When tool_preview_length is 0 (default for platforms without a tier
default, like Session), verbose mode was truncating args JSON to 200
characters. Since the user explicitly opted into verbose mode, they
expect full tool call detail — the 200-char cap defeated the purpose.
Now: tool_preview_length=0 means no truncation in verbose mode.
Positive values still cap as before. Platform message-length limits
handle overflow naturally.
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