claude-code - 💡(How to fix) Fix [Bug] Tool-call parser rejects indented XML tags with vague "malformed" error

Bug Description

Title: Tool-call parser rejects leading whitespace on <invoke>/<parameter> tags with a vague "malformed" error

Description:

When a tool call is emitted with the <function_calls> / <invoke> / <parameter> tags indented (i.e. with leading whitespace) instead of starting at column 0, the call fails to parse and returns:

Your tool call was malformed and could not be parsed. Please retry.

The same call parses correctly when the tags start at the beginning of the line. The error message does not indicate the cause (leading whitespace), so it is easy to repeat the same mistake several times in a row before identifying it.

Steps to reproduce:

1. Emit a tool call where the <invoke> and <parameter> tags are indented, e.g.: <invoke name="Bash"> <parameter name="command">echo hi</parameter> </invoke>
2. Observe the "malformed and could not be parsed" error.
3. Re-emit the identical call with the tags at column 0 — it now parses and runs.

Requests:

• (a) Make the parser tolerant of leading whitespace — trim/ignore indentation before the tool-call tags so indented blocks parse correctly.
• (b) If strict parsing is intended, make the "malformed" error specific about the cause (e.g. "tool-call tags must start at the beginning of the line; leading whitespace found"), so the model can self-correct immediately instead of retrying blindly.

Impact: Causes repeated failed tool calls and wasted turns. Note: failed calls are rejected at parse time and are not executed, so there is no risk of partial/corrupted execution — but it interrupts progress.

Environment Info

• Platform: linux
• Terminal: wsl-Ubuntu-24.04-D
• Version: 2.1.158
• Feedback ID: 344f8a69-ea19-4057-a384-269425f487b9

Errors

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