diff --git a/packages/server/src/server/agent/providers/claude/agent.background-subagent.test.ts b/packages/server/src/server/agent/providers/claude/agent.background-subagent.test.ts
index 630bdbf0a6..7c0beed569 100644
--- a/packages/server/src/server/agent/providers/claude/agent.background-subagent.test.ts
+++ b/packages/server/src/server/agent/providers/claude/agent.background-subagent.test.ts
@@ -431,6 +431,7 @@ describe("background Claude subagents", () => {
         type: "sub_agent",
         subAgentType: "general-purpose",
         description: "Count files here",
+        log: "[Bash] ls -1",
       },
     });
   });
diff --git a/packages/server/src/server/agent/providers/claude/agent.ts b/packages/server/src/server/agent/providers/claude/agent.ts
index aa60e40462..3cd1b9aa63 100644
--- a/packages/server/src/server/agent/providers/claude/agent.ts
+++ b/packages/server/src/server/agent/providers/claude/agent.ts
@@ -2094,18 +2094,29 @@ class ClaudeAgentSession implements AgentSession {
     getToolInput: (toolUseId) => this.toolUseCache.get(toolUseId)?.input ?? null,
     readWorkflowResult: readClaudeWorkflowResultFile,
   });
+  /**
+   * Subagent tool calls Claude has already answered, with the input they were launched with. A
+   * background child is answered at launch and streams its frames afterwards.
+   */
+  private readonly settledSubagentToolCalls = new Map<
+    string,
+    { item: Extract<AgentTimelineItem, { type: "tool_call" }>; input: AgentMetadata | null }
+  >();
   private readonly sidechainTracker = new ClaudeSidechainTracker({
-    getToolInput: (toolUseId) => this.toolUseCache.get(toolUseId)?.input ?? null,
+    getToolInput: (toolUseId) =>
+      this.toolUseCache.get(toolUseId)?.input ??
+      this.settledSubagentToolCalls.get(toolUseId)?.input ??
+      null,
     // Releases that predate the task protocol announce nothing, so the tracker keeps deriving
     // identity and status from frames for them. Detecting the capability beats comparing version
     // strings: it reacts to what this session actually does.
     isDescriptorOwnedElsewhere: () => this.taskProtocolSource.isActive,
-    // The parent's tool call owns its card once its result arrives. A background child streams
-    // its frames after Claude has already answered the call, and re-emitting the card from them
-    // would replace the settled card with an unlabeled, running one.
+    // A background child streams its frames after Claude has already answered the call, so its
+    // card is rebuilt from the settled call: a running one would replace the settled, labeled card.
     needsSyntheticParentToolCard: (toolUseId) =>
-      this.toolUseCache.has(toolUseId) &&
+      (this.toolUseCache.has(toolUseId) || this.settledSubagentToolCalls.has(toolUseId)) &&
       this.taskProtocolSource.needsSyntheticParentToolCard(toolUseId),
+    getSettledParentToolCall: (toolUseId) => this.settledSubagentToolCalls.get(toolUseId)?.item,
   });
   private persistedHistory: PersistedTimelineEntry[] = [];
   private persistedProviderSubagentEvents: Extract<
@@ -2711,6 +2722,7 @@ class ClaudeAgentSession implements AgentSession {
     this.cancelCurrentTurn = null;
     this.turnState = "idle";
     this.sidechainTracker.clear();
+    this.settledSubagentToolCalls.clear();
     this.taskProtocolSource.reset();
     this.input?.end();
     this.query?.close?.();
@@ -5308,28 +5320,22 @@ class ClaudeAgentSession implements AgentSession {
     const { images, text } = splitClaudeToolResultImages(block.content);
     const output = this.buildToolOutput(text, block, entry);
 
-    if (block.is_error) {
-      this.pushToolCall(
-        mapClaudeFailedToolCall({
+    const settledToolCall = block.is_error
+      ? mapClaudeFailedToolCall({
           name: toolName,
           callId,
           input: entry?.input ?? null,
           output: output ?? null,
           error: { ...block, content: text },
-        }),
-        items,
-      );
-    } else {
-      this.pushToolCall(
-        mapClaudeCompletedToolCall({
+        })
+      : mapClaudeCompletedToolCall({
           name: toolName,
           callId,
           input: entry?.input ?? null,
           output: output ?? null,
-        }),
-        items,
-      );
-    }
+        });
+    this.pushToolCall(settledToolCall, items);
+    this.rememberSettledSubagentToolCall(settledToolCall, entry);
 
     for (const image of images) {
       const imageItem = renderProviderImageOutputAsAssistantMarkdown(image, {
@@ -5345,6 +5351,14 @@ class ClaudeAgentSession implements AgentSession {
     }
   }
 
+  private rememberSettledSubagentToolCall(
+    item: Extract<AgentTimelineItem, { type: "tool_call" }> | null,
+    entry: ToolUseCacheEntry | undefined,
+  ): void {
+    if (!item || !this.taskProtocolSource.resolveSubagentId(item.callId)) return;
+    this.settledSubagentToolCalls.set(item.callId, { item, input: entry?.input ?? null });
+  }
+
   private buildToolOutput(
     content: unknown,
     block: ClaudeContentChunk,
diff --git a/packages/server/src/server/agent/providers/claude/sidechain-tracker.ts b/packages/server/src/server/agent/providers/claude/sidechain-tracker.ts
index 6973d1db5d..da6faafa90 100644
--- a/packages/server/src/server/agent/providers/claude/sidechain-tracker.ts
+++ b/packages/server/src/server/agent/providers/claude/sidechain-tracker.ts
@@ -14,6 +14,8 @@ interface ClaudeContentChunk {
   [key: string]: unknown;
 }
 
+type ClaudeToolCallItem = Extract<AgentTimelineItem, { type: "tool_call" }>;
+
 interface SubAgentActionEntry {
   index: number;
   toolName: string;
@@ -60,6 +62,7 @@ export class ClaudeSidechainTracker {
   private readonly getToolInput: (toolUseId: string) => AgentMetadata | null | undefined;
   private readonly isDescriptorOwnedElsewhere: () => boolean;
   private readonly needsSyntheticParentToolCard: (toolUseId: string) => boolean;
+  private readonly getSettledParentToolCall: (toolUseId: string) => ClaudeToolCallItem | undefined;
 
   constructor(input: {
     getToolInput: (toolUseId: string) => AgentMetadata | null | undefined;
@@ -70,10 +73,17 @@ export class ClaudeSidechainTracker {
      */
     isDescriptorOwnedElsewhere?: () => boolean;
     needsSyntheticParentToolCard?: (toolUseId: string) => boolean;
+    /**
+     * The parent's tool call once Claude has answered it. A background child streams its frames
+     * after that answer, so its card keeps the settled status and output and gains the child's
+     * action log.
+     */
+    getSettledParentToolCall?: (toolUseId: string) => ClaudeToolCallItem | undefined;
   }) {
     this.getToolInput = input.getToolInput;
     this.isDescriptorOwnedElsewhere = input.isDescriptorOwnedElsewhere ?? (() => false);
     this.needsSyntheticParentToolCard = input.needsSyntheticParentToolCard ?? (() => true);
+    this.getSettledParentToolCall = input.getSettledParentToolCall ?? (() => undefined);
   }
 
   handleMessage(message: SDKMessage, parentToolUseId: string): AgentStreamEvent[] {
@@ -115,17 +125,19 @@ export class ClaudeSidechainTracker {
       return [];
     }
 
-    const toolCall = mapClaudeRunningToolCall({
-      name: "Task",
-      callId: parentToolUseId,
-      input: null,
-      output: null,
-    });
+    const toolCall =
+      this.getSettledParentToolCall(parentToolUseId) ??
+      mapClaudeRunningToolCall({
+        name: "Task",
+        callId: parentToolUseId,
+        input: null,
+        output: null,
+      });
     if (!toolCall) {
       return [];
     }
 
-    const detail: Extract<AgentTimelineItem, { type: "tool_call" }>["detail"] = {
+    const detail: ClaudeToolCallItem["detail"] = {
       type: "sub_agent",
       ...(state.subAgentType ? { subAgentType: state.subAgentType } : {}),
       ...(state.description ? { description: state.description } : {}),