Save partial checkpoint within a step (for long-running batch operations)
Source:R/04_checkpoint.R
save_partial_checkpoint.RdPartials are consumed on resume: the coding step reads
progressive_coding_partial.rds (via the pipeline) and the
sentiment step reads sentiment_done_partial.rds (inside
analyze_sentiment), so a crash mid-step does not re-pay the
LLM cost of completed entries. A successful save_checkpoint
for the step deletes its partial.