diff --git a/packages/web/src/__tests__/stepsToMessages.test.ts b/packages/web/src/__tests__/stepsToMessages.test.ts
index 92dd75f..404018d 100644
--- a/packages/web/src/__tests__/stepsToMessages.test.ts
+++ b/packages/web/src/__tests__/stepsToMessages.test.ts
@@ -428,4 +428,32 @@ describe("stepsToMessages", () => {
     expect(msgs[3].role).toBe("assistant");
     expect(msgs).toHaveLength(4);
   });
+
+  // ── Subagent steps ──
+
+  it("converts invoke_subagent tool call to subagent system message", () => {
+    const step: TrajectoryStep = {
+      type: "CORTEX_STEP_TYPE_TOOL_CALL",
+      metadata: {
+        toolCall: {
+          name: "invoke_subagent",
+          argumentsJson: JSON.stringify({
+            Subagents: [
+              {
+                Role: "Config Auditor",
+                TypeName: "research",
+                Prompt: "Audit all config files",
+              },
+            ],
+            toolAction: "Invoking research subagent",
+          }),
+        },
+      },
+    };
+
+    const msgs = stepsToMessages([step]);
+    expect(msgs).toHaveLength(1);
+    expect(msgs[0].type).toBe("CORTEX_STEP_TYPE_SUBAGENT");
+    expect(msgs[0].step).toBe(step);
+  });
 });
diff --git a/packages/web/src/components/ChatPanel.tsx b/packages/web/src/components/ChatPanel.tsx
index eb0842b..4a3f792 100644
--- a/packages/web/src/components/ChatPanel.tsx
+++ b/packages/web/src/components/ChatPanel.tsx
@@ -24,6 +24,7 @@ import {
   CommandCard,
   CodeActionCard,
   FilePermissionCard,
+  SubagentCard,
 } from "./StepCards";
 import { getAskQuestionRequest, getFilePermissionRequest } from "../utils/stepCards";
 import {
@@ -313,6 +314,13 @@ function SystemMessage({
         </div>
       );
     }
+    if (msg.type === "CORTEX_STEP_TYPE_SUBAGENT") {
+      return (
+        <div className="message system">
+          <SubagentCard step={msg.step} />
+        </div>
+      );
+    }
   }
 
   return (
diff --git a/packages/web/src/components/Icons.tsx b/packages/web/src/components/Icons.tsx
index ae0b5d7..8e55698 100644
--- a/packages/web/src/components/Icons.tsx
+++ b/packages/web/src/components/Icons.tsx
@@ -247,3 +247,11 @@ export const IconGear = ({ size = 16, className }: IconProps) =>
 
 export const IconChevronLeft = ({ size = 16, className }: IconProps) =>
   d(size, className, "m15 18-6-6 6-6");
+
+export const IconUsers = ({ size = 16, className }: IconProps) =>
+  m(size, className, [
+    "M16 21v-2a4 4 0 0 0-4-4H6a4 4 0 0 0-4 4v2",
+    "M9 11a4 4 0 1 0 0-8 4 4 0 0 0 0 8z",
+    "M22 21v-2a4 4 0 0 0-3-3.87",
+    "M16 3.13a4 4 0 0 1 0 7.75",
+  ]);
diff --git a/packages/web/src/components/StepCards.tsx b/packages/web/src/components/StepCards.tsx
index ff1ccb0..0387cd9 100644
--- a/packages/web/src/components/StepCards.tsx
+++ b/packages/web/src/components/StepCards.tsx
@@ -8,6 +8,7 @@ import {
   IconFileText,
   IconLock,
   IconMessageCircle,
+  IconUsers,
 } from "./Icons";
 import type {
   AskQuestionEntry,
@@ -592,3 +593,66 @@ export function CodeActionCard({ step }: CodeActionCardProps) {
     </div>
   );
 }
+
+// ── Subagent Card ──
+
+export function SubagentCard({ step }: { step: TrajectoryStep }) {
+  const [expanded, setExpanded] = useState(false);
+  const toolCall = step.metadata?.toolCall;
+  const toolName = toolCall?.name ?? "invoke_subagent";
+
+  let subagents: Array<{ Role?: string; TypeName?: string; Prompt?: string; Model?: string }> = [];
+  let toolAction = (step as any).toolAction ?? "";
+  let toolSummary = (step as any).toolSummary ?? "";
+
+  if (toolCall?.argumentsJson) {
+    try {
+      const parsed = JSON.parse(toolCall.argumentsJson);
+      if (Array.isArray(parsed.Subagents)) {
+        subagents = parsed.Subagents;
+      }
+      if (parsed.toolAction) toolAction = parsed.toolAction;
+      if (parsed.toolSummary) toolSummary = parsed.toolSummary;
+    } catch {
+      // ignore
+    }
+  }
+
+  const primaryRole =
+    subagents[0]?.Role ||
+    toolSummary ||
+    (toolName === "define_subagent" ? "Subagent Defined" : "Subagent Invoked");
+  const primaryTypeName = subagents[0]?.TypeName || "subagent";
+  const promptText = subagents[0]?.Prompt || "";
+  const isRunning =
+    step.status === "CORTEX_STEP_STATUS_RUNNING" ||
+    step.status === "CORTEX_STEP_STATUS_WAITING";
+
+  return (
+    <div className={`chat-block step-card subagent-card ${isRunning ? "cmd-wait" : ""}`}>
+      <button
+        className="step-card-header"
+        onClick={() => promptText && setExpanded((v) => !v)}
+        title={promptText ? "Toggle subagent prompt" : undefined}
+      >
+        <span className="step-card-icon">
+          <IconUsers size={12} />
+        </span>
+        <span className="subagent-role">{primaryRole}</span>
+        <span className="subagent-type-badge">{primaryTypeName}</span>
+        {toolAction && <span className="step-card-desc">{toolAction}</span>}
+        {promptText && (
+          <span className={`step-card-chevron ${expanded ? "open" : ""}`}>
+            ▾
+          </span>
+        )}
+      </button>
+      {expanded && promptText && (
+        <div className="step-card-subagent-prompt">
+          <div className="subagent-prompt-label">Instructions:</div>
+          <pre className="subagent-prompt-text">{promptText}</pre>
+        </div>
+      )}
+    </div>
+  );
+}
diff --git a/packages/web/src/styles/step-cards.css b/packages/web/src/styles/step-cards.css
index 3430973..5b6a5a9 100644
--- a/packages/web/src/styles/step-cards.css
+++ b/packages/web/src/styles/step-cards.css
@@ -688,3 +688,51 @@
   border-color: var(--accent-hover);
   box-shadow: 0 2px 12px rgba(99, 102, 241, 0.3);
 }
+
+/* ── Subagent Card ── */
+
+.subagent-card .subagent-role {
+  font-weight: 600;
+  color: var(--text-primary);
+  margin-right: 6px;
+}
+
+.subagent-type-badge {
+  font-size: 10px;
+  font-weight: 600;
+  text-transform: uppercase;
+  letter-spacing: 0.04em;
+  padding: 2px 6px;
+  border-radius: 4px;
+  background: var(--bg-hover);
+  color: var(--accent);
+  border: 1px solid var(--border-subtle);
+  margin-right: 8px;
+}
+
+.step-card-subagent-prompt {
+  border-top: 1px solid var(--border-subtle);
+  padding: 10px 12px;
+  font-size: 12px;
+  background: var(--bg-surface);
+  border-bottom-left-radius: var(--radius-md);
+  border-bottom-right-radius: var(--radius-md);
+}
+
+.subagent-prompt-label {
+  font-weight: 600;
+  color: var(--text-muted);
+  margin-bottom: 4px;
+  font-size: 11px;
+  text-transform: uppercase;
+  letter-spacing: 0.03em;
+}
+
+.subagent-prompt-text {
+  white-space: pre-wrap;
+  word-break: break-word;
+  font-family: var(--font-mono);
+  color: var(--text-secondary);
+  margin: 0;
+  line-height: 1.4;
+}
diff --git a/packages/web/src/transforms/stepsToMessages.ts b/packages/web/src/transforms/stepsToMessages.ts
index b25482d..7242953 100644
--- a/packages/web/src/transforms/stepsToMessages.ts
+++ b/packages/web/src/transforms/stepsToMessages.ts
@@ -46,6 +46,26 @@ export function stepsToMessages(steps: TrajectoryStep[]): ChatMessage[] {
       continue;
     }
 
+    const toolName = step.metadata?.toolCall?.name ?? "";
+    const isSubagent =
+      toolName === "invoke_subagent" ||
+      toolName === "define_subagent" ||
+      toolName === "manage_subagents" ||
+      toolName === "send_message" ||
+      type === "CORTEX_STEP_TYPE_INVOKE_SUBAGENT" ||
+      type === "CORTEX_STEP_TYPE_SUBAGENT";
+
+    if (isSubagent) {
+      messages.push({
+        role: "system",
+        content: "",
+        stepIndex: i,
+        type: "CORTEX_STEP_TYPE_SUBAGENT",
+        step,
+      });
+      continue;
+    }
+
     if (type === "CORTEX_STEP_TYPE_USER_INPUT" && step.userInput?.items) {
       const text = textFromItems(step.userInput.items);
       const media = step.userInput.media;