diff --git a/apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts b/apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts
index e7c113405eb7..f58861da57b2 100644
--- a/apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts
+++ b/apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts
@@ -5362,8 +5362,55 @@ export function makeClaudeAdapterV2(
             context.toolCalls.delete(toolCall.nativeItemId);
           }
 
-          const assistantText = assistantTextFromSdkMessage(message);
           const assistantParentToolUseId = parentToolUseIdFromSdkMessage(message);
+          if (message.type === "assistant" && assistantParentToolUseId !== null) {
+            // Claude never streams subagent output, so each thinking block
+            // arrives whole in its own snapshot and lands in the child thread.
+            const thinking = message.message.content.flatMap((block) =>
+              block.type === "thinking" && block.thinking.trim().length > 0 ? [block.thinking] : [],
+            );
+            const subagent =
+              thinking.length === 0
+                ? undefined
+                : yield* resolveSubagentByToolUseId(context, assistantParentToolUseId);
+            if (subagent !== undefined) {
+              const now = yield* DateTime.now;
+              for (const [index, text] of thinking.entries()) {
+                const nativeItemId = `${message.uuid}:thinking:${index}`;
+                yield* emitProviderEvent({
+                  type: "turn_item.updated",
+                  driver: CLAUDE_PROVIDER,
+                  turnItem: {
+                    id: idAllocator.derive.turnItemFromProviderItem({
+                      driver: CLAUDE_PROVIDER,
+                      nativeItemId,
+                    }),
+                    threadId: subagent.childThreadId,
+                    runId: null,
+                    nodeId: subagent.childRootNodeId,
+                    providerThreadId: null,
+                    providerTurnId: null,
+                    nativeItemRef: {
+                      driver: CLAUDE_PROVIDER,
+                      nativeId: nativeItemId,
+                      strength: "strong",
+                    },
+                    parentItemId: null,
+                    ordinal: ++subagent.nextChildItemOrdinal,
+                    type: "reasoning",
+                    title: "Thinking",
+                    text,
+                    streaming: false,
+                    status: "completed",
+                    startedAt: now,
+                    completedAt: now,
+                    updatedAt: now,
+                  },
+                });
+              }
+            }
+          }
+          const assistantText = assistantTextFromSdkMessage(message);
           if (
             assistantText !== null &&
             assistantText.text.length > 0 &&
diff --git a/apps/server/src/orchestration-v2/testkit/fixtures/claude_background_subagent_lifecycle/output.ts b/apps/server/src/orchestration-v2/testkit/fixtures/claude_background_subagent_lifecycle/output.ts
index c3b9d297cc4d..7be360e0f701 100644
--- a/apps/server/src/orchestration-v2/testkit/fixtures/claude_background_subagent_lifecycle/output.ts
+++ b/apps/server/src/orchestration-v2/testkit/fixtures/claude_background_subagent_lifecycle/output.ts
@@ -145,6 +145,41 @@ export function assertClaudeBackgroundSubagentLifecycleOutput(
   assert.isDefined(agentAChild);
   assert.deepEqual(assistantTexts(agentAChild), ["A_FIRST", "A_SECOND"]);
 
+  // The recording's subagent thinking lands in each child thread, before the
+  // reply it led to, and never in the parent.
+  const thinkingOf = (child: OrchestrationV2ThreadProjection | undefined) =>
+    (child?.turnItems ?? []).flatMap((item) =>
+      item.type === "reasoning" && item.title === "Thinking" ? [item] : [],
+    );
+  const agentAThinking = thinkingOf(agentAChild);
+  assert.lengthOf(agentAThinking, 2, "both of Agent A's runs thought before replying");
+  assert.include(agentAThinking[0]?.text, '"A_FIRST"');
+  assert.include(agentAThinking[1]?.text, '"A_SECOND"');
+  for (const item of agentAThinking) {
+    assert.equal(item.status, "completed");
+    assert.isFalse(item.streaming);
+    assert.isNull(item.runId);
+  }
+  const agentAOrder = agentAChild.turnItems.flatMap((item) =>
+    item.type === "assistant_message"
+      ? [item.text.trim()]
+      : item.type === "reasoning" && item.title === "Thinking"
+        ? ["thinking"]
+        : [],
+  );
+  assert.deepEqual(agentAOrder, ["thinking", "A_FIRST", "thinking", "A_SECOND"]);
+  const agentBChild =
+    agentB?.childThreadId == null ? undefined : result.projections.get(agentB.childThreadId);
+  assert.lengthOf(thinkingOf(agentBChild), 1);
+  assert.include(thinkingOf(agentBChild)[0]?.text, "B_DONE");
+  const subagentThinking = new Set(
+    [...agentAThinking, ...thinkingOf(agentBChild)].map((item) => item.text),
+  );
+  assert.isFalse(
+    thinkingOf(projection).some((item) => subagentThinking.has(item.text)),
+    "subagent thinking leaked into the parent thread",
+  );
+
   // Subagents appear in background_tasks_changed but never on the roster.
   assert.isFalse(
     result.domainEvents.some(