Session Handoff

Adapted from a proposal staged by an observe-work review (observation #6, 2026-09-08). The contract below is the proposal's; the verifier, the parse rule, the whitelist and the tests are task.110's.

Why this exists

A .agents/handoff.md opening with "Read this first if you are picking up work here" failed at exactly that job three times, and every failure was structural rather than authorial: