D94 — Git-history changes digest

Status: implemented (2026-07-24).

Decision. changes_since is a read-only, server-side digest over Git history. The caller supplies an RFC3339 timestamp or <N>d/<N>h duration; no per-client last-seen state is stored. File changes aggregate by concept with newest-status-wins, including renames under their destination ID. .cartographer/ is ignored, while logs, maps and provisioning artifacts remain only in the other_changes count.

Rationale. Every MCP write already creates a Git commit, so Git supplies the authoritative timestamp, author and concept-level history without introducing client state. A compact per-concept aggregate answers a return-to-work digest without exposing raw commit noise.