diff --git a/src/wrapper/normalize.mjs b/src/wrapper/normalize.mjs
index deae2c4..7e9e7d1 100644
--- a/src/wrapper/normalize.mjs
+++ b/src/wrapper/normalize.mjs
@@ -1,3 +1,30 @@
+const STOP_REASON_MAP = new Map([
+  ["stop", "stop"],
+  ["end_turn", "stop"],
+  ["endturn", "stop"],
+  ["length", "length"],
+  ["tooluse", "toolUse"],
+  ["tool_use", "toolUse"],
+  ["aborted", "aborted"],
+  ["error", "error"],
+]);
+
+export function normalizeStopReason(value) {
+  if (typeof value !== "string") {
+    return { stopReason: undefined, rawStopReason: undefined };
+  }
+
+  const rawStopReason = value.trim();
+  if (!rawStopReason) {
+    return { stopReason: undefined, rawStopReason: undefined };
+  }
+
+  return {
+    stopReason: STOP_REASON_MAP.get(rawStopReason.toLowerCase()),
+    rawStopReason,
+  };
+}
+
 export function normalizePiEvent(event) {
   if (event?.type === "tool_execution_start") {
     return {
@@ -14,11 +41,14 @@ export function normalizePiEvent(event) {
       .join("\n")
       .trim();
 
+    const { stopReason, rawStopReason } = normalizeStopReason(event.message.stopReason);
+
     return {
       type: "assistant_text",
       text,
       model: event.message.model,
-      stopReason: event.message.stopReason,
+      stopReason,
+      rawStopReason,
       usage: event.message.usage,
     };
   }
diff --git a/src/wrapper/normalize.test.ts b/src/wrapper/normalize.test.ts
index 78feff4..1f0df24 100644
--- a/src/wrapper/normalize.test.ts
+++ b/src/wrapper/normalize.test.ts
@@ -1,6 +1,6 @@
 import test from "node:test";
 import assert from "node:assert/strict";
-import { normalizePiEvent } from "./normalize.mjs";
+import { normalizePiEvent, normalizeStopReason } from "./normalize.mjs";
 
 test("normalizePiEvent converts tool start events into protocol tool-call records", () => {
   const normalized = normalizePiEvent({
@@ -16,7 +16,26 @@ test("normalizePiEvent converts tool start events into protocol tool-call record
   });
 });
 
-test("normalizePiEvent converts assistant message_end into a final-text record", () => {
+test("normalizeStopReason maps raw tool-use variants to canonical toolUse", () => {
+  assert.deepEqual(normalizeStopReason("toolUse"), {
+    stopReason: "toolUse",
+    rawStopReason: "toolUse",
+  });
+
+  assert.deepEqual(normalizeStopReason("tool_use"), {
+    stopReason: "toolUse",
+    rawStopReason: "tool_use",
+  });
+});
+
+test("normalizeStopReason preserves unknown stop reasons without marking them terminal", () => {
+  assert.deepEqual(normalizeStopReason("custom_reason"), {
+    stopReason: undefined,
+    rawStopReason: "custom_reason",
+  });
+});
+
+test("normalizePiEvent converts assistant message_end into canonical final-text record", () => {
   const normalized = normalizePiEvent({
     type: "message_end",
     message: {
@@ -32,7 +51,8 @@ test("normalizePiEvent converts assistant message_end into a final-text record",
     type: "assistant_text",
     text: "Final answer",
     model: "anthropic/claude-sonnet-4-5",
-    stopReason: "end_turn",
+    stopReason: "stop",
+    rawStopReason: "end_turn",
     usage: { input: 10, output: 5, totalTokens: 15, cost: { total: 0.001 } },
   });
 });