From 8481d977bb952f6fa99dcbebc1026c5603c2794d Mon Sep 17 00:00:00 2001
From: Spencer <spencertang@google.com>
Date: Wed, 15 Apr 2026 15:48:15 +0000
Subject: [PATCH] fix: add back global string limit gracefully returning a
 valid json string

---
 packages/core/src/telemetry/trace.test.ts | 17 +++++++++++++++++
 packages/core/src/telemetry/trace.ts      |  8 ++++++++
 2 files changed, 25 insertions(+)

diff --git a/packages/core/src/telemetry/trace.test.ts b/packages/core/src/telemetry/trace.test.ts
index e9d2dc47dd..41bba1a3df 100644
--- a/packages/core/src/telemetry/trace.test.ts
+++ b/packages/core/src/telemetry/trace.test.ts
@@ -124,6 +124,23 @@ describe('truncateForTelemetry', () => {
     );
   });
 
+  it('should enforce a global payload string limit without breaking JSON', () => {
+    const obj = {
+      a: 'x'.repeat(100),
+      b: 'y'.repeat(100),
+    };
+    // Capping global string length to 50
+    const result = truncateForTelemetry(obj, 100, 100, 4, 50) as string;
+
+    // It should replace the entire object with a valid JSON string indicating truncation
+    expect(result).toBe(
+      '"[TRUNCATED: Payload exceeded global limit of 50 characters. Original length: 215]"',
+    );
+
+    // Prove it remains perfectly parseable JSON
+    expect(() => JSON.parse(result)).not.toThrow();
+  });
+
   it('should stringify objects unchanged if within maxLength', () => {
     const obj = { a: 1 };
     expect(truncateForTelemetry(obj, 100)).toBe(JSON.stringify(obj));
diff --git a/packages/core/src/telemetry/trace.ts b/packages/core/src/telemetry/trace.ts
index bd9b32c119..fc323961ac 100644
--- a/packages/core/src/telemetry/trace.ts
+++ b/packages/core/src/telemetry/trace.ts
@@ -67,6 +67,7 @@ export function truncateForTelemetry(
   maxStringLength = 10000,
   maxArrayLength = 100,
   maxDepth = 4,
+  maxGlobalStringLength = 50000,
 ): AttributeValue | undefined {
   const truncateObj = (v: unknown, depth: number): unknown => {
     if (typeof v === 'string') {
@@ -149,6 +150,13 @@ export function truncateForTelemetry(
 
   const stringified = safeJsonStringify(truncated);
 
+  if (stringified.length > maxGlobalStringLength) {
+    const graphemes = Array.from(stringified);
+    if (graphemes.length > maxGlobalStringLength) {
+      return `"[TRUNCATED: Payload exceeded global limit of ${maxGlobalStringLength} characters. Original length: ${graphemes.length}]"`;
+    }
+  }
+
   return stringified as AttributeValue;
 }