fix: repair unescaped quotes in tool-call arguments

Author: elkaix

.changeset/tool-args-escape-repair.md

@@ -2,4 +2,4 @@
 "@pythoughts/pythinker-code": patch
 ---
 
-Repair invalid escape sequences in model-written tool arguments instead of failing the tool call.
+Repair invalid escape sequences and unescaped quotes in model-written tool arguments instead of failing the tool call.

packages/agent-core/src/loop/tool-call.ts

@@ -313,10 +313,11 @@ export function parseToolCallArguments(
 }
 
 /**
- * Models sometimes emit markdown-style escapes (\* \_ \[) inside JSON string
- * values; strict JSON.parse rejects them while streaming previews tolerate
- * them, so the call dies only at preflight. Rewrite ONLY invalid escapes to a
- * literal backslash + character, leaving valid escapes and structure alone.
+ * Models sometimes emit invalid escapes (\* \_ \[) or unescaped quotes inside
+ * JSON string values. Rewrite invalid escapes to a literal backslash +
+ * character and quotes that cannot terminate the string to escaped quotes.
+ * A content quote followed by a structural character is ambiguous and still
+ * closes the string; if reparsing fails, the original parse error is reported.
  * Returns null when nothing was repaired.
  */
 function repairInvalidStringEscapes(raw: string): string | null {
@@ -327,8 +328,22 @@ function repairInvalidStringEscapes(raw: string): string | null {
   for (let index = 0; index < raw.length; index += 1) {
     const character = raw[index];
     if (character === '"') {
-      inString = !inString;
-      result += character;
+      if (!inString) {
+        inString = true;
+        result += character;
+        continue;
+      }
+
+      let lookahead = index + 1;
+      while (lookahead < raw.length && ' \t\n\r'.includes(raw[lookahead]!)) lookahead += 1;
+      const next = raw[lookahead];
+      if (next === undefined || ',:}]'.includes(next)) {
+        inString = false;
+        result += character;
+      } else {
+        result += '\\"';
+        repaired = true;
+      }
       continue;
     }
     if (!inString || character !== '\\') {

packages/agent-core/test/loop/tool-call.e2e.test.ts

@@ -138,6 +138,47 @@ describe('parseToolCallArguments', () => {
     expect(result).toEqual({ success: true, data: { a: '\\u12ZZ' } });
   });
 
+  it('repairs unescaped quotes inside items-array string values', () => {
+    const result = parseToolCallArguments(
+      '{"items":[{"prompt":"Review the "config" module carefully","i":"review config"}]}',
+    );
+
+    expect(result).toEqual({
+      success: true,
+      data: { items: [{ prompt: 'Review the "config" module carefully', i: 'review config' }] },
+    });
+  });
+
+  it('leaves a quote before a structural character unchanged', () => {
+    const raw = '{"a":"done","b":1}';
+
+    expect(parseToolCallArguments(raw)).toEqual({ success: true, data: JSON.parse(raw) });
+  });
+
+  it('repairs invalid escapes and unescaped quotes together', () => {
+    const result = parseToolCallArguments('{"a":"bold \\*x and a "quoted" word"}');
+
+    expect(result).toEqual({ success: true, data: { a: 'bold \\*x and a "quoted" word' } });
+  });
+
+  it('recognizes a string terminator separated from structure by whitespace', () => {
+    const result = parseToolCallArguments('{"a":"text" , "b":"x "y" z"}');
+
+    expect(result).toEqual({ success: true, data: { a: 'text', b: 'x "y" z' } });
+  });
+
+  it('returns the original parse error after quote repair still fails', () => {
+    const raw = '{"a":[1,}';
+    let originalError = '';
+    try {
+      JSON.parse(raw);
+    } catch (error) {
+      originalError = error instanceof Error ? error.message : String(error);
+    }
+
+    expect(parseToolCallArguments(raw)).toEqual({ success: false, error: originalError });
+  });
+
   it('returns the original parse error for structurally broken input', () => {
     const raw = '{"a":"truncated';
     let originalError = '';