From 36689751c3c8a9872f84cc916a6322b24942319e Mon Sep 17 00:00:00 2001
From: Mason Huang <masonxhuang@tencent.com>
Date: Wed, 29 Apr 2026 17:15:43 +0800
Subject: [PATCH] fix: cover plain streaming json parse failures

---
 ...i-embedded-helpers.formatassistanterrortext.test.ts |  8 ++++++++
 src/agents/pi-embedded-helpers/errors.test.ts          | 10 ++++++++++
 .../pi-embedded-helpers/sanitize-user-facing-text.ts   |  2 +-
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/src/agents/pi-embedded-helpers.formatassistanterrortext.test.ts b/src/agents/pi-embedded-helpers.formatassistanterrortext.test.ts
index 34a520f5b6e..78b6091c96a 100644
--- a/src/agents/pi-embedded-helpers.formatassistanterrortext.test.ts
+++ b/src/agents/pi-embedded-helpers.formatassistanterrortext.test.ts
@@ -483,6 +483,14 @@ describe("sanitizeUserFacingText — streaming JSON parse error (#59076)", () =>
     expect(result).toBe("LLM streaming response contained a malformed fragment. Please try again.");
   });
 
+  it.each([
+    "Unexpected end of JSON input",
+    "Unexpected non-whitespace character after JSON at position 4",
+  ])("rewrites plain JSON.parse error variants in error context: %s", (text) => {
+    const result = sanitizeUserFacingText(text, { errorContext: true });
+    expect(result).toBe("LLM streaming response contained a malformed fragment. Please try again.");
+  });
+
   it("does not rewrite JSON parse error when not in error context", () => {
     // When not in error context, the text could be legitimate assistant content
     // mentioning JSON errors. Don't rewrite.
diff --git a/src/agents/pi-embedded-helpers/errors.test.ts b/src/agents/pi-embedded-helpers/errors.test.ts
index 53cee0368c2..e8cd0d9ffd8 100644
--- a/src/agents/pi-embedded-helpers/errors.test.ts
+++ b/src/agents/pi-embedded-helpers/errors.test.ts
@@ -19,6 +19,16 @@ describe("formatAssistantErrorText streaming JSON parse classification", () => {
     );
   });
 
+  it.each([
+    "Unexpected end of JSON input",
+    "Unexpected non-whitespace character after JSON at position 4",
+  ])("suppresses plain JSON.parse streaming fragment failures: %s", (errorMessage) => {
+    const msg = makeAssistantError(errorMessage);
+    expect(formatAssistantErrorText(msg)).toBe(
+      "LLM streaming response contained a malformed fragment. Please try again.",
+    );
+  });
+
   it("suppresses structured Anthropic tool-call delta parse failures", () => {
     const msg = makeAssistantError(
       'Could not parse Anthropic SSE event content_block_delta: Unexpected end of JSON input; data={"type":"content_block_delta","delta":{"type":"input_json_delta","partial_json":"{\\"path\\":"},"index":0}',
diff --git a/src/agents/pi-embedded-helpers/sanitize-user-facing-text.ts b/src/agents/pi-embedded-helpers/sanitize-user-facing-text.ts
index 378e0e6639c..1091b5c2984 100644
--- a/src/agents/pi-embedded-helpers/sanitize-user-facing-text.ts
+++ b/src/agents/pi-embedded-helpers/sanitize-user-facing-text.ts
@@ -223,7 +223,7 @@ export function isStreamingJsonParseError(raw: string): boolean {
     return true;
   }
 
-  return /^(?:Expected (?:',' or '\}' after property value|double-quoted property name|':' after property name|',' or '\]' after array element)|Unterminated string) in JSON at position \d+(?: \(line \d+ column \d+\))?$/i.test(
+  return /^(?:Unexpected end of JSON input|Unexpected non-whitespace character after JSON at position \d+(?: \(line \d+ column \d+\))?|(?:Expected (?:',' or '\}' after property value|double-quoted property name|':' after property name|',' or '\]' after array element)|Unterminated string) in JSON at position \d+(?: \(line \d+ column \d+\))?)$/i.test(
     trimmed,
   );
 }