Splits the array-form defaultConvertToLlm into a single-message convertMessageToLlm that embedders can delegate every core role to instead of duplicating the conversion. Adds the optional images field on CompactionSummaryMessage so the converter attaches snapcompact frames after the summary text (snapcompact strategy lands next). Renames every convertToLlm call site in compaction.ts and branch-summarization.ts to the canonical defaultConvertToLlm.\n\nNote: the bundled CHANGELOG entries also cover the supersede-reads, snapcompact, and steering-queue fixes that follow in this batch (the entries land in directly adjacent lines and cannot be split by diff).
can1357
bc5af8d9be