fix: name max_buffer_size in the buffer-overflow error message

src/claude_agent_sdk/_errors.py

@@ -120,10 +120,16 @@ def __init__(
 class CLIJSONDecodeError(ClaudeSDKError):
     """Raised when unable to decode JSON from CLI output."""
 
-    def __init__(self, line: str, original_error: Exception):
+    def __init__(self, line: str, original_error: Exception, hint: str | None = None):
         self.line = line
         self.original_error = original_error
-        super().__init__(f"Failed to decode JSON: {line[:100]}...")
+        self.hint = hint
+        message = f"Failed to decode JSON: {line[:100]}..."
+        # Appended AFTER the truncated line so actionable guidance survives:
+        # `line` is cut at 100 chars, so anything folded into it can be lost.
+        if hint:
+            message = f"{message} {hint}"
+        super().__init__(message)
 
 
 class MessageParseError(ClaudeSDKError):

src/claude_agent_sdk/_internal/transport/subprocess_cli.py

@@ -1095,6 +1095,11 @@ def guard(length: int) -> None:
                     ValueError(
                         f"Buffer size {length} exceeds limit {self._max_buffer_size}"
                     ),
+                    hint=(
+                        "Large tool results (file reads, images, MCP responses) "
+                        "can exceed the default; raise it with "
+                        "ClaudeAgentOptions(max_buffer_size=...)."
+                    ),
                 )
 
         try:

tests/test_errors.py

@@ -110,3 +110,13 @@ def test_json_decode_error(self):
             assert error.line == "{invalid json}"
             assert error.original_error == e
             assert "Failed to decode JSON" in str(error)
+            assert error.hint is None
+
+    def test_json_decode_error_hint_survives_line_truncation(self):
+        """The hint must outlive the 100-char truncation of `line`."""
+        error = CLIJSONDecodeError("x" * 500, ValueError("boom"), hint="Do the thing.")
+        assert error.hint == "Do the thing."
+        assert str(error).endswith("Do the thing.")
+        # The line is still truncated; the hint is what stays readable.
+        assert "x" * 100 in str(error)
+        assert "x" * 101 not in str(error)

tests/test_subprocess_buffering.py

@@ -281,6 +281,9 @@ async def _test() -> None:
                     pass
 
             assert f"maximum buffer size of {custom_limit} bytes" in str(exc_info.value)
+            # The error must name the option that fixes it, so users reach for
+            # max_buffer_size instead of editing the installed package.
+            assert "max_buffer_size" in str(exc_info.value)
 
         anyio.run(_test)