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));
         }