tony92921/dsh-compact-manager

Take over context compaction on both the manual and the automatic path, each runnable by a compaction model (falling back to a second model, or used directly) or by a mechanical fold that builds the summary card locally with no model call; the fold goes through the same official compaction transaction, so the replaced events stay in the append-only session log under their sequence numbers. It adapts code from dsh-compact-saviour and takes the mechanical fold from dsh-ledger-compact (both MIT) — install it instead of dsh-compact-saviour, not alongside it.