[Bug] Tool-use block markup intermittently corrupted with stray token prefix

Bug Description
Title: Tool-call markup intermittently corrupted ("court" prefix) → "malformed and could not be parsed"

Summary:
Tool invocations (function_calls / tool_use blocks) are intermittently emitted
with corrupted markup. The block starts with a stray token (e.g. "court")
instead of the proper function_calls opening tag, so the harness rejects it
with "Your tool call was malformed and could not be parsed."

Symptom:

• The same tool call, retried verbatim, usually succeeds on the next attempt.
• Affected tools observed: Edit, Write, Bash, Read (all recovered on retry).
• No data loss — the failure happens before the tool runs.

Conditions that seem to trigger it:

• Long sessions with large accumulated context (multiple big tasks).
• Emitting a tool call immediately after a long natural-language response.
• Packing multiple tool calls into a single message.

Environment:

• Claude Code (CLI)
• Model: Opus 4.8 (1M context), max effort
• Long-running session

Reproducibility:

• Intermittent / non-deterministic. No reliable repro steps.
• Retrying the identical call typically resolves it.
• This session's transcript is itself a live example (please inspect the

attached conversation context).

Workarounds currently used:

• Retry the failed call.
• Minimize preamble text before a tool call; issue one tool at a time.
• /compact appears to reduce frequency by shrinking context.

Environment Info

• Platform: darwin
• Terminal: vscode
• Version: 2.1.158
• Feedback ID: 6b0ec702-6a20-42a7-af9a-191f3954eb42

Errors

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