The 40-character truncation of tool call IDs in helper.go caused collisions
when models (like deepseek-v4-flash) generated longer IDs, leading to
"Duplicate value for 'tool_call_id'" errors. Removed the limit to allow
full unique IDs.
DeepSeek: updated reasoning_content injection to use an empty string
instead of a space, better matching provider expectations for history.
Improved API error reporting across all providers by capturing raw body
content when response parsing fails or returns empty strings.
