Harness spec 3.1.0-draft: the prefix stays still

Measured on 2026-11-05 against a local model's prompt cache: a harness
that rebuilds its system prompt for every request re-reads the whole
session whenever any part changes (a date at midnight: 16,912 tokens,
99 % -> 0 % cached, 139 s). context.md §10: the system prompt is made
once per session and resent; no clock in it; mid-session changes go as
a <session-note> on the next user message (loop.json context.note); the
tool list is fixed for the session, a requires that comes and goes
answers unavailable instead (plan_submit gains requires: plan); §7: the
compaction summary is the next turn of the same conversation, not a
separate request with a pasted transcript; cached tokens are recorded.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

harness/VERSION

@@ -1 +1 @@
-3.0.0
+3.1.0-draft