[Bug] Frequent "tool call could not be parsed" errors with parallel/non-ASCII tool calls

Bug Description

Bug Description

Frequent "The model's tool call could not be parsed (retry also failed)." errors
during a normal session. It happens repeatedly — often multiple times within a
single user turn — across different tool types (Bash, AskUserQuestion, parallel
Bash calls). The retry shown in the UI also fails, so the turn is interrupted and
I have to re-prompt the model to continue.

Frequency / Impact

• High frequency: occurred ~6+ times in a single short session.
• Not tied to one specific tool — seen on plain Bash, on AskUserQuestion, and on

parallel (multiple-tool-use-in-one-message) Bash calls.

• User-visible: each occurrence dumps a "Your tool call was malformed and could

not be parsed. Please retry." line into the transcript and stalls progress.

Repro (best guess — not yet deterministic)

1. Run a normal coding/ops session in Claude Code (Opus 4.8).
2. Issue requests that lead the model to emit tool calls, including parallel

tool calls and AskUserQuestion.

1. Intermittently, the tool call fails to parse and the retry also fails.

I could not pin down a 100% reproduction; it appears intermittent rather than
input-specific. Capturing the raw model output that failed to parse (and logging
it to the feedback payload automatically) would help diagnose whether it's a
truncation, an encoding issue, or a schema-serialization problem.

Notes

• Model: Claude Opus 4.8 (claude-opus-4-8)
• Possibly correlated with parallel tool calls and/or non-ASCII (Japanese) content

in tool arguments, but unconfirmed.

• The "Errors" array in the feedback form was empty even though the failures were

clearly visible in the UI — the malformed tool call does not seem to be captured
in the structured error log.

---
（日本語補足）
通常セッション中に "tool call could not be parsed" が頻発（1セッションで6回以上）。
Bash 単体・AskUserQuestion・並列 Bash 呼び出しのいずれでも発生し、UI 上の自動リトライも
失敗してターンが中断する。再現は input 依存ではなく断続的。日本語（非ASCII）引数や並列
ツール呼び出しとの相関が疑われるが未確定。パースに失敗した生の model output を feedback に
自動添付してもらえると原因切り分け（truncation / encoding / schema 化の失敗）が進む。

Environment Info

• Platform: darwin
• Terminal: ghostty
• Version: 2.1.156
• Feedback ID: 4aa76c7e-3db0-4fc1-8e44-543cdc931eb5

Errors

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