)]">
+                              <span
-                                {message.content}
+                                className={`inline-flex items-center rounded-full border px-2 py-0.5 text-[10px] font-semibold uppercase tracking-[0.08em] ${assistantBadgeClass}`}
-                              </div>
+                              >
-                            ) : (
+                                {phaseLabel}
-                              <MarkdownContent content={message.content} />
+                              </span>
                             )}
-                            {message.pending && message.content && (
+                            {showActions && (
-                              <span className="mt-1 inline-block h-4 w-[2px] animate-pulse rounded-sm bg-[var(--color-accent)]" />
+                              <div className="ml-auto">
+                                <MessageActions
+                                  message={message}
+                                  isLastAssistant={isLastAssistant}
+                                  onCopy={() => handleCopyMessage(message.content)}
+                                  onPin={() => onPinMessage?.(message.id, !message.isPinned)}
+                                  onBranch={() => onBranchFromMessage?.(message.id)}
+                                  onRegenerate={onRegenerateMessage ? () => onRegenerateMessage(message.id) : undefined}
+                                  onEdit={onEditAndResendMessage && isUser ? () => setEditingMessageId(message.id) : undefined}
+                                />
+                              </div>
                             )}
                           </div>
-                        )}
+
-                        {message.pending && !message.content && <ThinkingDots />}
+                          {/* Edit mode */}
+                          {isEditing ? (
+                            <MessageEditComposer
+                              initialContent={message.content}
+                              onSave={(content) => handleEditSave(message.id, content)}
+                              onCancel={() => setEditingMessageId(undefined)}
+                            />
+                          ) : (
+                            <div
+                              className={
+                                isUser
+                                  ? 'text-[14px] leading-relaxed text-[var(--color-text-primary)]'
+                                  : `rounded-xl border px-4 py-3 text-[14px] leading-relaxed text-[var(--color-text-primary)] ${assistantContainerClass}`
+                              }
+                            >
+                              {/* Attachment thumbnails */}
+                              {isUser && message.attachments && message.attachments.length > 0 && (
+                                <div className="mb-2 flex flex-wrap gap-2">
+                                  {message.attachments.map((att, attIdx) =>
+                                    isImageAttachment(att) ? (
+                                      <img
+                                        key={attIdx}
+                                        alt={getAttachmentDisplayName(att)}
+                                        className="max-h-48 max-w-xs rounded-lg border border-[var(--color-border)] object-cover"
+                                        src={`data:${att.mimeType};base64,${att.data}`}
+                                      />
+                                    ) : (
+                                      <div
+                                        key={attIdx}
+                                        className="flex items-center gap-1.5 rounded-lg border border-[var(--color-border)] bg-[var(--color-surface-2)] px-2 py-1 text-[11px] text-[var(--color-text-secondary)]"
+                                      >
+                                        <Paperclip className="size-3" />
+                                        {getAttachmentDisplayName(att)}
+                                      </div>
+                                    ),
+                                  )}
+                                </div>
+                              )}
+                              {!isUser && message.pending ? (
+                                <div className="whitespace-pre-wrap break-words text-[14px] leading-relaxed text-[var(--color-text-primary)]">
+                                  {message.content}
+                                </div>
+                              ) : (
+                                <MarkdownContent content={message.content} />
+                              )}
+                              {message.pending && message.content && (
+                                <span className="mt-1 inline-block h-4 w-[2px] animate-pulse rounded-sm bg-[var(--color-accent)]" />
+                              )}
+                            </div>
+                          )}
+                          {message.pending && !message.content && <ThinkingDots />}
+                        </div>
                       </div>
                     </div>
                   </div>
                 );
               })}
+              {thinkingMessages.length > 0 && lastAssistantIndex < 0 && (
+                <div className="py-2">
+                  <ThinkingProcess
+                    messages={thinkingMessages}
+                    isActive={isSessionBusy}
+                    turnStartedAt={turnStartedAt}
+                  />
+                </div>
+              )}
             </div>
             {activeSubagents && activeSubagents.length > 0 && (
               <div className="px-6 py-1">

src/renderer/components/chat/ThinkingProcess.tsx

@@ -0,0 +1,120 @@
+import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
+import { Brain, ChevronDown, ChevronRight } from 'lucide-react';
+
+import type { ChatMessageRecord } from '@shared/domain/session';
+
+interface ThinkingProcessProps {
+  messages: ChatMessageRecord[];
+  isActive: boolean;
+  turnStartedAt?: string;
+}
+
+export function ThinkingProcess({ messages, isActive, turnStartedAt }: ThinkingProcessProps) {
+  const [expanded, setExpanded] = useState(false);
+  const wasActiveRef = useRef(isActive);
+
+  // Auto-expand when the turn is active and thinking messages appear.
+  // Auto-collapse once the turn finishes.
+  useEffect(() => {
+    if (isActive && messages.length > 0) {
+      setExpanded(true);
+    } else if (wasActiveRef.current && !isActive) {
+      setExpanded(false);
+    }
+    wasActiveRef.current = isActive;
+  }, [isActive, messages.length]);
+
+  const toggle = useCallback(() => setExpanded((prev) => !prev), []);
+
+  const elapsed = useMemo(() => {
+    if (!turnStartedAt || messages.length === 0) return undefined;
+    const start = new Date(turnStartedAt).getTime();
+    const lastMessage = messages[messages.length - 1];
+    const end = isActive ? Date.now() : new Date(lastMessage.createdAt).getTime();
+    const seconds = Math.max(0, Math.round((end - start) / 1000));
+    if (seconds < 2) return undefined;
+    return seconds >= 60 ? `${Math.floor(seconds / 60)}m ${seconds % 60}s` : `${seconds}s`;
+  }, [turnStartedAt, messages, isActive]);
+
+  if (messages.length === 0) {
+    return null;
+  }
+
+  const stepCount = messages.length;
+  const summaryParts: string[] = [];
+  if (elapsed) summaryParts.push(`${elapsed}`);
+  summaryParts.push(`${stepCount} ${stepCount === 1 ? 'step' : 'steps'}`);
+
+  return (
+    <div className="thinking-process-enter mb-2 overflow-hidden rounded-lg border border-[var(--color-border)]/50 bg-[var(--color-surface-1)]/60">
+      <button
+        type="button"
+        onClick={toggle}
+        onKeyDown={(e) => { if (e.key === ' ') { e.preventDefault(); toggle(); } }}
+        aria-expanded={expanded}
+        className="flex w-full items-center gap-2 px-3 py-2 text-left text-[12px] text-[var(--color-text-muted)] transition-colors hover:bg-[var(--color-surface-2)]/50"
+      >
+        <Brain className="size-3.5 shrink-0 text-[var(--color-accent-purple)]" />
+        {isActive ? (
+          <span className="flex items-center gap-1.5">
+            <span className="text-[var(--color-text-secondary)]">Thinking</span>
+            <ThinkingPulse />
+          </span>
+        ) : (
+          <span className="text-[var(--color-text-secondary)]">
+            Thought for {summaryParts.join(' · ')}
+          </span>
+        )}
+        <span className="ml-auto shrink-0">
+          {expanded
+            ? <ChevronDown className="size-3 text-[var(--color-text-muted)]" />
+            : <ChevronRight className="size-3 text-[var(--color-text-muted)]" />}
+        </span>
+      </button>
+      {expanded && (
+        <div className="border-t border-[var(--color-border)]/30 px-3 py-2">
+          <div className="space-y-1.5">
+            {messages.map((message) => (
+              <ThinkingStep key={message.id} message={message} />
+            ))}
+          </div>
+        </div>
+      )}
+    </div>
+  );
+}
+
+function ThinkingStep({ message }: { message: ChatMessageRecord }) {
+  const preview = useMemo(() => truncatePreview(message.content, 180), [message.content]);
+
+  return (
+    <div className="flex gap-2 text-[12px] leading-relaxed">
+      <span className="mt-0.5 shrink-0 text-[var(--color-text-muted)]">▸</span>
+      <div className="min-w-0">
+        {message.authorName && (
+          <span className="mr-1.5 font-medium text-[var(--color-text-secondary)]">
+            {message.authorName}
+          </span>
+        )}
+        <span className="text-[var(--color-text-muted)]">{preview}</span>
+      </div>
+    </div>
+  );
+}
+
+function ThinkingPulse() {
+  return (
+    <span className="inline-flex items-center gap-0.5">
+      <span className="thinking-dot size-1 rounded-full bg-[var(--color-accent-purple)]" />
+      <span className="thinking-dot size-1 rounded-full bg-[var(--color-accent-purple)]" />
+      <span className="thinking-dot size-1 rounded-full bg-[var(--color-accent-purple)]" />
+    </span>
+  );
+}
+
+function truncatePreview(text: string, maxLength: number): string {
+  const firstLine = text.split('\n')[0] ?? '';
+  const cleaned = firstLine.trim();
+  if (cleaned.length <= maxLength) return cleaned;
+  return `${cleaned.slice(0, maxLength)}…`;
+}

src/renderer/lib/messagePhase.ts

@@ -11,6 +11,10 @@ export function getAssistantMessagePhase(
     return 'default';
   }
 
+  if (message.messageKind === 'thinking') {
+    return 'default';
+  }
+
   if (message.pending) {
     return 'thinking';
   }
@@ -26,7 +30,7 @@ export function getAssistantMessagePhase(
 function findLastCompletedAssistantIndex(messages: ChatMessageRecord[]): number {
   for (let index = messages.length - 1; index >= 0; index -= 1) {
     const message = messages[index];
-    if (message.role === 'assistant' && !message.pending) {
+    if (message.role === 'assistant' && !message.pending && message.messageKind !== 'thinking') {
       return index;
     }
   }

src/renderer/lib/sessionWorkspace.ts

@@ -41,6 +41,8 @@ function applySessionEvent(session: SessionRecord, event: SessionEventRecord): S
       return applyMessageDeltaEvent(session, event);
     case 'message-complete':
       return applyMessageCompleteEvent(session, event);
+    case 'message-reclassified':
+      return applyMessageReclassifiedEvent(session, event);
     case 'run-updated':
       return applyRunUpdatedEvent(session, event);
     default:
@@ -172,6 +174,30 @@ function applyMessageCompleteEvent(session: SessionRecord, event: SessionEventRe
   };
 }
 
+function applyMessageReclassifiedEvent(session: SessionRecord, event: SessionEventRecord): SessionRecord {
+  if (!event.messageId || !event.messageKind) {
+    return session;
+  }
+
+  const messageIndex = session.messages.findIndex((message) => message.id === event.messageId);
+  if (messageIndex < 0) {
+    return session;
+  }
+
+  const existing = session.messages[messageIndex];
+  if (existing.messageKind === event.messageKind) {
+    return session;
+  }
+
+  const nextMessages = session.messages.slice();
+  nextMessages[messageIndex] = { ...existing, messageKind: event.messageKind };
+  return {
+    ...session,
+    messages: nextMessages,
+    updatedAt: event.occurredAt,
+  };
+}
+
 function applyRunUpdatedEvent(session: SessionRecord, event: SessionEventRecord): SessionRecord {
   if (!event.run) {
     return session;

src/renderer/styles.css

@@ -626,6 +626,19 @@ body {
   animation: banner-slide-in 0.25s cubic-bezier(0.16, 1, 0.3, 1);
 }
 
+/* ── Thinking process section ────────────────────────────────── */
+
+@keyframes thinking-process-in {
+  from {
+    opacity: 0;
+    transform: translateY(-4px);
+  }
+}
+
+.thinking-process-enter {
+  animation: thinking-process-in 0.2s cubic-bezier(0.16, 1, 0.3, 1) both;
+}
+
 /* ── Respect reduced motion ──────────────────────────────────── */
 
 @media (prefers-reduced-motion: reduce) {
@@ -637,7 +650,8 @@ body {
   .message-enter,
   .msg-actions-enter,
   .session-item-enter,
-  .banner-slide-enter {
+  .banner-slide-enter,
+  .thinking-process-enter {
     animation: none;
   }
 }

tests/main/runTurnPending.test.ts

@@ -19,6 +19,7 @@ describe('run turn pending helpers', () => {
       onUserInput: () => undefined,
       onExitPlanMode: () => undefined,
       onMcpOAuthRequired: () => undefined,
+      onMessageReclassified: () => undefined,
       onTurnScopedEvent: () => undefined,
       errored: false,
     };
@@ -45,6 +46,7 @@ describe('run turn pending helpers', () => {
       onUserInput: () => undefined,
       onExitPlanMode: () => undefined,
       onMcpOAuthRequired: () => undefined,
+      onMessageReclassified: () => undefined,
       onTurnScopedEvent: () => undefined,
       errored: false,
     };

tests/renderer/messagePhase.test.ts

@@ -85,4 +85,59 @@ describe('assistant message phase', () => {
 
     expect(getAssistantMessagePhase(session, session.messages[0], 0)).toBe('default');
   });
+
+  test('returns default for thinking-kind messages regardless of other state', () => {
+    const session = createSession([
+      {
+        id: 'msg-1',
+        role: 'assistant',
+        authorName: 'Primary Agent',
+        content: 'Let me search...',
+        createdAt: '2026-03-23T00:00:00.000Z',
+        messageKind: 'thinking',
+      },
+      {
+        id: 'msg-2',
+        role: 'assistant',
+        authorName: 'Primary Agent',
+        content: 'Here is the result.',
+        createdAt: '2026-03-23T00:00:01.000Z',
+      },
+    ]);
+
+    expect(getAssistantMessagePhase(session, session.messages[0], 0)).toBe('default');
+    expect(getAssistantMessagePhase(session, session.messages[1], 1)).toBe('final');
+  });
+
+  test('skips thinking messages when determining the last completed assistant', () => {
+    const session = createSession([
+      {
+        id: 'msg-1',
+        role: 'assistant',
+        authorName: 'Primary Agent',
+        content: 'Let me search...',
+        createdAt: '2026-03-23T00:00:00.000Z',
+        messageKind: 'thinking',
+      },
+      {
+        id: 'msg-2',
+        role: 'assistant',
+        authorName: 'Primary Agent',
+        content: 'More searching...',
+        createdAt: '2026-03-23T00:00:01.000Z',
+        messageKind: 'thinking',
+      },
+      {
+        id: 'msg-3',
+        role: 'assistant',
+        authorName: 'Primary Agent',
+        content: 'Final answer.',
+        createdAt: '2026-03-23T00:00:02.000Z',
+      },
+    ]);
+
+    expect(getAssistantMessagePhase(session, session.messages[0], 0)).toBe('default');
+    expect(getAssistantMessagePhase(session, session.messages[1], 1)).toBe('default');
+    expect(getAssistantMessagePhase(session, session.messages[2], 2)).toBe('final');
+  });
 });

tests/renderer/sessionWorkspace.test.ts

@@ -281,4 +281,73 @@ describe('session workspace helpers', () => {
       } satisfies SessionEventRecord),
     ).toBe(workspace);
   });
+
+  test('reclassifies a message as thinking when message-reclassified event arrives', () => {
+    const workspace = applySessionEventWorkspace(createWorkspace(), {
+      sessionId: 'session-1',
+      kind: 'message-delta',
+      occurredAt: '2026-03-23T00:00:01.000Z',
+      messageId: 'assistant-1',
+      authorName: 'Primary Agent',
+      contentDelta: 'Let me search...',
+      content: 'Let me search...',
+    } satisfies SessionEventRecord);
+
+    const reclassified = applySessionEventWorkspace(workspace, {
+      sessionId: 'session-1',
+      kind: 'message-reclassified',
+      occurredAt: '2026-03-23T00:00:02.000Z',
+      messageId: 'assistant-1',
+      messageKind: 'thinking',
+    } satisfies SessionEventRecord);
+
+    expect(reclassified?.sessions[0].messages[0]).toMatchObject({
+      id: 'assistant-1',
+      messageKind: 'thinking',
+    });
+  });
+
+  test('ignores message-reclassified for an already reclassified message', () => {
+    let workspace = applySessionEventWorkspace(createWorkspace(), {
+      sessionId: 'session-1',
+      kind: 'message-delta',
+      occurredAt: '2026-03-23T00:00:01.000Z',
+      messageId: 'assistant-1',
+      authorName: 'Primary Agent',
+      contentDelta: 'Let me search...',
+      content: 'Let me search...',
+    } satisfies SessionEventRecord);
+
+    workspace = applySessionEventWorkspace(workspace, {
+      sessionId: 'session-1',
+      kind: 'message-reclassified',
+      occurredAt: '2026-03-23T00:00:02.000Z',
+      messageId: 'assistant-1',
+      messageKind: 'thinking',
+    } satisfies SessionEventRecord);
+
+    const duplicate = applySessionEventWorkspace(workspace, {
+      sessionId: 'session-1',
+      kind: 'message-reclassified',
+      occurredAt: '2026-03-23T00:00:03.000Z',
+      messageId: 'assistant-1',
+      messageKind: 'thinking',
+    } satisfies SessionEventRecord);
+
+    // Should return the same reference (no change)
+    expect(duplicate).toBe(workspace);
+  });
+
+  test('ignores message-reclassified for unknown message ids', () => {
+    const workspace = createWorkspace();
+    const result = applySessionEventWorkspace(workspace, {
+      sessionId: 'session-1',
+      kind: 'message-reclassified',
+      occurredAt: '2026-03-23T00:00:01.000Z',
+      messageId: 'nonexistent',
+      messageKind: 'thinking',
+    } satisfies SessionEventRecord);
+
+    expect(result).toBe(workspace);
+  });
 });